Ionizing Radiation Division

DESCRIPTION OF THE DIVISION

The mission of the Ionizing Radiation Division is to develop, maintain, and disseminate the national standards for ionizing radiation and radioactivity in order to meet the needs related to health care and the environment and those of academia, U.S. industry, and homeland security, and to conduct underlying basic research in these areas. The division maintains the national measurement standards for the Système International (SI) derived units for radiation dosimetry (the gray) and activity (the becquerel). This division is composed of three groups—Radiation Interactions and Dosimetry, Radioactivity, and Neutron Interactions and Dosimetry.

Radiation Interactions and Dosimetry Group

The mission of the Radiation Interactions and Dosimetry Group is to advance the accurate and significant measurement of dosimetric quantities important in the radiological sciences through programs in the dosimetry of x-rays, gamma rays, electrons, and other charged particles.

The projects in the group are classified in five areas: theoretical dosimetry, quantum metrology, medical dosimetry, homeland security applications, industrial applications, and protection and accident dosimetry. A special focus on homeland security continued in FY 2007. Experimental and calculational support was provided for the performance standards and the testing and evaluation protocols developed for explosives and nuclear detection used for homeland security. This work included participation in several working groups writing American National Standards Institute (ANSI) standards. Significant progress, including the following, was made in a number of the group’s measurement standards and calibration services:

  • Progress in developing a unique type of signal analysis related to water calorimetry;

  • Reference dosimetry calibrations for photon-emitting 125I, 103Pd, and 141Cs radioactive seeds used for prostrate cancer treatment;

  • The use of the group’s clinical electron accelerator to develop a second-generation water calorimeter to serve as a standard for accelerator-produced high-energy x-ray beams used in cancer treatment;

  • The completion of the software for the first Internet-based e-certification service for radiation processing dosimetry; and

  • Prototype testing of equipment for detecting radiation sources in cargo containers.

The overall staffing level of the group is acceptable for accomplishing current projects. Several members of the staff are approaching retirement age, but a succession plan is in place. The group relies on guest researchers, students, and contractors to do a significant portion of the work. This use of outside personnel seems to be acceptable, but



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Ionizing Radiation Division DESCRIPTION OF THE DIVISION The mission of the Ionizing Radiation Division is to develop, maintain, and disseminate the national standards for ionizing radiation and radioactivity in order to meet the needs related to health care and the environment and those of academia, U.S. industry, and homeland security, and to conduct underlying basic research in these areas. The division maintains the national measurement standards for the Système International (SI) derived units for radiation dosimetry (the gray) and activity (the becquerel). This division is composed of three groups—Radiation Interactions and Dosimetry, Radioactivity, and Neutron Interactions and Dosimetry. Radiation Interactions and Dosimetry Group The mission of the Radiation Interactions and Dosimetry Group is to advance the accurate and significant measurement of dosimetric quantities important in the radiological sciences through programs in the dosimetry of x-rays, gamma rays, electrons, and other charged particles. The projects in the group are classified in five areas: theoretical dosimetry, quantum metrology, medical dosimetry, homeland security applications, industrial applications, and protection and accident dosimetry. A special focus on homeland security continued in FY 2007. Experimental and calculational support was provided for the performance standards and the testing and evaluation protocols developed for explosives and nuclear detection used for homeland security. This work included participation in several working groups writing American National Standards Institute (ANSI) standards. Significant progress, including the following, was made in a number of the group’s measurement standards and calibration services: • Progress in developing a unique type of signal analysis related to water calorimetry; Reference dosimetry calibrations for photon-emitting 125I, 103Pd, and 141Cs • radioactive seeds used for prostrate cancer treatment; • The use of the group’s clinical electron accelerator to develop a second- generation water calorimeter to serve as a standard for accelerator-produced high-energy x-ray beams used in cancer treatment; • The completion of the software for the first Internet-based e-certification service for radiation processing dosimetry; and • Prototype testing of equipment for detecting radiation sources in cargo containers. The overall staffing level of the group is acceptable for accomplishing current projects. Several members of the staff are approaching retirement age, but a succession plan is in place. The group relies on guest researchers, students, and contractors to do a significant portion of the work. This use of outside personnel seems to be acceptable, but 26

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there is a concern if funding for these outside employees decreases. Most of the major equipment used by the group is old and in need of replacement. A serious problem arises from the fact that newer equipment would have to be housed in heavily radiation shielded bunkers, whereas the group is housed in an older building whose shielded facilities do not meet current needs. This is a major issue which may require that a new building be constructed. Radioactivity Group The mission of the Radioactivity Group is to develop new technologies for the accurate measurement of radioactivity for various applications. This mission includes the development of standards for research, for the determination of very low levels of radioactivity, and for biological medical applications. The group develops methodology for all the applications given in the mission statement and the application of these techniques to service projects in which the NIST staff coordinate with the scientific community. The range of projects is very broad and includes the development of accurate counting techniques (an automated ion chamber, an anti-coincident system, a gamma spectroscopy system, and various low-level counting techniques). Cutting-edge techniques for radionuclide metrology are being developed and applied to the quantification of standard reference materials. A final area is in the field of nuclear medicine. In this rapidly expanding field, various applications particularly applied to positron emission tomography (PET) and positron emission tomography/computed tomography (PET/CT) are being developed. A significant fraction of the effort of this group is working with outside users in a service mode. In several areas, extra staffing is required because several key scientists are approaching retirement age. Extra staffing is needed particularly in the nuclear medicine area. In order for the Radioactivity Group to work at the forefront of the various areas, leading-edge equipment, including a PET/CT facility, should be available. Future research might be done using an animal scanner, although justifications and protocols should be reviewed and approved by the appropriate committees before the acquisition of such a system is initiated. Neutron Interactions and Dosimetry Group The mission of the Neutron Interactions and Dosimetry Group includes both fundamental research and service activities. The research is anchored in precision measurements with neutrons of fundamental physical constants and data that address issues such as the neutron lifetime, the strength of underlying weak couplings, and tests of symmetry violation such as parity and time reversal. The applications range from neutron tomography and imaging to neutron calibrations. The balance between fundamental research and service activities is approximately equal. While the research makes use of a variety of NIST instruments, the key facility used is the seven neutron beam lines that the group operates at the NIST Center for Neutron Research (NCNR) 27

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reactor, which is a leading center for neutron research in the United States. It is a successful users’ facility, drawing researchers from commerce, universities, industry, and various national laboratories. The fundamental science program includes some very challenging projects with high potential payoffs. Examples include the following: • Measurements of the neutron lifetime and beta decay correlations that, in the context of the standard model, will determine the strengths of the vector and axial-vector coupling constants. These measurements also place important bounds on beyond-the-standard model interactions. One of the group’s lifetime measurements employed ultracold neutrons confined by a three- dimensional magnetic trap. • Measurements of the spin precession of polarized cold neutrons passing through 4He, an effect arising from parity violation associated with the hadronic weak interaction. (The parity violation allows one to separate tiny weak effects from the dominant strong interaction.) This experiment is important to a 30-year effort to understand the isospin structure of the weak interaction between nucleons. • Measurements of fundamental properties on the neutron, including the neutron charge radius and the n-3He scattering length. The neutron charge radius measurement exploits an interferometer developed by the group, an instrument important to both fundamental research and service activities. The neutron, while electrically neutral, has nonzero charge radius, through which it can interact electromagnetically with charged particles. This interaction in turn produces a phase shift as a neutron beam passes through a silicon crystal, near the Bragg angle. Such a measurement would complement nuclear physics measurements made at flagship nuclear physics facilities such as the Thomas Jefferson National Accelerator Facility. The n-3He measurements are possible because of dramatic improvements in the lifetime of cells containing highly polarized 3He—a major technical achievement by the group. Some of the important applications include the following: • The construction of the advanced Neutron Imaging Facility and its use in probing the performance of hydrogen fuel cells. This method of radiographic imaging of the water production and movement within the fuel cell, not possible previously, is very effective because of the large neutron capture cross section on protons in the water. The neutron imaging program has achieved unprecedented resolution and provided unique and invaluable data to industry. • The development of techniques for high-efficiency neutron detection in liquid scintillator. The long-term goal is inexpensive, fast-neutron detection that can operate in real time to identify fissile material in cargo or other shipping containers. The group is also involved with the development of performance standards from neutron detectors designed for homeland security applications. • The calibration of neutron sources for clients such as DOE laboratories. The 28

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workhorse facility for this calibration is a manganese sulfate bath system that uses a long-lived (and therefore stable) calibration source to normalize measurements. • The development of more precise tools for measuring neutron fluxes. Two methods under development are based on (n,α) on boron, in which a gamma ray from the final 7Li nucleus is also detected; and on detecting repeated Lyman α transitions produced as the recoil ion, generated in 3He(n,p)3H, passes through the gas. These tools will, in turn, help the group to improve its neutron lifetime and other fundamental measurements. The Neutron Interactions and Dosimetry Group has just nine staff members and is thus remarkably lean, given the variety of fundamental and service work being done and its task of maintaining and operating seven beam lines. The group’s successes derive in part from the successful collaborations established with external users. Two of the group’s beam lines are now operated as a user facility, with an informal external advisory/review committee providing advice on priorities and scheduling. A major upgrade of the reactor facility will take place between now and 2010, providing the group with four new beam lines. This development is potentially of great significance: with modern focusing, it is expected that the flux available in fundamental experiments could increase by a factor of 10, making the NIST facility comparable to the world’s best, Grenoble’s Institut Laue-Langevin. While this is a very positive step forward, it will also require the group to shoulder major new responsibilities. It will be important to increase the level of staffing in the group substantially, both to exploit new capabilities and to manage the heavier load of users that would be expected. There appears to be no funding currently in place to instrument the new beam lines, although apparently some may become available. It is important that the Physics Laboratory address this need. The group has some outside support (from NSF and DOE), but the levels are low. It is not clear whether to expect success in increasing the level of outside support: the Spallation Neutron Source (SNS), a major new DOE facility for pulsed neutrons, has begun operations at the Oak Ridge National Laboratory. For many applications, NIST, with its continuous flux, will remain the best facility. However, DOE users might be expected to focus their research at the DOE facility. The Physics Laboratory should explore interagency agreements that would provide neutron experimenters with the broadest choice of facilities while lowering barriers to interagency funding and cooperation. This is scientifically sensible: some experiments developed at NIST may, as second-generation efforts, migrate to the SNS. ASSESSMENT OF THE DIVISION The following is a partial list of recently completed and ongoing major projects of the Ionizing Radiation Division: • Dosimetric support for a local company developing a malaria vaccine, • The establishment of a dose assurance program for the irradiation of mangos in India, 29

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• X-ray spectral measurements, • High-energy computed tomography (CT) for homeland security, • Neutron tomography and imaging, • Wide-angle polarization analysis, • Therapeutic alpha emitters, • Radionuclidic metrology, • Quantitative imaging, and • The development of a transportable, personal PET phantom for patients. Examples of the significant accomplishments of this division include the following: • Substantial progress has been made in the development of high-energy CT as a result of a collaboration with the Savannah River National Laboratory; • The first observation was made of the irradiative decay mode of the neutron; and • The NIST triple-to-double coincidence ratio spectrometer has been rebuilt and improved. The Ionizing Radiation Division is actively participating in a new NIST initiative in biomedical imaging; $380,000 of new funding has been allocated to the division for this purpose. Collaborative projects related to PET and PET/CT have been initiated with other NIST divisions and laboratories and a university. With respect to resources, the division is currently staffed with 52 permanent NIST employees and a number of postdoctoral fellows, guest researchers, and summer undergraduate research fellowship students, bringing the total staff number to 98. Funding for FY 2007 was approximately $10 million, with over 50 percent coming from the Department of Homeland Security (DHS) and other outside organizations. This high dependence of funding on one outside customer is of concern. The quality and direction of the projects in the Ionizing Radiation Division are in line with expectations for superior returns on the investment being made. There are issues with respect to facilities and funding. The issues with respect to facilities include the condition of the physical plant that houses the Radiation Interactions and Dosimetry Group and the Radioactivity Group and the need for modernizing or replacing much of the radiation-producing equipment used by the division. Extension of the Experimental Hall coupled with the development of new beam lines at the NCNR will result in the Neutron Interactions and Dosimetry Group’s obtaining four new beam lines. It is essential that funding for the experimental equipment and staff needed to use these new beam lines efficiently be made available. Technical Merit Relative to State of the Art The Ionizing Radiation Division’s programs are, overall, as good as or better than those in other national and international standards laboratories. Examples include brachytherapy seed and mammography equipment calibrations and fundamental neutron 30

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research. Adequacy of Infrastructure The division’s aging Building 245 needs a major upgrade or replacement; in particular, new radiation-shielded facilities are required to house new accelerator equipment, high-dose-rate brachytherapy calibrations, and a medical imaging facility. Some equipment needs upgrading or replacement, including the instrumentation for a new neutron beam line, the aging accelerator and a need for spare parts, and the new nuclear imaging equipment. Funding is adequate but very heavily dependent on the Department of Homeland Security. Several retirements are expected in the next few years in the division, but succession planning is in place. The work of the division relies heavily on postdoctoral fellows and students. Achievement of Objectives and Impact The projects being carried out support the division’s mission. The division works collaboratively with other divisions in the Physics Laboratory, with other NIST laboratory divisions, and with numerous other organizations. The technology development and scientific research are at a very high level of technical merit. The objectives of the Ionizing Radiation Division are to develop, maintain, and disseminate the national standards for ionizing radiation and radioactivity in order to meet the needs related to health care and the environment, and those of academia, industry, and homeland security, and to conduct underlying basic research in these areas. The Ionizing Radiation Division develops dosimetric standards based on the SI unit gray; develops neutron standards; develops and provides standards for radioactivity based on the SI unit, the becquerel; and works through strategic alliances, external funding (largely from the DHS), and links with other national and international metrology institutions. CONCLUSIONS The vast majority of the projects in the Ionizing Radiation Division are well thought out and relevant to the mission of the division and to the needs of those who use the calibrations, standards, and research results produced. There are three major areas of concern: the heavy dependence of the division on DHS funding, the condition of the physical plant that houses the Radiation Interactions and Dosimetry Group and the Radioactivity Group, and the need for modernizing and replacing much of the radiation- producing equipment used by the division. The extension of the Experimental Hall coupled with the development of new beam lines at the NCNR will result in the Neutron Interactions and Dosimetry Group’s obtaining four new beam lines. It is essential that funding be made available for the experimental equipment, its operation, and staff needed to use these new beam lines efficiently. The overall quality of the Radioactivity Group’s work is among the best in its field. Major input on potential projects comes from the Council on Ionizing Radiation 31

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Measurements and Standards, which generates a list of recommended projects; however, CIRMS does not prioritize the items on that list. An external advisory committee should be appointed to help the Radioactivity Group select and prioritize both new research projects and the specific areas of service collaboration. Funding for a major renovation to the existing building or, preferably, a new building, should be established for the Ionizing Radiation Division. Shielded radiation cells should be constructed to house the needed modern radiation equipment and high- dose-rate calibration equipment required for industrial-scale dosimetry and medical imaging and calibrations. Careful attention should be given to the current sources of funding for the division. The heavy dependence on DHS funds may lead to a future problem when this funding goes away. An external advisory committee should be established to assist in prioritizing research and service-related projects. Staff and funding in the Neutron Interactions and Dosimetry Group should be increased to allow the efficient use of the new facilities at the NCNR, and staffing in the Radioactivity Group should be increased to meet the growing needs in medical imaging and nuclear medicine. 32