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Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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7

Physics Laboratory

PANEL MEMBERS

Samuel Werner, University of Missouri, Chair

Peter R. Almond, University of Louisville

C. Denise Caldwell, University of Central Florida

William C. Eckelman, National Institutes of Health

Leopoldo M. Falicov, University of California, Berkeley

Charlotte Froese Fischer, Vanderbilt University

George W. Flynn, Columbia University

Andrew U. Hazi, Lawrence Livermore National Laboratory

Klaus B. Jaeger, Lockheed Missiles & Space Company, Inc.

Anthony M. Johnson, AT&T Bell Laboratories

Andrew Kaldor, Exxon Research and Engineering Company

James E. Lawler, University of Wisconsin

Sam V. Nablo, Energy Sciences, Inc.

David A. Shirley, Pennsylvania State University

Robert Vessot, Harvard-Smithsonian Astrophysical Observatory

Philip Wychorski, Eastman Kodak Company

Submitted for the panel by its Chair, Samuel Werner, this assessment of the fiscal year 1993 activities of the Physics Laboratory is based on site visits to the laboratory by individual panel members in March and April 1993, on a meeting of the full panel in Gaithersburg, Maryland, on May 3-4, 1993, on the annual report of the laboratory, and on many research papers and reports provided to individual panel members.

LABORATORY OVERVIEW
Functions and Mission

The Physics Laboratory conducts long-term research in measurement science; develops new physical standards, measurement methods, and reference data; and promulgates these standards, methods, and data by providing measurement services, conducting workshops, publishing research results, and collaborating with industry, universities, and other agencies of government. Specifically, the Physics Laboratory establishes spectroscopic methods and standards for infrared, visible, ultraviolet, x-ray, gamma-ray, and neutron radiation; investigates the structure and dynamics of atoms and molecules, singly and in aggregate; and develops and disseminates national standards of time and frequency and for the measurement of optical and ionizing radiation by means of calibrations, measurement quality assurance, and standard reference materials. The laboratory generates, evaluates, and compiles atomic, molecular, optical,

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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and ionizing radiation data in response to national needs, develops and operates major radiation sources as user facilities, and maintains appropriate collaborations with other technical programs in NIST, the nation, and institutions throughout the world. The laboratory supports the research community and industry in communications, defense, energy, the environment, space, health, and transportation, as well as in specific technical areas such as lighting, microelectronics, and radiation.

The reorganization of NIST in fiscal years 1990 and 1991 resulted in the creation of the Physics Laboratory, which is organized into eight divisions--electron and optical physics, atomic physics, molecular physics, radiometric physics, quantum metrology, ionizing radiation, time and frequency, and quantum physics (Figure 7.1). (The Quantum Physics Division, which consists mainly of researchers at the Joint Institute for Laboratory Astrophysics at Boulder, Colorado, is assessed biennially and is not included in this assessment.) The organizational structure and priorities of the laboratory have been carefully adjusted over the past 2 years to meet the needs of the changing mission of NIST. A gradually increasing emphasis on applied physics, technology, and service to industry is evident. In her presentation to the panel, the laboratory's director defined the laboratory's mission as follows: “The mission of the Physics Laboratory is to support U.S. industry, government, and the scientific community through strongly coupled, complementary programs of services and research in the physical sciences.” The panel concluded that the operating structure of the Physics Laboratory is sufficiently functional and adaptable to fulfill this mission in the current rapidly changing national environment. The program planning is well conceived and has been increasingly effective in capturing resources for new initiatives.

Resources

During fiscal year 1993, the Physics Laboratory had 218 full-time permanent staff, 8 part-time staff, 15 postdoctoral associates, 146 guest researchers, and 21 term and intermittent appointees. Its operating budget was $42.4 million, of which 63 percent, or $26.7 million, was direct congressional appropriations to NIST.

Activities

The Physics Laboratory Annual Report 1992, presented to the panel at its meeting, shows that the laboratory has been able to sustain and even enhance its level of productivity in high-quality fundamental and applied research while providing important advice and service to the many governmental,

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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FIGURE 7.1 Organization and structure of the Physics Laboratory.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

university, and industrial “customers” of NIST's services and facilities. During fiscal year 1993, the Physics Laboratory received NIST's Stratton Award for an unusually significant contribution to scientific research, its Astin Award for outstanding achievement in the advancement of measurement science, and its Slichter Award for important contributions in building ties with industry. Three members of the staff were elected to fellowship in the American Physical Society, and one was elected to the National Academy of Sciences. One division chief received the Meritorious Executive Award from the Office of Personnel Management, and the Federal Laboratory Consortium Award was given to another staff scientist for transferring to industry an important optical-mechanical gravimeter. In addition, scientists in the Physics Laboratory won three Silver Medals and three Bronze Medals of the Department of Commerce. This long list of awards attests to the laboratory's high level of scientific and technological productivity and to its success in fulfilling its mission as judged by people and committees outside the laboratory.

The Physics Laboratory collaborates directly with approximately 100 U.S. firms. Eleven of these collaborations were established through the Advanced Technology Program (ATP), and about 25 are Cooperative Research and Development Agreements (CRADAs). Many of these interactions with industry involve scientists who also are carrying out fundamental research. Collaborations with industry span a wide range of companies and address many subjects, such as characterization of alternative refrigerants by high-resolution molecular spectroscopy, study of magnetic materials, advances in temperature controllers and solid-state lasers, and research in nuclear reactor dosimetry, mercury-free fluorescent lighting, and x-ray mammography.

During fiscal year 1993, the NIST director's office awarded the Physics Laboratory more than half of the funds available for the director's Competence Building Program ($800,000 per year). These funds went to programs in atom optics, diode lasers, and laser polarization of neutrons. These awards represent 5-year investments in areas of basic research likely to yield results and techniques important to future advanced technologies. The importance of diode lasers to atomic clocks, spectroscopy of pollutants, and communications is discussed below. The Laser Polarization of Neutrons Program will make the Advanced Neutron Source (a $2.5 billion Department of Energy program scheduled to come on-line in the early part of the next century at Oak Ridge National Laboratory) much more useful in the study of magnetic materials, biological materials, and polymers. Work in atom optics may yield a new type of Sagnac gyroscope. (The Sagnac effect is the shift in interference fringes from two coherent light beams traveling in opposite directions around a ring when the ring is rotated about an axis perpendicular to the ring.) The panel concludes that these long-term investments are well placed and utilize extremely talented people.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

In fiscal year 1992 and the first part of fiscal year 1993, the Physics Laboratory submitted 10 proposals for core support from NIST. Three of the proposals were included in the President's fiscal year 1994 budget for NIST: (1) “Atomic Scale Structure and Standards,” which will address the challenges of metrology for nanotechnology; (21) “Magnetic Measurement Technology,” which will address the improved measurement and standards needs of the information storage industry as it uses ever more sophisticated recording materials and devices; and (3) “Advanced Algorithms, Software, and Applications,” which will address problems related to portable computational libraries. The third proposal provides a unique opportunity for the Physics Laboratory to have an impact on the federal High Performance Computing and Communications (HPCC) initiative.

The panel is particularly encouraged by indications of improved interlaboratory activity. Such activity includes a joint proposal for evaluating reference data with the Chemical Science and Technology Laboratory. The proposed data evaluation would be important to most industrial support activities authorized by HR 4848, the Technical Competitiveness Act, which created NIST from the National Bureau of Standards in 1988.

The laboratory proposed an exciting “umbrella” initiative on advanced optical technology, involving staff from many of its divisions. NIST is the only laboratory in the United States where the broad range of necessary expertise exists in optical measurement and instrumentation techniques to pursue the proposed advances in optical technology. NIST's expertise spans the electromagnetic spectrum from the infrared through the ultraviolet and up to soft and hard x-rays. The proposal includes developments in advanced optical devices, x-ray technology, infrared technology, display technology, and optical manufacture and measurement.

In its fiscal year 1992 program review, the panel was briefed on the changing scene in international standards and laboratory accreditation, especially developments in the European Community (EC). According to EC-92 regulations, U.S. industry must register, accredit, and comply with international standards such as those set down by the International Organization for Standardization (ISO) in order to have its products accepted by EC member nations. The quality of products made in the United States must be demonstrated to comply with these regulations. The panel expressed considerable: concern in its fiscal year 1992 assessment report that the United States was not prepared to meet this challenge for certification of products and accreditation of processes and laboratories. This year (fiscal year 1993) the panel was briefed by the chief of NIST's Calibration Program on NIST's progress in meeting the EC-92 and National Laboratory Accreditation Program challenges. Progress has been made, particularly in the area of laboratory accreditation, where three new hires were made. ISO issues are particularly important for industries needing optical and radiometric calibrations and

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

metrological standards. The panel discusses these issues further in the assessment of the Radiometric Physics Division.

In discussions with a number of scientific staff members, panel members raised concerns about the efficiency and usefulness to the Physics Laboratory of the Manufacturing Engineering Laboratory's Fabrication Technology Division machine shops. NIST is being asked to respond to the needs of U.S. industry and therefore must be able to rapidly make devices for specialized use. Adequate and responsive machine shop services are critical. In response to its inquiries, the panel was given a report by an internal NIST committee that reviewed this matter in fall 1992. The panel endorses the internal report's main conclusions and recommendations, which are as follows: (1) Research on computer-aided design/computer-aided manufacturing (CAD/CAM) should be separated from services provided to shop users. (2) The important role of the instrument maker to the cadre of expertise at NIST, which historically has helped to make its scientific research unique, should be renewed. (3) The number and quality of small “contact shops” reporting to and controlled by the divisions should be increased. (4) Engineering Services, which presumably does design and drafting work for various NIST programs, should be eliminated.

In its fiscal year 1992 assessment the panel expressed concern that metrological standards, especially those for length and mass, were not receiving the level of attention needed to serve the high-technology industries of the next century. Because length is now derived from the standard second using the defined velocity of light, there is a need for a practical and transferable manifestation of this definition. This issue is discussed further in the panel's assessment of the Time and Frequency Division.

With regard to career development and personnel matters of its technical staff, the Physics Laboratory is strengthening its diversity. Last year, it hired two African Americans and one woman among its 13 new National Research Council (NRC) postdoctoral fellows. The panel also recognizes that NIST has additional opportunities, and perhaps responsibilities, to better use the special talents of Russian and Eastern European scientists.

In summary, the panel finds that the Physics Laboratory is very productive in a broad spectrum of research and development, including fundamental physics research, applied physics, instrumentation and metrological standards work, services to industry, and technology development.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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ASSESSMENT OF DIVISIONAL PROGRAMS
Electron and Optical Physics Division
Far Ultraviolet Physics Group at the Synchrotron Ultraviolet Radiation Facility

Most noteworthy among the activities of the Far Ultraviolet Physics Group that manages the Synchrotron Ultraviolet Radiation Facility (SURF) was completion of the alteration of SURF's physical layout. The removal of a wall, relocation of the power supply for the ring, and rewiring of the electrical supply to the experimental stations provides a much-needed facility improvement. The x-ray spectrometer is awaiting installation, as is discussed in the section below on the Photon Physics Group.

With regard to efforts on the various beamlines around the SURF ring, installation of new slits on the 2-m normal incidence monochromator (NIM) is complete and operational, and a University of Nebraska researcher is setting up a gas-phase experiment, taking advantage of the new areas for guest users that were allocated as part of the facility reconstruction. The assignment of a staff member to work with the University of the District of Columbia on the 6.65-m NIM should help move this program along. This instrument should be able to deliver a highly accurate (probably the most accurate to date) high-resolution determination of the absorption cross section of N2.

Progress is being made in the development and analysis of silicon detectors (as discussed in the panel's fiscal year 1992 report). This work accompanies the progress of industrial collaborators in fabricating these detectors. A beamline is used to calibrate detectors for the National Aeronautics and Space Administration's use.

The spectrometer necessary for using the SURF facility as a primary radiometric standard is now functioning. Calibration comparisons with a thermopile have given good results. Since one area of the laboratory is now responsible for radiometric calibration standards at all wavelengths, an overlap of optical and infrared wavelength calibrations is possible for wavelengths where calibrations were previously weakest.

One of the most desirable characteristics of the SURF facility is the extent to which its radiation can be described analytically, making SURF radiation extremely useful for experiments using vacuum ultraviolet (VUV) optics. SURF's comparative advantage over more recently constructed synchrotron radiation sources is its broad spectrum of wavelengths of light suited for research and calibrations. SURF is more than competitive in its absolute flux reference capabilities. Moreover, it is extremely cost-effective. For these reasons, SURF can continue to occupy a useful niche among the nation's storage rings.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×
Electron Physics Group

The Electron Physics Group is recognized worldwide for its innovative approaches, its path-breaking research, and its outstanding technical skills and accomplishments. Its main areas of research are electron-surface interactions; electron microscopy; surface, thin-film, and multilayer magnetism; laser-focused atom deposition; electron-polarization phenomena; electron optics and instrumentation; and electron-interaction theory.

The group's major accomplishments during fiscal year 1993 have been in magnetic properties of surfaces and, in particular, phenomena related to magnetic (micro) structure. Highlights include the following:

  • Scanning electron microscopy with polarization analysis (SEMPA) studies of the antiferromagnetic ordering of chromium thin films;

  • SEMPA studies of the domain structure of cobalt single crystals;

  • SEMPA studies of the structure of domain walls at surfaces;

  • SEMPA studies of the nature of coupling between two ferromagnetic films--iron, in particular--separated by a thin layer (or a shallow wedge) of a normal metal, in particular, chromium and silver;

  • Deposition of chromium atoms on a silicon surface in a well-defined pattern--thin, 50-nm-wide lines spaced periodically by 213 nm--controlled by a laser (laser focusing);

  • Scanning tunneling microscopy (STM) studies of the electronic properties of cesium structures--one-, two-, and three-dimensional--deposited on indium antimonide surfaces;

  • STM studies of the initial stages of film growth, in particular, iron on iron and chromium on iron;

  • Initial stages of the development of a scanning tunneling microscope with magnetic sensitivity;

  • Studies of polarized electron-atom scattering, in particular, scattering from sodium atoms that were spin polarized by optical pumping;

  • Theoretical studies of exchange coupling in magnetic heterostructures, in particular, magnetic layers separated by a nonmagnetic spacer; and

  • Theoretical studies of the isotope effect in high-temperature superconductivity and the constraints it imposes on the various theoretical models.

The group is well balanced with respect to age distribution, theoretical versus experimental effort, and basic research versus instrumentation development. Despite its considerable strengths, the group could benefit from longer-range planning, a steady budget, and a steady influx of postdoctoral fellows.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×
Photon Physics Group

A major accomplishment of the Photon Physics Group since the panel 's fiscal year 1992 assessment is the completion of a monochromator (including the toroidal gradient mirrors) for the NIST/Advanced Research Projects Agency (ARPA) soft x-ray reflectometry facility, which improves wavelength and spatial resolution and expands wavelength coverage. The next step is to construct and commission a new reflectometer chamber that permits measurements on large optical components (up to 35 cm in diameter). A valuable radial scanning mode will also be made an option. Joint NIST, ATP, and ARPA funding for this program attests to its perceived value to the x-ray community for “at wavelength ” analysis of optical elements.

Work utilizing the x-ray fluorescence spectrometer at the National Synchrotron Light Source is continuing, although it is anticipated that these experiments will move to the Center for Advanced Microstructures and Devices in Louisiana in the near future. The greater propagation in matter of photons produced in x-ray decay allows probing of matter at greater depths. Also, the probing is less sensitive than longer-wavelength probing to the sample's surface features. Measurements to date have been primarily for use in the analysis of high-critical-temperature (high-Tc) superconductors. The panel supports future plans that call for measurements to analyze buried interfaces, with more emphasis on the solid-state physics phenomena. A similar spectrometer is being constructed for one of the beamlines at the new Advanced Light Source at the University of California, Berkeley.

The continuing multiphoton process experiments are an excellent mix of applied and fundamental physics. One achievement since the fiscal year 1992 assessment was the determination of the configuration-dependence of the alternating current Stark shifts in calcium. One discovery from these measurements was that the level shift in a high field can be up to half as large as the ponderomotive shift. Experiments on calcium are expected to continue in an effort to determine a suitable multiphoton excitation mechanism, which could lead to an isotope enrichment program. A cost-effective calcium isotope separation scheme is needed for medical research; calcium isotope experiments are essential in the study of bone decalcification caused by extended periods of weightlessness during space travel. This effort is being conducted in cooperation with a small industrial company.

Measurements on two-photon processes in helium are continuing, although conducted largely by a postdoctoral research fellow. The helium experiment is a potentially important fundamental project. The high-precision calculations of the ground state of neutral atomic helium have never been tested against a high-accuracy, high-precision laser experiment. Since helium is the simplest and the most fundamental multielectron

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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system, this experiment offers the possibility of a discovery of profound importance to physics.

Atomic Physics Division
Atomic Spectroscopy Group

Atomic data generation and evaluation continue to be an important part of the mission of the Atomic Spectroscopy Group. Recent accomplishments include the improved measurements of wavelengths for the prominent spectral lines of Cr XVI to Cr XXII. The spectra of transition metals are of particular interest to the fusion community. In support of the VUV spectroscopy being carried out by NASA Goddard using the high-resolution spectrometer on the Hubble Space Telescope, the group has obtained high-accuracy laboratory wavelength data for the different isotopes of Hg III. The laboratory measurements enable the proper interpretation of the Hubble data, which in turn will have a significant impact on various theoretical models of young, hot stars. A general thrust of the spectroscopy research has been to extend the availability of high-quality data to more highly ionized systems and heavy elements, where information is sparse or nonexistent. The group has used a variety of sources of experimental spectra, such as laser-produced and magnetically confined plasmas, and will soon have access to the electron beam ion trap. This novel ion source, which is discussed further in the assessment of the Plasma Radiation Group, will provide new opportunities to obtain high-resolution spectra of highly charged ions in an environment free of plasma effects. The productivity of the Atomic Spectroscopy Group is reflected in its number of high-quality publications and the receipt of the 1992 William F. Meggers Award by one of its members.

Collaborations with external organizations appear to have strengthened since the panel's fiscal year 1992 assessment. The group plans to develop a computer-accessible database for atomic energy levels, transition probabilities, and lifetimes and to network it to the Astrophysical Data System supported by NASA and to ALADDIN, which is sponsored by the International Atomic Energy Agency and the Department of Energy. This effort is timely in view of the current federal emphasis on high-speed computer networks as components of an “information superhighway.” Computer-accessible spectroscopic data would also benefit U.S. industry. One current need is for atomic data involving rare-earth elements for the development of new lighting technologies. The group is a valuable scientific resource for other federal agencies with specific atomic data needs.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Atomic Radiation Data Group

The Atomic Radiation Data Group develops fundamental atomic theory and maintains state-of-the-art computational capabilities for atomic phenomena. Experimental studies are carried out to resolve discrepancies in the theory and thus increase understanding of the underlying atomic physics. Research focuses on effects of relativity in electron-ion collisions and on the quantum electrodynamical theory of electronic structure. A recent accomplishment is the calculation, with unprecedented precision, of nuclear size effects on the self-energy contribution to energy levels of heavy, highly charged ions. The Atomic Radiation Data Group is small, and the panel believes it could benefit from having an NRC postdoctoral fellow. Past concerted efforts to recruit the best available young atomic theorists from good schools have not been successful.

This group also assists in critical evaluations of atomic data for the Atomic Energy Level Data Center and the Data Center on Atomic Transition Probabilities and Line Shapes. During fiscal year 1993, the group added a part-time scientist with major responsibility for building a database readable from widely available platforms such as personal computers and workstations. This effort is parallel to the networking of the Atomic Physics Division's critically evaluated spectroscopic data to NASA's Astrophysical Data System.

The Atomic Radiation Group shared in the development of an interdivisional proposal for the federal HPCC initiative. Should this proposal be funded in fiscal year 1994, it would provide the group with an opportunity to exploit massively parallel computers for frontier atomic structure calculations and to make a major contribution to computer-based dissemination of critically evaluated atomic databases. The group could also expand the scope of its work to include computational physics, an area that appeals to many young scientists.

Plasma Radiation Group

Significant progress has been made by the Plasma Radiation Group during fiscal year 1993 on the development of the electron beam ion trap (EBIT). EBIT is now almost fully assembled, and component testing is well under way. The development of EBIT is extremely important in NIST's continuing world leadership in basic atomic spectroscopy and to its becoming a world leader in the basic atomic spectroscopy of highly ionized atoms. Spectroscopy of highly ionized atoms is important for diagnosing fusion plasmas and for fundamental tests of plasma theory. NIST's work in this field is now being performed using laser-produced plasmas and Tokamak plasmas at remote sites. Along with greater productivity due to an in-house capability, EBIT has the potential to provide sharp, unperturbed spectral lines that are unaffected by the turbulence and the high collisional rates found

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

in laser-produced plasmas. The Plasma Radiation Group plans to broaden its research using EBIT to include both atomic spectroscopy and materials research involving surface modification using highly charged ions. EBIT can be applied to a mix of pure and applied science that is likely to lead to more stable funding for the group. EBIT will probably become operational within the next several months; however, some time will be required to “tune up” and operate the machine.

Progress was made during fiscal year 1993 in characterizing the radio-frequency reference reactor conceived by scientists at the Gaseous Electronics Conference (GEC). The GEC reference reactor has several purposes. Low-temperature radio frequency plasmas, which are used extensively for etching and deposition during the fabrication of integrated circuits, are poorly understood and are often difficult to reproduce. The low-temperature plasma research community is using the GEC reference reactor to learn much about the control of experimental factors necessary to replicate well-defined plasmas. The Plasma Radiation Group is refining radio frequency plasma measurement techniques by reproducing and checking diagnostic measurements in independent laboratories. The well-defined, well-diagnosed plasma in the GEC reference reactor is providing benchmark data for comparisons with models of complex low-temperature plasmas. The recipe for reproducing a well-defined, well-diagnosed low-temperature plasma will be useful in the development of new methods for diagnosing plasmas. The spectroscopic observations of highly nonthermal hydrogen atom kinetic energy distributions constituted a significant milestone in the program.

The absence of a program leader for the GEC Reference Reactor Program slowed progress during fiscal year 1993. This group is uniquely qualified to contribute absolute emission and absorption measurements to the nationwide GEC Reference Reactor Program. Other parts of NIST are providing mass spectrometry and chemical sciences support for the program, which could be strengthened further by collaboration on modeling. For example, SEMATECH, the consortium of U.S. semiconductor manufacturers, is launching a major 3-year initiative on the modeling of low-temperature plasmas used in semiconductor processing. Because the physics and chemistry of such plasmas are so complex, a close interplay between experiment and theory is essential for rapid progress. Low-temperature plasma physics, plasma processing, and related areas are important in manufacturing technology. The GEC reference reactor has been replicated in numerous research laboratories, including those of NIST, AT&T Bell Laboratories, and Sandia National Laboratory. In addition to conducting its experimental work on the GEC reference reactor, the group has edited and published a newsletter on reference reactor studies.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×
Laser Cooling Group

The Laser Cooling Group does interesting experiments with limited internal resources and has been successful in attracting excellent young scientists and obtaining outside resources. Recent experiments to obtain the stiffness of the potential formed by the interfering laser beams used in cooling and trapping rubidium atoms by observing the size and magnitude of phase-modulated side bands are an interesting application of quantum mechanical phenomena. The group has also demonstrated the selective trapping of each of the nine isotopes of xenon. Recently the group has been developing another type of atomic trap using atom-reflecting mirrors, in which the atom is reflected from a dielectric surface and forms an evanescent light wave by total internal reflection within the dielectric. This trap depends on the coupling between this light wave effect and the force of gravity.

The work of the Laser Cooling Group has a number of symbiotic applications, including the following:

  • Cesium fountains are a very good tool for assessing systematic error in estimations of the accuracy of the second based on 133Cs.

  • Cooling by lasers is a vital tool for many other branches of spectroscopy.

  • Trapping with microwaves, a new technique, provides an attractive prospect for achieving Bose-Einstein condensation of hydrogen, a long-sought-after phenomenon, and has a fundamental bearing on quantum statistical mechanics.

Molecular Physics Division

The Molecular Physics Division continues to do outstanding scientific work, as demonstrated by the number of honors that have accrued to its members. The most recent include a fellowship in the American Association for the Advancement of Science and the 1992 Sigma Xi Young Scientist Award. The division's ability to attract outside funding is also strong; for example, the High-Resolution Spectroscopy Group attracted two new contracts and two renewals, and the Molecular Dynamics Group continues to receive support from other government agencies such as the Air Force and the Department of Energy.

Both the High-Resolution Spectroscopy Group and the Molecular Dynamics Group have a number of state-of-the-art facilities and are performing unique experiments at the frontiers of their fields that have potential for technological impact. These experiments include investigations of fundamental chemical processes that are important in the manufacturing of solid-state devices, studies of gas-phase reactivity and energy relaxation that have applications in environmental issues related to the

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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atmosphere, investigations of structure-reactivity relationships for prototype molecular systems that are of importance in biological systems, and studies of energy flow and chemical reactions in every phase of matter that can be expected to have an impact on minimizing the use of energy.

Molecular Dynamics Group

The Molecular Dynamics Group's scientific achievements rank at the top of the field of chemical dynamics, especially in the study of dynamic processes on surfaces and in liquids and in the investigation of gas-phase molecular photodissociation dynamics. It has become one of the best-equipped picosecond/femtosecond laser laboratories in the world. To maintain its cutting-edge scientific effort in this competitive and fast-moving area, the group will need to continually update its laser hardware and develop new time-resolved spectroscopic techniques. Equipment purchased and built over the past 2 years will allow this outstanding group to continue its forefront scientific work.

The Molecular Dynamics Group focuses on the most significant topics in chemical dynamics, including the following: (1) photochemical studies of chemical reactions of importance to atmospheric, environmental, and combustion chemists, (2) studies of dynamic vibrational processes for molecules adsorbed on surfaces in which the rate of coupling between metal surfaces and adsorbed molecules has been investigated for the first time, and (3) investigations of metal carbonyl photochemistry in liquid solutions where reactions with the solvent bath molecules occur rapidly and can affect the photochemical reaction path.

This group has studied the reaction of O (1D) atoms with isotopically enriched H218O and Shown that under ordinary “bulb” conditions in the gas phase the reaction produces two species of OH radicals with very different energy content. The higher-energy form of OH appears to be formed by a direct reaction and carries away a disproportionate share of energy in rotation and vibration. All the evidence suggests that this reaction, when occurring as a bimolecular encounter, proceeds through a complex with lifetime of less than 100 femtoseconds. Experiments carried out under supersonic expansion conditions, and beginning with the van der Waals species O3·H2O, show OH energy profiles that are astonishingly different from those obtained in experiments carried out under bulb conditions. Here the species begin as a weakly bound complex, forcing the reactive species to be in close proximity to each other. In the van der Waals experiment, the OH fragments carry away much less energy than in the bimolecular reaction, and the kinematics of the process are quite different. One possible explanation of these differences is that the cluster reaction converts O (1D) to O (3P) very early in the reaction mechanism, so that the important reactive species is O (3P), not O (1D). It is commonly believed that O (3P) reacts by abstraction,

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

whereas O (1D) reacts by insertion. These kinds of studies are among the most advanced in the chemical dynamics area, providing information about chemical processes that begin with preoriented reactants. Results from these experiments and future planned studies on O (1D) + CH4 are expected to provide a great deal of insight into the mechanistic dynamics of these processes, which are important for detection of atmospheric OH radicals and for understanding the driving forces behind chemical reactions of atmospheric importance.

In a novel experiment conducted since the panel's fiscal year 1992 assessment, the group investigated the coupling between a metal surface and an adsorbed species. Hot electrons were created in a metal substrate, and the flow of energy from the metal to an adsorbed CO molecule was observed using transient infrared absorption spectroscopy. It is unknown whether the mechanism for this coupling involves hot electrons coupling directly to the adsorbate, or first cooling by energy transfer to phonons in the metal. The latter mechanism would approximate a generalized thermal coupling of adsorbate vibration to the metal substrate energy reservoir. The time scale found for this back coupling in the case of CO on platinum is only 2 picoseconds. This rate approaches the vibrational mode frequency of the frustrated platinum-carbon translational motion between the metal and the adsorbate. This new line of investigation is providing a number of “firsts” in determining the mechanism for energy flow between metal surfaces and adsorbed molecules. This work is fundamental as well as practical, because the Pt/CO system serves as a prototype for the investigation of a number of catalytic systems.

The gas-phase and surface photodissociation studies performed in the past by this group were among the most elegant and well conceived of their time. The group has now moved into the area of solution-phase photochemistry by investigating the photolysis of metal carbonyls in liquids. For example, the group's latest experiments involve the photolysis of metal dicarbonyls that have a ligand such as cyclopentadiene attached. In solution the reactants are found to disappear rapidly, but the infrared absorption characteristic of some of the product species shows up only slowly, indicating a metastable species somewhere in the reaction path. Current experiments are investigating the role of the solvent in these superfast chemical reaction processes. Because the time scale and the transition states that characterize these kinds of solvent insertion reactions are currently unknown, this work constitutes another scientific breakthrough and unique contribution, typical of the group's work over the past few years.

The overlap of the scientific concepts relevant to different programs in the Molecular Dynamics Group, whether in the gas phase, in clusters, in liquids, or on surfaces, is impressive. Gas-phase photochemistry often provides clues to the mechanisms observed in surface and liquid-phase photochemical reactions, and

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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energy relaxation processes occurring both in the gas phase and in clusters are often remarkably similar to corresponding processes on surfaces. Thus the group's program is remarkable for both its diversity and its intellectual cohesiveness. The origin of the successes of this scientific effort can be found in the first-rate intellectual leadership of the group, its excellent and continually improving equipment inventory, and the technical virtuosity and strong work ethic of its members.

High-Resolution Spectroscopy Group

In just the past 2 years, the High-Resolution Spectroscopy Group has developed a number of well-focused programs that address forefront problems of molecular spectroscopy and dynamics. The topics chosen are a good balance between cutting-edge research and issues closely related to national needs. The group's technical activities include (1) infrared spectroscopic studies of environmentally important molecules; (2) spectroscopic studies of energy storage and dynamics in molecules; (3) microwave and infrared studies of hydrogen bonded complexes, which are related to fundamental questions in biochemistry and chemical catalysis; (4) spectroscopic studies of unstable molecules at low temperatures; and (5) database compilations for the scientific and industrial communities.

This group has developed a high-pressure, low-temperature multipass infrared cell coupled to a Fourier transform spectrometer. This facility, the only one of its kind in the world, can be expected to offer unique capabilities for environmental studies and to attract international scientists working on research related to global warming and the ozone hole. A number of programs that make use of this device have already been started, including measurements of both N2 and O2 spectra and some linewidth measurements in CO2. The group is also continuing its long-term effort in high-resolution spectroscopy using both diode lasers and a unique laser difference frequency spectrometer. The problems under study are related to a number of questions in atmospheric chemistry, including acid rain formation and ozone destruction. The computer code used to design the multiple-pass cell is a state-of-the-art optics code and may offer additional opportunities for technology transfer.

In the area of energy transfer dynamics, this group has undertaken an international experimental and theoretical collaboration to determine the features of a molecule that control its intramolecular vibrational relaxation. The group has made a number of breakthroughs in a study of the prototype molecule acetaldehyde and has come up with a promising new method for studying dark states using Stark spectroscopy. These issues are at the heart of one of the most important problems in chemical dynamics today, the role of energy transfer and

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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intermode vibrational coupling in controlling chemical reaction processes.

The High-Resolution Spectroscopy Group continues its leadership in the study of weakly bound molecular complexes with studies of the methanol-water and methanol-methanol systems, undertaken originally because of their importance in methanol-to-gasoline conversion. Unexpected results have been obtained that may affect not only our understanding of chemical catalysis, but also the current view of conformational arrangements in biomolecules, an extremely active area of interest in computer modeling of large molecular structures. The group has nearly completed the construction of a state-of-the-art Fourier transform microwave pulsed beam spectrometer. This new machine should provide substantially improved data acquisition capabilities and the stability required to make supersensitive experiments feasible. The group has tackled some tough problems in mapping out thermal stability and reaction pathways for energetic molecules and has obtained structural properties of freon substitutes. This kind of information could have a significant impact on technological issues such as predicting structure-function relationships for a variety of freon replacement candidates.

The group's work on radicals and ions in low-temperature rare-gas matrices continues to be outstanding, and additional equipment for visible and ultraviolet spectroscopy has enabled the group to obtain details of molecular electronic spectra that complement the already impressive infrared spectral data obtained in the past.

Finally, the High-Resolution Spectroscopy Group continues to provide a significant service to both the scientific and the industrial communities by producing a number of critically edited data compilations. The most recent of these include a compilation of visible and infrared spectra of free radicals, a completed volume of critically evaluated molecular spectra (the third volume in a series), and a microwave compilation of species of interest in astrophysical studies.

The group continues to involve a large number of guest workers in its programs. One constructive program enables a number of Russian scientists to visit NIST for collaborative research.

Overall the laboratory is well equipped and well positioned to undertake a key role in environmental science programs that build on its base expertise in gas-phase, high-resolution molecular spectroscopy. The group has attracted significant external funding and stabilized its financial problems; however, the panel believes that additional base funding will be required to secure its long-term future.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Molecular Theory Group

The Molecular Theory Group continues to do excellent research and is well regarded in the international community. The group has taken a leadership role in two emerging fields, both of which involve the interaction of laser light with atoms and molecules, namely, collisions of laser-cooled atoms and the photodissociation of molecules by ultraintense laser pulses. In spite of its small size (two professional staff members) the group has been very productive, making effective use of guests, contractors, and numerous outside collaborators.

The ability to cool, trap, and optically manipulate atoms has become a rapidly developing and important area of experimental and theoretical research. It offers prospects for major improvements in time and frequency standards and many other applications of physical phenomena. It is crucial to understand the collisions of laser-cooled atoms for two reasons: first, such collisions affect the properties of beams and other sources of cold atoms for intended applications and, second, the collisions themselves can be controlled using optical laser light. The Molecular Theory Group has carried out pioneering work in this area by developing new ideas and techniques required to predict and interpret the collision rates of extremely cold atoms at temperatures below 0.001 K. The group has developed a new method based on the optical Bloch equation to describe the unusual physics associated with optical excitation and decay during ultraslow collisions. The method has been used to predict the behavior of various atoms in magneto-optical traps, and these predictions are being experimentally tested in several laboratories. The group has collaborations with a number of experimentalists working in this field at other NIST laboratories and at the University of Maryland and the University of Texas, and has received widespread recognition. For example, a member of the group co-organized a workshop on collisions of laser-cooled atoms at the Harvard-Smithsonian Institute of Theoretical Atomic and Molecular Physics and published a review article on the subject in Advances in Atomic, Molecular, and Optical Physics.

The group has also done important work on the response of molecules to short, intense pulses of laser radiation. Independent models, one based on time-dependent and the other on time-independent collision theory, were integrated, and the competition between photodissociation and photoionization has been examined for simple diatomic molecules. The group's theoretical advances have stimulated new experiments by predicting unusual effects, such as “population trapping,” wherein molecules survive short but very intense laser pulses without breaking apart. Current efforts are focused on the “coherent control” of the photodissociation of HD+ by phase-locked, two-color laser fields. The concept of coherent control of molecular reactions, in which the relative phases of two

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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lasers are used to actively alter the branching ratio for different product channels, has the potential for revolutionizing the field of laser-induced chemistry. It also may have a significant technological impact on isotope separation, selective destruction of pollutant molecules, and production of novel chemical species.

The group's current research portfolio, which balances development of new methodology and computations on atoms or molecules of interest, provides a good opportunity for participation in the federal HPCC initiative. The accurate computational treatment of the quantum dynamics of many-body systems in external fields is a grand-challenge-type problem, and it could greatly benefit from the utilization of massively parallel platforms.

The Molecular Theory Group is an asset to the Physics Laboratory both because of its excellent scientific output and because of its high visibility in the outside community. The group has been successful in attracting junior and senior collaborators from outside NIST and has made effective use of NIST and office of Naval Research funding to support such collaborations. The panel notes that the addition of another staff scientist to the group would greatly enhance its effectiveness and ability to contribute to the NIST mission, especially in the areas of high-performance computing and new technology development.

Radiometric Physics Division

The Radiometric Physics Division promotes accurate and useful optical radiation measurements in the ultraviolet, visible, and infrared spectral regions. The division develops, improves, and maintains the national standards and measurement techniques for radiation thermometry, spectroradiometry, photometry, and spectrophotometry. It disseminates these standards by providing measurement services to customers requiring calibrations of the highest accuracy. The division also conducts fundamental and applied research to develop the scientific and technical basis for future measurement services. The division has been reorganized into three groups, each managed by a group leader who reports directly to the new division chief. The three groups are the Infrared Radiometry Group, the Thermal Radiometry Group, and the Detector Metrology Group. Each group operates under a program structure that allows for well-defined technical activities to be carried out with clearly marked responsibilities.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Infrared Radiometry Group

The Infrared Radiometry Group is pursuing a number of interesting new and ongoing programs. The low-background infrared radiation (LBIR) facility is proving to be a workhorse for spectral calibration, with another upgrade program on the way. The ambient background infrared (ABIR) facility is developing into a first-rate infrared spectral detector calibration facility by the extension of its range from 1.8 to 25 µm. New possibilities for measurements of optical properties of materials using the hemiellipsoidal diffuse reflectance apparatus are evident. At the same time, advances are being made with high-temperature superconductors to improve the nonequivalence radiation conditions of cryogenic radiometers. The quality of this group is manifested in the many first-rate papers generated since the panel's fiscal year 1992 review.

The LBIR facility serves as a secondary standard calibration system for radiometry and is directly traceable to the high-accuracy cryogenic radiometer (HACR). It provides primary calibrations for customers requiring high-accuracy, high-sensitivity infrared sensors for both broadband and spectral response in a low-background environment. An absolute cryogenic radiometer, the heart of the system, is capable of measuring between 20 nW and 100 µW of radiant power.

A new thrust will be the development of a spectral calibration capability. To facilitate this new requirement, a cryogenic blackbody with six apertures ranging from 250-µm to 2-mm diameter has been constructed and is being incorporated into the operation. Together with several filters, this blackbody serves as a general source for detector calibration and optical materials characterization. Additional efforts are being expended toward the measurement of total emittance to within accuracies of about 1 percent. This work is in support of and partially financed by the Midcourse Space Experiment, which requires these parameters for black spheres.

The ABIR detector calibration facility provides detector responsivity calibration in the spectral range from 200 nm to 1.8 µm. A concerted effort is under way to extend it farther into the infrared region, up to 25 µm. Inclusion of an integrating prism/grating monochrometer, together with a cryogenic bolometer traceable to the HACR, will allow responsivity measurements. This promises to become a first-rate infrared detector spectral calibration facility. Detailed experiments indicate the bolometer instability as well as the nonlinearity of the 5-mm-diameter sapphire disk to be less than 1 percent over a laser power range of 10-7 to 10-2 mW. Further improvements are planned with the bolometer before final integration into the spectral facility, which promises to yield nonlinearity accuracies of 2 percent or better for the whole system.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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A unique and interesting hemiellipsoidal apparatus has been assembled within the Infrared Optical Properties of Materials Program for diffuse reflectance measurements. The reflectance is measured off material surfaces and essentially covers angles between 0 and 90°. This system should be operational in the near future, and the goniometer at laser wavelength is available for measurements at this time.

New polystyrene standard reference materials have been developed for the calibration of spectrophotometer wavelength scales in the mid-infrared range. A total of seven wavelengths are available for the calibration of Fourier transform infrared spectrometers, each with monochromaticity of about 0.5 cm-1. This capability is complemented by a secondary standard reference material for six additional wavelengths at accuracies of about 1.0 cm-1 each.

In order to extend the power levels of the radiometer operating at liquid helium temperature below 20 nW, a superconducting kinetic-inductance absolute cryogenic radiometer (AKACR) has been constructed within the Advanced Concepts of Radiometry Program. The high-Tc superconducting-film-based radiometer has yielded a nonequivalence due to temperature fluctuations in the cavity of 0.003 percent at liquid helium temperature, which is about a factor of 7 better than the conventional design. The goal is to extend the AKACR up to liquid nitrogen temperature, 77 K, by using the new high-Tc superconducting materials. It will require investigations of optical properties for 1 to 1000 µm at various temperatures.

An interesting program under consideration is parametric down conversion, a concept that constitutes old physics with new ideas. In essence, laser light incident onto a parametric crystal results in photon pair productions with the two photons separated by fixed angles. Photon counting techniques are then used as absolute calibration standards. The implications of this program are still unknown.

Thermal Radiometry Group

The Thermal Radiometry Group has several exciting programs under way. An intercomparison program, using copper blackbodies, has been started with the Japanese National Standards Laboratory. Ideally, this will give the United States an indication of Japan's primary radiometric capabilities. Environmental issues are being tackled on several fronts. Of special interest are recent ultraviolet monitoring, measuring, and calibration in support of NASA, the Department of Agriculture, and the Environmental Protection Agency. Observation of ozone levels as well as climatic changes will require further detailed involvement by division personnel. The group's goal of standardizing all ultraviolet sensors should be of great value to the user community.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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The group's thermal imaging laboratory can calibrate infrared detecting devices that operate in the temperature range from 0 to 100°C and characterize temperature and temperature differences of infrared blackbody sources and radiometers. A high-temperature blackbody was developed and recently characterized at 2500 and 2800 K. Tests have been completed for radiance and irradiance uniformity using special software to stabilize the output of the blackbody to less than 0.05 percent. The next phase of the program will involve using filter radiometers to characterize the pyrographic blackbody radiator at 3000 K for use in realizing the NIST spectral irradiance scale. The panel recognizes the importance of this program and observes that it is underfunded.

The development of several blackbody sources that will allow radiance temperature measurements to be made over the range of 0 to 3200° C is near completion. This effort has involved the development and characterization of cesium and sodium heat-pipe blackbodies; a mercury unit is also under consideration. The development of a low-temperature graphite blackbody is under way while the high-temperature unit, which is to operate at up to 3000°C, is being refined. These blackbodies will become the basis for an expanded capability in the Radiometric Physics Division's thermal imaging radiometry work.

Additional work has recently been started to investigate the use of Fourier spectroscopy for radiometric purposes. The rationale is that it may be possible to use low-resolution Fourier spectroscopy to study the emissivity of blackbodies and the output of miniarc infrared sources.

The Radiometric Physics Division is currently building instrumentation and preparing procedures necessary for characterizing the solar ultraviolet instrumentation to be deployed by the Department of Agriculture. NIST, with Department of Agriculture support, will also operate a UV-B spectroradiometer intercomparison, scheduled for fall 1993. The division is involved with the Environmental Protection Agency, NASA, and the National Oceanic and Atmospheric Administration (NOAA) on a number of different programs related to global climatic change initiatives. The division makes critical contributions to the missions of other agencies by providing the scientific knowledge and advances in metrology necessary to ensure accurate measurements for decision making and regulation.

Implementation of a calibrated photometric detector for monitoring the output of spectral irradiance lamps and as a standard on the Facility for Automatic Spectroradiometric Calibrations (FASCAL) was successful. The detector provided a link between the NIST detector scale based on high-accuracy cryogenic radiometer measurements and that based on NIST's spectral irradiance measurements. The detector not only has provided timely stability data but also has revealed that the two sets of measurements are in agreement to within 0.5 percent for the 400- to 800-nm wavelength range. The division is purchasing

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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new argon and deuterium lamps for FASCAL and cites the availability of the facility as critical for U.S. industry.

Recent changes in the organization of the Radiometric Physics Division have resulted in the assignment of several spectrophotometric measurements to the newly created Thermal Radiometry Group. The specific areas are transmittance, reflectance, and the bidirectional reflectance distribution function. All of these measurements are now grouped under the Optical Properties of Materials Program. A major effort is under way to redesign the high-accuracy spectrophotometer. A thorough analysis of the existing device has been completed. The next step will be to bring on-line two instruments to cover the entire range for transmittance and reflectance measurements from 0.2- to 20-µm wavelengths. The Optical Properties of Materials Program is also poised to meet several new challenges in time-dependent optical measurements and microoptics technology. The panel agrees that the above changes are a step in the right direction. The Radiometric Physics Division is seeking to better align its programs with customer needs through closer coordination with customers.

Detector Metrology Group

A wide variety of programs is under way in the Detector Metrology Group; highlights are discussed below. Outstanding progress is being made toward realizing several radiometric scales based on detector standards and thereby directly traceable to the high-accuracy cryogenic radiometer (HACR). Progress toward improvements in quality and compliance with existing requirements as listed in international standards such as ISO Guide 25 is evident and encouraging. Advances with tunnel trap detectors should yield improvements in accuracy for radiometric scales and constitute a significant technology application. Several other high-technology efforts are in progress, such as high-precision aperture measurements, improvements in realizing the International System of Units (SI) unit of the candela to 0.4 percent, with the goal of attaining 0.1 percent in the future, and realization of luminous flux and spectral flux on absolute scales. This broad base of high-technology programs has resulted in numerous first-rate publications since the panel's fiscal year 1992 assessment. The group's program is on target and supported enthusiastically by the professional staff.

Improvements in the HACR automatic data acquisition system have resulted in much faster measurement rates. Improvements in the HACR reduced the time required for a measurement by 50 percent. The nitrogen fill and tunnel trap carousel device are being automated to permit up to 12 measurements to be made in a 24-hour period. By switching from optical to electrical heating techniques and by using predicted asymptotic temperature behavior, routine measurements are now accomplished in 2 to 3 minutes instead of 2 to 3 hours.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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The HACR's new laser-based comparator system promises to be of extreme importance for outside customers. This system will allow comparisons of customer units against one or more trap detectors, which in turn will have been calibrated with the HACR. The HACR was also recently used to determine the absolute spectral responsivity and external quantum efficiency of light-trapping silicon photodiode packages. Results were compared with measurements made in the NIST Spectral Comparator Facility, and agreement was found to be better than 0.1 percent at 633 nm and 0.25 percent at 442 nm.

The HACR is starting to serve as the base for the NIST-maintained scales of spectral radiance, irradiance, and absolute detector spectral responsivity. This integration will improve the stability and measurement uncertainty of each scale.

The panel endorses the assignment of a new HACR program leader but is concerned about the lack of a detailed plan or road map that shows the time line and tasks required to link the various scales to the HACR. References to such plans were made in several papers and division reports, but no master document appears to be available.

In the Detector Applications Program, the single-detector-element radiometer used for high-accuracy radiometry has been improved by redesigning the electronics section and using modular construction techniques. The Radiometric Physics Division has several contracts to provide improved radiometers to primary calibration laboratories within the Department of Defense. An improved tunnel trap detector has been developed and is now being assembled for testing. Trap detectors constructed with silicon photodiodes are used as high-accuracy transfer detectors and are calibrated with the HACR at fixed laser wavelengths. The improved trap detectors use six photodiodes arranged to transmit radiation through the tunnel trap detector. This arrangement virtually eliminates reflectance and allows for easier alignment. Trap detectors will be characterized and then used to realize the spectral response and spectral irradiance scale.

Precise knowledge of aperture areas will play a role of ever-increasing importance within radiometry. Progress in these measurements within the Aperture Measurement Program has been swift. The dual approach developed for manufacturing smooth edges and of measuring contours of edges promises to lead to unique world-class standards.

The candela, an SI base unit, has now been realized by the Photometry Program via a group of eight photometers constructed by using glass filters and V lambda-corrected silicon photodiodes. (Correction is necessary to realize the candela, a unit of measure of the apparent brightness of a light source as observed by the human eye.) The photometers are calibrated for absolute spectral response by using working standards directly traceable to the NIST HACR. Implementation of this methodology has resulted in a measurement uncertainty of 0.4 percent for the candela, a factor-of-2 improvement over the traditional method of scale realization. The recently developed tunnel trap detectors

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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are being adapted to further improve the accuracy of the realization of the candela. The goal of 0.1 percent or better for the candela measurement uncertainty is believed to be attainable in the next few years. The technology used to develop the V lambda-corrected silicon photodiodes is now being transferred to U.S. industry and the Department of Defense.

The Photometry Program staff has been working on improvements for all photometric quantities. Recently, a technique has been developed for the absolute measurement of luminous flux and spectral flux using an integrating sphere. Glass standards (opal glass) for the luminance scale will be available in the near future, and luminance flux calibrations are realized through incandescent sources. Also, illuminance and luminance meter measurements are being offered on a routine basis. Further improvements in luminous flux and spectral flux can be expected once the large integrating sphere has been included in the calibration process.

The Detector Metrology Group has been very active in disseminating its knowledge to a number of U.S. industrial companies over the past few years. It has provided support for developing prototype spectroradiometers and radiometers for deep UV measurements, remote sensing instrumentation for sensing of missile plumes, ultrahigh-sensitivity radiometers for photographic applications, new types of silicon photodiode trap detectors, and a new type of UV arc lamp. A great deal of additional knowledge has been amassed that should be shared with the optical radiation measurement community in the United States.

Division-wide Issues

Nonbase, or external, funding constitutes close to 70 percent of the total funding for the Radiometric Physics Division, and the percentage is increasing. The uncertainty of such funding puts not only the division's personnel but also the nation's standards and measurement services in jeopardy.

Many scientifically exciting programs are under way or are being planned in the Radiometric Physics Division, with emphasis on continuing research on the optical properties of materials and microelectronics. The division plans research on novel sensors such as sapphire substrates that would generate new technology in colorimetry, wide-angle apertures such as flat panel screens, and highly absorbent materials, and on radiometry in lasers, crystals, detectors, and sources. Increased awareness of the environment will result in increased emphasis on issues relevant to precision UV measurements: ozone-level monitoring, ocean studies, and similar applications. Other candidates for research are parametric down conversion, precision aperture characterization, and superconducting radiometers at liquid nitrogen temperature. These ambitious and challenging topics are worthy of interest inside and outside of NIST.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Many of the ISO Guide 25 quality requirements are available in the laboratory in one form or another. The division chief has already established a working team to handle ISO requirements and to educate department personnel on ISO standards and requirements. That should bear fruit in a short time.

The division sponsors many first-class papers, seminars, and talks by its staff each year. The feasibility of sponsoring more workshops, classes, and dissemination of electronic videotapes and databases should be explored. Workshops could be of several days' length in order to introduce relevant background information and to convey the results of hands-on experience in the laboratories. The division should offer at least one workshop per year for a particular topic, such as pyrometry or infrared measurements. Additionally, hard copies of presentations should be distributed as working materials during the workshop, traceability should be explained in detail, and the data analysis, including associated uncertainties and formalism, should be discussed thoroughly.

The panel endorses the division's initiative, Advanced Optical Technology, as included in the 1995 budget proposal, and the division's push for research on materials and surfaces. This latter research would underpin nanotechnology, a technology being pursued by major organizations all over the world. The Physics Laboratory's 1993 Competence Building Program proposals, “Fabrication and Characterization of Nanostructures” and “Optical Properties of Novel Materials,” are excellent complementary studies.

Quantum Metrology Division

The Quantum Metrology Division conducts a wide range of activities with a small number (eight) of select permanent staff, a similar number of guest scientists, and collaborators at several external facilities. The division is engaged in high-quality measurement research and sustains a unique body of experimental knowledge and expertise in x-ray metrology.

Synchrotron Radiation Group

The Synchrotron Radiation Group has a rich variety of phenomena under study at the X24A beamline of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The group has the personnel essential for exploration of “discovery-phase” atomic photoexcitation phenomena, several of which they have already observed for the first time. Excitation and decay channels across the argon-potassium edge involving various combinations of photon polarization, electron spectra, and so on are being mapped out in pioneering studies on the NSLS X24A beamline. In addition, the

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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group maintains the beamline for an active user community in surface physics.

The x-ray energy range of the X24A beamline is a major challenge to monochrometer technology. Multilayer mirrors provide a promising solution to the problem of radiation heating. Unlike the known natural crystals with large two-dimensional spacings, multilayer structures of tungsten and carbon can withstand substantial heat loads without irreversible radiation damage. This group has made important progress toward producing multilayers of about 0.4-Å roughness by an innovative process of in situ argon-ion etching during simultaneous carbon-atom deposition. Further development of this method could yield a new class of multilayer mirrors.

The staff of the Synchrotron Radiation Group and the Precision X-Rays and Gamma-Rays Group, in collaboration with the staff from the Ionizing Radiation Division, devised a practical means for voltage measurement and calibration in x-ray tubes used for mammography. Relatively hard x-rays (20 to 50 keV) are used in these medical applications. A prototype device was built and work performed that resulted in a paper and a patent application. This work is an example of the benefit of maintaining a core competence in x-ray physics.

Precision X-Rays and Gamma-Rays Group

The GAM-4 instrument at Institut Laue-Langevin, Grenoble, France, a joint project with NIST, has produced the world's highest-resolution gamma-ray spectra and provided new access to the study of nuclear recoil during the emission of high-energy gamma rays, through the Doppler-broadened line profile.

New high-accuracy measurements of x-ray wavelengths in the actinide elements suggest a systematic discrepancy with theory, an important finding that must be resolved.

The group continues to supply unique ground support for satellite astronomy, exemplified by the observation in March 1993 of a new supernova with the ASTRO-D telescope. Preparation also continues for wavelength measurements of x-rays from heavy ions (e.g., study of helium-like calcium at the Argonne National Laboratory's linear accelerator facility, and study of hydrogen-like dysprosium, lead, and uranium at Gesellschaft für Schwerionenforschung, Darmstadt, Germany).

The program in high-precision x-ray and gamma-ray wavelength measurement and absolute calibration, and their transfer into the optical wavelength scale, continues to yield important data. The x-ray-optical interferometer and the delta-d apparatus were discussed in the panel's fiscal year 1992 report.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Ionizing Radiation Division

The assessments that follow are made in the context of the Ionizing Radiation Division's well-defined strategic plan as documented in February 1992 and presented to the panel at its May 1993 meeting.

Radiation Interactions and Dosimetry Group

Programs of the Radiation Interactions and Dosimetry Group respond to the needs of the radiation processing industry and the need for medical diagnosis and treatment. The group develops dosimetry techniques and standards and provides measurement assurance services and calibration services in support of these industries. The “Technical Activities ” booklet prepared by the group leader and dated December 1992 provides a particularly useful, concise summary of the group's activities.

The group does sophisticated research, much of which (65 percent) is responsive to outside support, and it develops new research areas based on modest core funding. The group's leadership in the development of new dosimetry techniques for both medical and industrial applications has continued since the panel's fiscal year 1992 assessment, and has ranged from the clinical applications of electron paramagnetic resonance (alanine) dosimetry to the development of high-dose measurement techniques for the protection of superconducting magnets. The timely installation of the new Gammacell 220 60Co Irradiation Facility, completed in fiscal year 1992, will support the growing needs of the nation's rapidly developing radiation processing industry. A collateral development is the installation of the 32-MeV Sagittairc linear accelerator in the group's medical and industrial irradiation facility (MIRF). This installation should be a useful addition for both research and technological development and standards development and will provide necessary support for medical and industrial electron dosimetry, in particular for the rapidly increasing number of industrial and academic 10-MeV facilities for both medical product sterilization and consumer product processing. Although the projections for its operation appear optimistic, planning for its application and potential users is well in hand. Radiation processing is an important feature in NIST's 1995 proposed budget initiative for advanced manufacturing.

Consolidation of the operation and maintenance of the three electron accelerators (0.5 to 4.0 MeV), two x-ray sources (300 and 420 keV), two positive ion accelerators (0.1 and 3 MeV), and the flash x-ray facility (2 MeV) has progressed. These facilities, including the electron paramagnetic resonance spectrometers, the 60Co irradiator, and the MIRF linac, have undergone initial refurbishment since the panel's fiscal year 1992 assessment.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Staff of the Ionizing Radiation Division collaborated with staff of the Quantum Metrology Division in a rapid response to the concerns of the Conference of Radiation Control Program Directors about improving the control of mammography installations across the nation. A conference on kilovoltage measurements for mammography was held at NIST to consider continuing radiological safety needs related to diagnostic radiology with x-rays. In addition, the group's participation in the National Cancer Institute's radiation research program in proton dosimetry, the U.S. Nuclear Regulatory Commission's workshop on high-dose-rate sources for cancer therapy, the workshop on National Voluntary Laboratory Accreditation Program (NVLAP) ionizing radiation personnel dosimetry traceability, and the 10th International Conference on Solid State Dosimetry indicates this group's vigorous involvement with customers. The group's morale and industrial participation were much improved over that found by the panel in its fiscal year 1992 assessment.

Office of Radiation Measurement

The mission of the Office of Radiation Measurements (ORM), which has three full-time professional employees, is primarily outreach. The office disseminates standards and techniques required for reliable measurement of ionizing radiation to government, industrial, medical, and defense communities. It is responsible for the national system of secondary standards laboratories for improving the accuracy of field measurements (Measurement Quality Assurance, or MQA), a most successful national measurement assurance program. The office interacts well with the broad spectrum of communities served. Future support by this office of the Department of Energy's program for facility cleanup will be critical. This office's response to feedback from professional societies and trade associations is an important part of NIST's support of U.S. industry. ORM's current goals are to complete the measurement assurance program for the federal laboratories, develop an accreditation system for commercial suppliers of certified radionuclides, and establish MQA for worker protection during nuclear facility cleanup.

The ORM is understaffed, considering the office's increasing activities. The national priorities involving civilian radiation protection and radioactivity site cleanup call for a realistic reconsideration of ORM's role and resources. There was little evidence that ORM had developed long-range priorities.

Radioactivity Group

The Radioactivity Group continues to develop and maintain U.S. standards, confirm these standards internationally, and provide techniques for compatible measurements. The group leader retired in October 1992. A senior scientist is needed to lead

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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these standards programs, which serve large segments (nuclear power, industrial radiation processing and radiography, and nuclear medicine) of U.S. industry. Timely responses are needed for national standards and data for radionuclides with new applications, especially in nuclear medicine. As the panel pointed out in the fiscal year 1992 report, this group's resources are subcritical for fulfilling the group's responsibilities under NIST's congressional mandate and, in particular, the group's broad responsibilities for providing traditional standards for U.S. industry and public health and safety. Deliberate support of the group's programs now would preclude costly duplication of the group's capacity by other agencies in pursuing cleanup programs for radioactive sites.

Neutron Interactions and Dosimetry Group

The Neutron Interactions and Dosimetry Group (1) maintains primary national neutron radiation standards, (2) develops neutron measurement techniques, (3) develops improved dosimetry techniques, (4) provides neutron radiation calibration and measurement technique services to industry, universities, and other government agencies, and (5) carries out basic neutron-related research in support of the above missions.

The work of this group is done mainly at the NIST research reactor in Gaithersburg, Maryland. Collaborative research is also carried out at the Oak Ridge Electron Linear Accelerator, the University of Missouri Research Reactor, and the University of Michigan's reactor (Ford Nuclear Reactor, or FNR).

Over the past several years, the group's Fast Neutron Research Program has established the Materials Dosimetry Reference Facility at the FNR. This effort is in direct support of the materials neutron dosimetry needs of the nuclear power industry and the needs of the metallurgical community engaged in the study of radiation damage in steel structures such as reactor pressure vessels. This facility, which is still in its early stages of operation, will provide fast neutron fluences an order of magnitude greater than those currently available at NIST's research reactor. Two different spectra are available to investigate detector response characteristics and to validate dosimetry measurements. The importance and usefulness of this facility will be discussed by the panel in its fiscal year 1994 assessment.

Other fast-neutron-related programs involve neutron transport through iron shells, a fast neutron calibration spectrometer of interest to the Defense Nuclear Agency, and calculations related to correction factors for fast neutron measuring instruments due to neutron reflections from the walls, floor, and ceiling surrounding the instrument. Calibration work on detection of fast neutron radiation is difficult, important (especially at research reactors and neutron spallation sources), and appropriate for NIST to pursue.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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A new experiment aimed at detecting a correlation between the direction of the spin angular momentum of a decaying neutron and the momentum of the decay particles (proton and electron) was begun, and its feasibility was demonstrated, by the Weak Interaction Physics Program at the national Cold Neutron Research Facility (CNRF) since the panel's fiscal year 1992 assessment. Such a correlation would require a violation of a fundamental principle of physics known as time-reversal symmetry.

Also since the fiscal year 1992 assessment, a reconstructed neutron lifetime apparatus was installed at the end position of the CNRF beam guide NG6. All of the major components of the apparatus have now been debugged and tested. Its aim is measurement of the neutron lifetime to a precision of 0.1 percent. An accurate value for the neutron lifetime is necessary to create a unified theory for the strong, weak, and electromagnetic interactions of nature. The panel will review this long-term experiment in more detail in its fiscal year 1994 assessment.

Of all the experimental techniques available for studying the structure and dynamics of materials and their surfaces, the scattering of thermal neutrons is perhaps the most versatile and powerful. To take full advantage of this technique, methods for polarizing the incident beam and analyzing the polarization of the scattered beam are often necessary. This technique is particularly important for studying magnetic, superconducting, and hydrogen-containing materials. The Laser Polarization of Neutrons Program takes advantage of the high flux of neutrons from NIST's research reactor and NIST's high level of laser expertise to polarize the nuclei of 3He gas by optical pumping. This program polarizes the 3He gas by spin exchange; i.e., anoptically polarized rubidium vapor sample polarizes the dense 3He gas by collisions. Spin-up neutrons (with respect to the 3He nuclear spin) suffer little absorption, whereas spin-down neutrons experience a large neutron absorption cross section in the 3He gas cell. Thus the transmitted beam will be highly polarized (a polarization of the order of 80 percent is possible). The 3He gas cannot be polarized directly with a laser because of the unavailability of tunable ultraviolet lasers.

There are other excellent ways to polarize monoenergetic beams of neutrons, such as by Bragg reflection from magnetic crystals and by mirror reflection by magnetic multilayers, but these techniques are not useful for a broad energy band of incident neutrons. They also require a substantial change in the geometry of the spectrometer in switching from unpolarized to polarized neutrons. A polarized 3He gas cell can be placed in an unpolarized neutron beam, allowing only spin-up neutrons to pass through it, thus providing a polarized beam without change of spectrometer geometry. For time-of-flight neutron spectroscopy at the new pulsed spallation neutron sources, the incident beam has a broad (Maxwellian) energy spectrum. The polarized 3He cell is well suited for such beams.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Funding is assured for 5 years. The goal is to develop prototype devices for use in neutron scattering research at the new spallation sources and at the Advanced Neutron Source scheduled to become operational at the Oak Ridge National Laboratory in the early part of the next century.

This program, along with the Weak Interaction Physics Program and the neutron interferometry research, represents some of the most fundamental physics research under way within the Physics Laboratory.

Division-wide Issues

The Physics Laboratory Annual Report 1992 that was provided for reference during the fiscal year 1993 annual assessment documented steps taken by the Physics Laboratory, and involving the Ionizing Radiation Division, toward stronger interlaboratory collaboration. Examples are the Physics Laboratory's collaboration with the Chemical Science and Technology Laboratory in (1) developing a joint proposal for a 1994 NIST budget initiative on physical and chemical measurements, and (2) sponsoring the Conference on Metrology for Environmental Management on April 14 and 15, 1993. Other documents that were helpful during the program review and in arriving at the following comments were “Physics Laboratory Highlights, 1992,” an informal summary paper on the technical activities of the Radiation Interactions and Dosimetry Group, and the Ionizing Radiation Division's 1992 strategic plan.

Although the Council on Ionizing Radiation Measurements and Standards was set up in 1992, it has yet to assist the Ionizing Radiation Division in program planning and priority setting. More workshops like the Ionizing Radiation Division's March 1992 “National Voluntary Laboratory Accreditation Program (NVLAP) Personnel Dosimetry Workshop” are recommended to stimulate industrial input for planning and priority setting.

The panel found a much-improved morale in the Ionizing Radiation Division staff, which is no doubt partly attributable to the expected increase in support and staff over the next 4 years. This division provides unique and essential support to a U.S. industry that has $50 billion in annual billings. The division's role will increase in importance as the magnitude of U.S. radiological health and safety issues continues to increase.

Time and Frequency Division

The Time and Frequency Division (1) develops and operates standards of time and frequency and coordinates them with other world standards, (2) provides time and frequency services for U.S. clientele, and (3) performs basic and applied research in support of future standards, in ways to disseminate services, and in measurement methods.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×

The division has a full-time staff of 40, and it hosted 20 long-term guest researchers and 5 postdoctoral associates in fiscal year 1993. The division collaborates with 18 industrial companies. The division 's research is unquestionably first-rate. The morale is strong, and there is a pride of achievement and a sense of common mission among the staff.

The division is reviewed here according to major programs rather than according to groups.

New Cesium Frequency Standard; NIST-7 Program

During fiscal year 1992, NIST-7, an optically pumped cesium-beam atomic clock, became operational and was put “on the air.” It is designed ultimately to operate at an uncertainty level of 1 × 10-14. It is already performing at an uncertainty level of 4 × 10-14. NIST-7 is the most accurate optically pumped primary frequency standard in the world. Previous cesium clocks have been based on magnetic state selection and detection. The fundamental advantage of this new standard clock is its greatly enhanced signal-to-noise performance, which allows for more rapid evaluation of its accuracy.

Time Dissemination and Transfer Program

The time scale stability will be improved to hold to Coordinated Universal Time (UTC) to within 100 nanoseconds. The resources and talent necessary to realize this goal are available within the division. Input from NIST will help the International Bureau of Weights and Measures to reduce the time lag between receipt of data and issuance of time differences from UTC. This improvement in stability will benefit the telecommunications industry. The Time and Frequency Division has an excellent record of dissemination and transfer of time standards, as evidenced by the following:

  1. The Automated Computer Time Service operated by the division has experienced substantial growth since its inception in 1988, with a doubling of its activity in a period of well under 1 year. The current level of use is more than 4,000 calls per day.

  2. The division operates two radio stations (WWV and WWVB) in Fort Collins, Colorado, and in Hawaii (WWVH) that provide time and frequency broadcasts. It also provides a time code broadcast from the GOES weather satellite operated by NOAA. It is a credit to the division that WWVH stayed on the air and survived the damage from Hurricane Iniki in September 1992.

  3. A two-way satellite time transfer is being implemented using a NIST-developed time transfer modem that could become the world standard.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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  1. The Global Positioning System common view technique will be continued and improved by enhancing the NIST-designed receiver to measure the ionosphere delay.

  2. Work on time jitter or phase stability has substantially helped the telecommunications industry. The division has developed secondary standards that can be transported from laboratory to laboratory and into industry. This is a previously neglected area of work that supports the division and the outside world. The high level of outside funding is proof that this effort has been beneficial.

Diode Lasers Program

The panel pointed out in its fiscal year 1992 report that diode laser technology development was vital to the development of the next generation of optically pumped atomic and ionic frequency standards. Funds from the NIST director's Competence Building Program were used to hire another professional staff member for the development of diode lasers. Present development involves a number of collaborations within NIST and with industry; however, the work would benefit from better technical coordination throughout NIST. There are many applications for tunable diode lasers of high stability, e.g., in laser manipulation of atoms on surfaces in nanostructures, optical pumping for frequency standards,a transferable standard for length, and in spectroscopy for chemical analysis, analysis of pollutants, and similar applications.

Development of high-stability tunable diode lasers is an important new technological development at NIST based on cooperation with U.S. high-technology industry.

New Initiative in Cryogenic Oscillators (Proposed)

Because of the extraordinarily narrow frequency discrimination capability that has resulted from development of trapped ion capabilities, it is appropriate for NIST to develop oscillators to serve as “frequency-maintaining flywheels” to provide signals to be steered by the discriminators. Although new crystal oscillator developments can still offer improvements, these devices are limited by their mechanical nature and are sensitive to vibration. It is well known that low-temperature operation offers considerable advantages for realizing highly stable oscillators. These advantages include reduced levels of additive white thermal noise, very small loss tangents in dielectric materials such as sapphire, improved mechanical and thermal characteristics, superconductivity, and superfluidity. The panel notes that NIST's growing emphasis on creating generic technologies provides an opportunity to promote low-temperature device development within the Time and Frequency Division.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×
Assignment for Development of Length Standard

Because length is now derived from the unit of time, the second, through the defined velocity of light, the Time and Frequency Division has the expertise but only a secondary responsibility for developing the standard of length. The primary responsibility for a standard of length resides with the Precision Engineering Division of the Manufacturing Engineering Laboratory. The Time and Frequency Division, with its laser expertise, could be assigned responsibility for developing and implementing a unified time-length standard. The essential aspect of this standard would be a laser-generated light source at a frequency directly related to the NIST primary frequency standard. Development of techniques for determining distance standards based on the laser-generated light source should not necessarily be the responsibility of the Time and Frequency Division.

Opportunities in Nationwide Initiatives in Computers and Information (Panel Comments)

Time synchronization in telecommunications is an increasingly important factor in schemes to link computers across the country, across the oceans, and in space. Such challenges in the development of a “national information highway” are more formidable than originally thought. There are opportunities, and perhaps responsibilities, for the Time and Frequency Division to assist in the rapidly emerging telecommunications industry in the synchronization of signals.

Fundamental Basic Physics Research (a Panel Comment)

The research within the Time and Frequency Division is extremely well structured to support the time and frequency standards mission of the division; however, it also stands on its own as high-quality fundamental physics research. An example of the division's fundamental research is the recent experiment in which π-polarized light scattered from two trapped atoms was shown to give rise to “Young's-like” two-slit interference fringes, while σ-polarized light did not. This experiment, carried out by the division's Ion Storage Group, has ramifications for the study of the fundamental nature of quantum mechanical phenomena.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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PANEL RECOMMENDATIONS--FISCAL YEAR 1993
Laboratory-wide Recommendations
  • The panel recommends that the Physics Laboratory extend the “Advanced Algorithms, Software, and Applications” proposal to include the development of on-line visualization and a state-of-the-art physics computational center to support the database effort. This extension could have a major impact on NIST's general responsibilities to provide to industry such scientific and technical data as plasma radiation data and atomic energy level data.

  • The panel recommends more interlaboratory proposals such as the joint evaluation of reference data (with the Chemical Science and Technology Laboratory) for coordinating NIST's support of U.S. industry.

  • The panel recommends that the advanced optical technology initiative be pursued as a high-priority program, not only because it supports the mission of NIST and will strengthen NIST's ability to interface properly with its extramural Advanced Technology Program, but also because NIST is the only place in the United States where the necessary expertise exists in optical measurement and instrumentation techniques to significantly advance optical technology.

  • The panel recommends that the laboratory's name be changed to the Physical Sciences and Technology Laboratory. This name not only would more accurately reflect the laboratory' s activities and responsibilities but also would be more in parallel with the names of other NIST laboratories.

Division-level Recommendations
Electron and Optical Physics Division
  • The panel recommends additional emphasis on making the toroidal gradient monochromator operational.

  • As new synchrotron radiation facilities come on-line, the panel recommends that managers of the Synchrotron Ultraviolet Radiation Facility (SURF) project elucidate the advantages that make SURF a unique measurement tool. In particular, future plans for SURF should capitalize on the unique advantages of the optical quality of SURF's radiation.

  • The panel recommends that long-range planning be undertaken for the Electron Physics Group.

  • The panel recommends that x-ray fluorescence measurements using existing instruments be focused on problems that do not require the high brilliance of the Advanced Light Source.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Atomic Physics Division
  • The panel recommends that the Atomic Radiation Data Group secure the assistance of a computer scientist with expertise in database software for the efficient implementation of its database efforts.

  • The panel recommends that final assembly and testing of the electron beam ion trap (EBIT) be accelerated.

  • Because the Gaseous Electronics Conference (GEC) reference reactor program has direct applications to the U.S. semiconductor industry, the panel recommends additional support for the program.

Molecular Physics Division
  • The panel recommends that the Molecular Theory Group play an active role in and fully support the Physics Laboratory's effort to be part of the federal High Performance Computing and Communications (HPCC) initiative.

Radiometric Physics Division
  • Because the ambient background infrared (ABIR) facility has several challenges to meet, the panel recommends that the Radiometric Physics Division prepare a detailed time line to track the various facets of the planned improvements.

  • The panel recommends that (1) a well-thought-out plan and time line be developed for the optical Properties of Materials Program on the basis of customer input, (2) two additional full-time professionals be hired and adequate Scientific and Technical Research and Services (STRS) funding be secured for this program, and (3) a high priority be placed on implementing International Organization for Standardization (ISO) Guide 25 policies.

  • The panel recommends that the Radiometric Physics Division examine all of the scales to be integrated with the high-accuracy cryogenic radiometer (HACR) and prepare a master plan to address the tasks required to achieve this objective, associated funding required, and the proposed time line for completion.

  • Several papers and presentations have been prepared since the fiscal year 1992 assessment; however, the panel recommends that dissemination of the technologies being developed within HACR be intensified.

  • Work on measurement aperture areas should continue to be given high priority by the Radiometric Physics Division.

  • The Detector Metrology Group should emphasize technology transfer, e.g., by conducting periodic workshops or seminars.

  • The Radiometric Physics Division should emphasize updating SP 250 publications and developing an official manual for laboratory personnel on International Organization for

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Standardization (ISO) quality requirements as defined in ISO Guide 25. In addition, seminars should be organized for the benefit of personnel that would bring in representatives from outside organizations who are familiar with the standardization process and with the quality requirements.

  • The panel recommends that the Radiometric Physics Division develop long-term (10- to 15-year) goals and document plans.

  • The Radiometric Physics Division should increase its emphasis on dissemination of information regarding optical calibration techniques and measurement techniques and the dissemination of routine measurement techniques.

Quantum Metrology Division
  • The Quantum Metrology Division should expand into a broad-based x-ray technology effort, following the example of the mammography tubes project.

Ionizing Radiation Division
  • The Committee on Interagency Radiation Research and Policy Coordination should help develop priorities for the Office of Radiation Measurement 's services.

  • In its fiscal year 1992 assessment the panel recommended that a senior scientist be sought to lead standards activities in the Radioactivity Group. It reiterates that recommendation here.

  • The panel recommends that the strategic plan for the Ionizing Radiation Division be updated annually.

  • The panel recommends an integration of the Office of Radiation Measurement and the Radioactivity Group in view of their overlapping missions. The identities of the two groups could be preserved under a new “radiation standards group.”

  • The panel recommends that the Council on Ionizing Radiation Measurements and Standards interact with relevant trade organizations to provide feedback for the Ionizing Radiation Division's planning.

  • In view of the Ionizing Radiation Division chief's plan to retire in June 1994, the panel recommends that a nationwide search begin immediately to recruit a senior scientist of international reputation as a replacement.

Time and Frequency Division
  • The panel recommends that the Time and Frequency Division invest in the personnel and equipment necessary to develop precommercial cryogenic oscillators.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
×
  • The panel recommends that NIST formalize, in some useful way, a new definition of the meter in terms of the velocity of light.

Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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Suggested Citation:"7 PHYSICS LABORATORY." National Research Council. 1994. An Assessment of the National Institute of Standards and Technology Programs: Fiscal Year 1993. Washington, DC: The National Academies Press. doi: 10.17226/9192.
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