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3. CURRENT STATUS OF NEU'1KON-SCATTERING FACILITIES IN 1~E UNI'lbu STATES In this chapter we describe briefly the existing neutron- scattering facilities at the five National Laboratory neutron university reactor facilities. We sources and two major also provide a summary of the trends in users and publications In Chapter 4 we associated with U.S. neutron facilities. provide a comparison with facility development and user trends at foreign laboratories.] It is clear from these data that there has been a striking increase in users and change in user patterns over the past decade along with - 1A variety of sources of information were used by the Panel in assembling summaries of users, publications, instrumentation, and total neutron-scattering budgets. These included the earlier National Academy of Sciences and Department of Energy reports cited in the Introduction, the Annual and special reports of the DOE and its National Laboratories, the National Bore au of Standards, and the University of Missouri, along with those of the Ins titut Laue-Langevin at Grenoble and other neutron-scattering centers in Europe. The Panel went further, however, to assure up- to-date suitably coordinated information and statistics by individually contacting the major neutron centers in the United States, Western Europe, Japan, and Canada concerning users, publications, and other information relevant to the comparisons made in the report. It should be noted that the Panel did not attempt to provide similar comparisons with neutron-scattering facilities in the Soviet Union, Eastern Europe, India, or other neutron efforts worldwide. A summary of these facilities can be found in the earlier NAS and DOE reports mentioned above. 6

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7 qualitatively new research opportunities in a variety of fields. It should be noted that in general U.S. neutron sources also serve a wide variety of scientific and programmatic needs that are unrelated to neutron-scattering research. At present, about half of the total operating costs of major neutron sources (about 613.5 million) are associated with neutron scattering, while the remainder is related to other highly important and diverse national needs, including isotope production, chemical trace analysis, radiation damage, nuclear physics, ultracold neutron research and radiation standards. This multiple program use of neutron sources in the United States is beneficial, since it can provide broad-based support and cost-effective operation. Bowever, it can sometimes create serious difficulties if one of the programs loses or withdraws support, thus threatening the stability or schedule of source operation. The major neutron sources in the United States used for scattering research are briefly described in the following summaries. The research reactors in general operate 24 hours a day in a quasi-continuous schedule with brief shutdowns for maintenance and refueling. The pulsed-source schedules are currently more curtailed, as noted in the summaries. FACILITY DESCRIPTIONS High Flux Beam Reactor (EFBR)--Broothaven National Laboratory The High Flux Beam Reactor is a 60-MW reactor using enriched fuel and D2O as a moderator and primary coolant. The core

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8 is small (48-cm diameter), resulting in a thermal neutron density that is peaked outside of the core, where beam tubes tangential to the core provide neutron beams with low fast- neutron contamination. The thermal flus isl x1015 neutrons/cm2- sec at the 8-cm-diameter thermal beam-tube tips. To provide intense beams of low-energy neutrons, a liquid H2 moderator has been installed in one beam tube that is equipped with a small-angle scattering diffractometer and a high-resolution three-axis spectrometer. Situated on the seven remaining tangential beam tubes are four conventional three-axis spectrometers that are used mostly for inelastic scattering studies and powder diffraction, a three-axis spectrometer and two diffractometers equipped with four-circle goniometers for single-crystal and protein diffraction studies, as well as two additional diffractometers used mainly for small- angle scattering. Four diffractometers have position-sensitive detectors. One of the three-axis spectrometers is often devoted to polarized neutron studies. Under a cooperative development are a new polarized-beam crystal spectrometer with a spin-echo capability (with Japanese scientists) and a medinm-resolution macromolecule diffractometer (with Exxon Research Laboratories). including conventional Additional ancillary equipment, and 3Be cryostats and high-pressure sample environments are routinely available. Staff scientists carry out independent research programs in addition to assisting external users, who make collaborative arrangements largely through direct contact with interested staff scientists. A more formal user policy including peer review will be implemented in the near future.

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9 Intense Pulsed Neutron Source (IPNS)--Argonne National Laboratory The Argonne Palsed Neutron Source produces bursts of neutrons with a peak thermal flux of ~4 ~ 1014 neutrons/cm2-sec at a repetition rate of 30 Hz and is at present the most intense pulsed source in the world. Neutrons at the IPNS are produced by a 450-500 MeV proton-beam incident on a depleted uranium target at an average current of ~12 pA. A polyethylene moderator surrounds the target to reduce the energy of the neutrons to allow neutron-scattering research. Twelve horizontal and two vertical beam holes surround the moderator assembly. A cold moderator (80~) is available for three of the beams. A separate uranium target is used for fast-neutron irradiation and arranged so that the samples can be irradiated at liquid helium temperature. IPNS currently operates 6 months a year. The radiation effects facility receives the beam 25 percent of the time, and the neutron-scattering target 75 percent of the time. There are seven instruments currently available in the user mode, including two high-resolution powder diffractometers; a single-crystal diffractometer operating on the Lane principle with a position-sensitive detector of the scintillation type; a small-angle diffractometer, also with a position-sensitive detector; a crystal-analyzer spectrometer primarily for observing H-modes in chemical systems; and two chopper spectrometers with incident energies ranging from 50 to 1000 MeV, which allow scattering measurements over a broad range of energy and wave-vector transfer. These neutron-scattering instruments are scheduled in the "user" mode, i.e., allocation of 75 percent time is made

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10 by a Program Committee, which reviews proposals twice a year. Three additional instruments are under development: a polarized neutron instrument for studying refraction from surfaces; a diffractometer built to search for ordered nuclear moment arrangements in 3Be below 1 my; and a spectrometer for spectroscopy in the electron volt range. Accelerator modifications and installation of an enriched uranium target are planned over the next 2 years to increase significantly the intensity of IPNS. Massachusetts Institute of Technology Reactor (MITR) The MITR is a 5-MOO, heavy-water moderated reactor whose core and beam arrangement was modernized in the 1970s to provide beam tubes with accessible fluxes approaching 1014 neutrons/cm2-sec. There are currently three two-axis spectrometers in use, one with temperature stability control for neutron interferometer studies and two for general-purpose diffraction with changeable monochromators and wavelengths. The MITR is also utilized for a variety of other research and applications in nuclear engineering, trace analysis, radiation effects, and isotope production. National Bureau of Standards Reactor (NBSR) The NBSR is a heavy-water moderated research reactor currently operated at 10 M' and awaiting final Nuclear Regulatory Commission approval to double the power to 20 ME, which will provide a flux at the beamrtube entrances of 2 ~ 1014 neutrons/cm2-sec. The NBSR has eleven radial beams (15- cm diameter), nine of which are currently dedicated to neutron-

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11 scattering research. The reactor geometry combines a split- core fuel arrangement and large vertical divergence (~100 min) to provide high-intensity, low-background beams at the sample position for scattering applications. The facilities available for diffraction include a multiple-detector high- resolution powder diffractometer; a four-circle single-crystal diffractometer; a biological crystallography station (NBS- NIH) using a position-sensitive detector; a small-angle- scattering spectrometer that features a focusing collimating O system, tunable wavelength (4.5-12 A), and a large t65 cm s 65 cm) position-sensitive detector that can be rotated around the sample. Instruments for inelastic scattering include three variable-incident energy triple-asisspectrometers, one of which is equipped with a high-intensity beryllium filter analyzer for chemical spectroscopy, and a multidetector time-of-flight crystal-chopper spectrometer with variable incident energy. A polarized-beam spectrometer is also under development. Scattering experiments are possible between 0.3 and 1800 ~ and at magnetic fields up to 7 T. All neutron-scattering instruments are scheduled each month by a committee of major users from the National Bureau of Standards, other federal laboratories, and universities. External requests for facility use can be addressed to committee members or to the neutron group leader. Funding has recently been provided for installation of a large (25-cm-long, 36-cm-diameter) cold-neutron source in the reactor core, which will serve a variety of instruments for cold-neutron research on materials. Sixteen other facilities at the NBSR serve research and applications in chemical trace analysis, radiation standards, nuclear physics, and isotope production.

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12 Oak Ridge National Laboratory Reactors (ORNL) The High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory operates at a power level of 100 ME. Light water serves as coolant and moderator in the annular fuel region. Target rods for production of transuranium isotopes are located in a central flux-trap region. There are four horizontal beam tubes of 10-cm inner diameter with an average flux of 1 ~ 1015 at their tips. These beams deliver neutrons to nine scattering instruments: two variable incident energy (Eo) triple-axis spectrometers; a fixed ED triple-axis unit; a polarized-beam triple-axis spectrometer; an ultrasonically pulsed time-of-flight instrument; a liquid diffractometer; a four-circle, single-crystal diffractometer; a double perfect- crystal small-angle scattering (SANS) instrument; and a 30-m SANS facility with an area detector. The last instrument was constructed with NSF funds and is operated by the National Center for Small-Angle Scattering Research. A new high- intensity two-axis diffractometer with a curved position- sensitive detector is being developed with Japanese support with a potential for real-time crystallographic studies. The Oak Ridge Research Reactor (ORR) operates at 30 ME with light water as coolant and moderator and beryllium as reflector. The primary purpose of this reactor is for materials-irradiation experiments, but there are six horizontal beam tubes of 17-cm diameter for scattering experiments. The thermal flux near the beam-tube entrances is about 2 1014 neutrons/cm2-sec. The Ames Laboratory operates three instruments at the ORB: a variable-E triple-axis diffractometer, a polarized-beam diffractometer, and a two-axis diffractometer.

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13 In addition, ORNL operates a 5-m SAN S instrument with an area detector and a two-axis diffractometer. Proposals for the NSF-supported SAN S facility are reviewed by a special committee and scheduled as they are received; there is normally a three- to four-month waiting period. Other ORNL instruments are available to users either by informal arrangements or by written proposals that are reviewed by Oak Ridge staff members. University of Missouri Research Reactor (MURR) MURR is a 10-MW pressurized-water, beryllium-reflected flux- trap reactor located in Columbia, Missouri. There are six beam ports with four used for neutron-scattering research. The flux available at the source end of the beam ports is 1014 neutrons~cm2-sec. There are currently seven neutron- scattering instruments: two four-circle single-crystal diffractometers; one triple-axis spectrometer; two powder diffractometers--one with a position-sensitive detector, the other with a five-detector system; a fized-wavelength o (4.7A)small-angle scattering facility that uses amultidetector and has 4.5-m flight paths before and after the sample; and a double-crystal monochromator-interferometer instrument. Facilities are open to outside users by informal arrangements with neutron-scattering staff members at HERR. The reactor has a number of other major facilities used for gamma-ray scattering (diffraction, quasi-elastic scattering, and Compton scattering), neutron activation analysis, radio-pharmaceutical and transmutation-doped silicon production, radiation-effects studies, neutron radiography, and key neutron beams for tomography and cross-section work.

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14 An improved triple-axis spectrometer and another diffractometer are expected to be built during the next 2 years, and an engineering study has been funded for a possible doubling of the reactor power. Weapons Neutron Research/Proton Storage Ring Facility (WNR/PSR) Los Alamo s National Laboratory The WNR/PSR being developed at the Los Alamo s National Laboratory is a pulsed spallation neutron source for neutron-scattering research in condensed-matter physics, chemistry, materials science, biology, and polymers. It is an interdisciplinary facility that is shared with nuclear- and neutrino-physics research. A beam of 800-MeV protons is provided by the Los Alamo s Meson Physics Facility (LAMPF). At present, the WNR can utilize only about 0.5% (~5 pA) of the LAMPF beam. However, the PSR will permit by 1986 the use of 100 pA of LAMPF protons with a much reduced pulse width of 0.27 psec. At that time, the peak thermal neutron flux in the pulse is expected to be 1016 neutrons/cm2-sec at 12 Hz, making WNR/PSR directly competitive in neutron intensity with the new British pulsed source (SNS) at the Rutherford Laboratory. At present six beam lines are available for condensed- matter research, three each for elastic and inelastic scattering studies. Two of these instruments, a filter difference spectrometer for vibrational spectroscopy and a single-crystal diffractometer, are operated in a user mode, while the remaining instruments are under development. A general-purpose powder diffractometer is expected to become a user instrument in 1984. A program advisory committee (shared with ANL) currently

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15 meets twice a year to decide on proposals for beam time. The total time available for neutron-scattering studies currently is 60 percent of the LAMPF operating schedule (6 months/year in 1982-1983) and will increase to 80 percent in 1986. A total of ten neutron-scattering instruments is planned for completion by the end of 1986. Summary of Facilities Other neutron-diffraction facilities also exist at smaller university reactors for student training and research, most notably several instruments at the University of Rhode Island. In Table 1 we summarize the neutron-scattering instruments currently available at major U.S. neutron sources. The table shows that there are a total of 53 instruments (compared, e.g., with 114 instruments currently operating and over 40 under development in Western Europe). The relative effectiveness of these facilities is, of course, closely related to intensity, energy and momentum range, and flexibility, for example, factors that are impossible to reflect in a single table. Ingeneral, currentneutron-scattering capabilities in the United States are clearly still competitive internationally in the areas of triple-axis spectrometry with resolutions >0.2 meV, single-crystal and powder diffraction for both steady-state and pulsed sources, polarized-beam research, high-resolution biological diffraction, and neutron interferometry. In a later section, critical neutron instrumentation and measurement capabilities currently unavailable or not fully competitive in the United States will be summarized.

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16 TABLE 1 Snamary of Nentron- Scat taring Instruments Avail able in the United States A. RESEARCH REACTORS 1. Diffractometers BNL MIT NBS ORNL MURR 2 2. Spectrometers Inter Three- ferometer SAN S Axis 2~ 5C BNL MIT 1 NBS ORNL - 3 H~ 1 1 1 Two-Axis Two- (Multisector Four- Axis or PSD) Circle Four- Circle (PS0) 2 1b 1 2a 1 1b 1 2 Time-of- Polarized Flight Beam - 1 4c 4 1 2 B. PULSED NEUTRON SOURCES 1. Diffractometers (Elastic) Single Powder Crvstal SANS Beam ANL 2a 1 1 LASL 1 1 2. Time-of-Flight Spectrometers ANL LASL - Chopper Crystal Filter Analyzer Analyzer Analvzer 2 1 1 . . aDedicated high-resolution powder diffractometers. bThese instruments configured primarily for biological structure research. COne of these three-axis instruments is sometimes used for polarized beam studies. dPrimarily for structure of liquids and glasses.

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17 It should also be noted that aside from the facilities described above, there are ongoing state-of-the-art efforts at the various neutron centers in the development of area detectors, multilayer focusing and polarizing monochromators, focusing collimators, neutron interferometers and choppers, all of which are important for the development of advanced instrumentation for reactor or pulsed sources. While in some cases U.S. laboratories have been pioneers in such advances, our efforts in general have a low-to-modest level of support and manpower compared with instrumentation development projects in Europe (some of which are described below). As a result, the implementation of new classes of instruments based on these developments has been generally much slower in the United States. THE USER COMMUNITY The U.S. neutron-scattering user community has changed considerably since the 1977 report of the National Research Council (Neutron Research on Condensed Matter, National Academy of Sciences, Washington, D.C., 1977), both in the number of users and in the kinds of science being done. A summary of the total number of users per year at O.S. neutron-scattering facilities during the past 6 years is given in Figure 1. For the purposes of this report a "user,' has been defined as a scientist who directly participated in a neutron-scattering experiment at least once during a given year. A scientist who visited a given neutron center more than once to perform experiments is counted only once.

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18 500 400 300 200 100 o Users / 0~ - - ~/ /Publ ications D 1977 1 978 1979 1980 YEAR 1981 1982 1983 FIGURE 1 IJ. S. neutron-scattering research--users and publ ications .

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19 No attempt has been made to identify scientists who might have used more than one neutron source. Also shown in Figure 1 are the number of publications in the 1977-1983 period. The user trends in Figure 1 show that the number of U.S. users of neutron-scattering facilities has more than doubled during the past 6 years and has gone up 80 percent between 1980 and 1983. This rapid increase in the total user community is broadly reflected in the individual numbers for the majority of the neutron research centers. Major factors include the installation of new or improved small- angle scattering facilities at the research reactors, the commissioning of the Intense Pulsed Neutron Source at Argonne National Laboratory, and other reactor instrumentation developments including high-resolution diffraction and improved polarized-beam and triple-axis spectrometers. It should be noted that this large increase occurred in spite of the shutdown of the CP-5 reactor at Argonne during 1978-1979. It is clear from the user trends that, as has occurred in Europe, the introduction of new or improved neutron instruments that provide new measurement capabilities greatly increases the utilization of such neutron facilities by the scientific community. The expanded neutron-scattering community shown in Figure 1 also reflects a significant change in the distribution of users from the various scientific disciplines and in some cases the introduction of almost entirely new user groups (e.g., polymer science). In broad terms, the neutron user community in 1983 is distributed as follows: condensed- matter physics, 35 percent; chemistry, 23 percent; materials science, 16 percent; polymer science, 13 percent; biology, 13 percent. Thus while condensed-matter physics has shown

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20 a healthy increase over the past 6 years (-33 percent), these users now represent a considerably smaller percentage of the total community than in 1977 (~45 percent). Other user groups, most notably in polymer and materials science and biology, have shown much greater relative increases (~150 percent), stimulated largely by the availability of new state-of-the-art SAN S and high-resolution diffraction facilities. The chemistry community has also grown at approximately twice the rate of the condensed-matter physics community. Since the number of full-time scientists at the major neutron centers has increased very little during the past few years, these numbers represent a decided increase in part-time users of neutron-scattering facilities. In fact, this has put a great strain on the scientific and technical staff at the National Laboratories in seeking to serve the increasing user community while continuing to meet the program needs of their own agencies. Currently the approximate distribution of users is as follows: federal laboratories and agencies, 30 percent; universities, 60 percent; and industry, 10 percent. The breadth of the current neutron-scattering community is reflected in the diversity of the organizations that participate in research at the various neutron centers. A list of universities, industries, and laboratories doing independent or cooperative neutron research during this past year is given in Appendix A. One notable trend in the user distribution is the considerable increase over the past 6 years in the number of students using neutron- scattering facilities either full time or part time in their research. Between July 1982 and June 1983, there were 92

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21 student users at the various neutron centers. This number is both significant and encouraging since the education and participation of young scientists in modern neutron- scattering science is essential for the future health and vitality of the field. It should be noted here that, while the majority of users utilize the federal laboratory facilities (almost 90 percent in 1983), the university facilities have trained or provided facilities for close to 30 percent of the student users. Another measure of the productivity and vitality of the neutron-research community is, or course, the number of publications resulting from the use of neutron-scattering facilities. The publication numbers assembled from the various neutron centers for the past 6 years are shown in Figure 1. It can be seen that a large increase in neutron- scattering publications has occurred that roughly parallels the rapid increase in the user community. Thus we observe an increase of slightly more than 60 percent over this period, almost all during the past 3 years. This increase is smaller than the overall percentage increase in users. This lag is to be expected for new users (in many cases using new facilities) in any field. In fact an even greater lag in publications was noted during the rapid expansion of users at the Institut Laue-Langevin (ILL) in Grenoble during the 1970s. In addition it should be noted that part-time users of any major facility will rarely be as productive in publication as the core of full-time users (who represented a much larger fraction of the total neutron user community in the mid- 1970s). As will be seen below, the current number of publications per user compares quite favorably with comparable figures for the ILL and other European facilities.

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22 It is also interesting to note that a combination of the facility numbers in Table 1 with the user figures in Figure 1 gives about 10 users/instrument. This is rather close to the comparable ratios assumed for synchrotron facilities in the Report of the Subcommittee on U.S. Synchrotron Radiation Facilities (Current Status of Facilities Dedicated to the Production of Svnchrotron Radiation, National Academy Press, Washington, D.C., 1983). COMPARISON WITH TEE EUROPEAN COMMUNITY We now present a brief review of foreign neutron-scattering users and facilities, concentrating on Western Europe, where the major expansion has occurred during the past 12 years. Western Europe has over the last decade developed a user community more than double the size of that in the United States, driven by a major investment (most notably at the ILL) in new classes of instrumentation and a highly organized, well-funded user policy. A summary of users and publications over the past 6 years is given in Figure 2. In developing the user numbers we have applied the same criteria as we outlined above for the United States, but there is a greater uncertainty in the n user" figures for non-ILL facilities owing to the greater chance of "double counting" scientists who use both ILL and their own neutron facilities. It should be noted that while the total European user community tripled during the 1970s, the period shown in Figure 2 shows a less dramatic rise, reflecting the saturation of facilities at ILL and elsewhere. A notable feature of these current-user

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1 ,300 1 ,200 1,100 1 ,000 900 _ _ 800 cr: m 700 5 ~ 600 o 500 400 300 200 100 o _ ~ _ / P' / . _ ,: 23 _ - Total User ILL Users Total Publications _ ~C1 . _ I LL Publication 1977 1978 1979 1980 YEAR 1 981 1982 1 983 FIGllRE 2 Summary of users and publications from Western Europe .

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24 numbers is the dominant position of ILL, which accounts for about half of the users and publications in Western Europe. In fact, the figures show that the ILL alone has about 25 percent more "users" than the total for the United States. The current number of neutron-scattering instruments at the ILL is 26, and the total annual budget (including a program to fund the expenses of users from France, Germany, and Great Britain) is about 625 million (roughly the same as the entire O.S. effort in neutron-scattering research). Taking into account the rapid development and planning of new instruments (~50) in Western Europe, a user community exceeding 1500 would be expected by about 1987. Beam time on the ILL is scheduled almost entirely in the "user" mode through the review of formal proposals by panels assembled to represent various disciplines and kinds of instruments. In addition, every neutron facility has instrument-responsible scientists and technicians associated with it who are assigned to assist outside scientists in using the facilities. While the average number of users per instrument per year in this mode (about 20) is considerably higher than in the United States, the number for the United States (10) is somewhat higher than the average of the other European facilities. Publication rates per user are roughly the same for the United States as for Western Europe. By comparison, figures for neutron-scattering publications in Canada, which has maintained a traditional role in this field, show an average rate of about 40 publications in recent years. The Japanese, who are engaged in a vigorous expansion in both reactor-based and pulsed neutron research, now show a publication rate approaching 100 papers per year. While these comparisons attest to the continuing productivity

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25 of the U.S. neutron centers, the O.S. ability to serve the needs of the user community is limited by the lack of incremental resources for scientists and technicians to provide direct user support at the major neutron centers. Another key problem facing the U.S. neutron facilities in seeking to maintain an internationally competitive position in this field is the lack of resources for the development of new classes of instrumentation (leading to new science). A major advantage of the ILL and other European centers over the past decade has been the flexibility and funding to develop such new instruments and the cold neutron sources, guide tubes, and focusing monochromators, for example, needed for their development. In the next chapter we will briefly review the impact of this relative lag in U.S. capabilities.