ACCELERATORS LINEAR ELECTRON ACCELERATOR. Linac beam handling system. ELECTRON VAN DE GRAAFF ACCELERATOR, 4 MeV This accelerator, based on the principle of the Van de Graaff electrostatic generator, produces both continuous and pulsed beams of electrons with good energy resolution and continuous control of beam current and energy. Its capabilities make possible a wide variety of experiments using electrons or photons. Capability: ENERGY: continuously variable 0.8 to 4.0 MeV. OUTPUT CURRENT: 10-9 to 10-3 ampere dc. PULSE LENGTH: 1 microsecond. Applications: Interactions of electrons and photons with matter; dosimetry measurements; isomer activation; electron channeling in solids; bremsstrahlung production studies; characteristic radiation production; nuclear activation; photofission experiments; radiation simulation measurements; radiation damage and failure studies. Availability: Beam time is available to NBS staff, other agency and university users, industrial users, and guest workers. Operation only by qualified X-Ray Physics Section staff, under Dr. Charles E. Dick. Literature: NBS Technical News Bulletin, August 1962, Vol. 46, No. 8, pages 107-110. Contact: Dr. C. E. Dick, Applied Radiation Division, Radiation Physics Building, Room C216, Phone 301921-2201. LINEAR ELECTRON The linear accelerator (linac) facility was designed for maximum flexibility, beam quality, and beam handling to satisfy the needs of a large variety of programs. It is a high-intensity source of electron, photon, and neutron beams with excellent stability and definition. Capability: ENERGY: continuously variable 10 to 150 MeV. POWER: 60 kilowatts, average. CURRENT: 0.6 milliamperes, average. 3.5 amperes, peak (short pulse operation). REPETITION RATE: variable to 720 pps. PULSE LENGTH: 0.001 to 5 microseconds. ENERGY SPREAD: from linac, 2 percent full width at half maximum; from beam handling system, 0.04 percent full width at half maxi mum. EXPERIMENTAL ROOMS: four, with personnel access to one while beam is directed into another. An on-line data handling system is available, and data reduction programs are available. Applications: Neutron total cross section measurements by time of flight (above-ground facility); neutron fission yields; neutron flux standards; neutron capture cross sections; fast neutron activation analysis; electron and photon dosimentry; pulsed radiolysis of biochemical systems; electron scattering; electrodisintegration of light nuclei; photonuclear physics with monoenergetic and polarized photons; photon activation analysis; dosimetry and dose distribution using radiochromic dyes; electron and photon beam measurement standards; production of radioactive sources. Availability: Beam time is available to NBS staff, other agency and university users, industrial users, and guest workers. Operation only by qualified Linac Operations Section staff under J. E. Rose. Literature: NBS Technical News Bulletin, August 1962, Vol. 46, No. 8, pages 107-110. Scientific Research, June 1966, Vol. 1, No. 6, pages 24-26. Contact: Dr. C. D. Bowman, Chief of Nuclear Sciences POSITIVE-ION The positive-ion 3 MeV Van de Graaff facility at the National Bureau of Standards has been designed primarily for experiments involving keV and MeV energy neutrons. It includes a HVEC model KN-3000 Van de Graaff accelerator and two target rooms. The accelerator is capable of operation in dc mode as well as in a variety of pulsed beam modes. Momentum analyzed beams can be supplied to any of six ports in a low scattering environment or to a single port in a heavily shielded room. Protons and deuterons are the ion species routinely accelerated. Capability: Values listed are routinely available. Extended capabilities may be developed for special applications. ENERGY: 0.8 to 3.0 MeV. BEAM INTENSITY: 1 to 200μA. Analyzed Beam: ENERGY: protons-0.8 to 3.0 MeV; deuterons— BEAM INTENSITY: 0.3 to 20.9μА. ENERGY REPRODUCIBILITY: 5.0 keV. Rf PULSING: 1.0 and 3.3 MHz repetition rates An on-line data handling capability based on a Applications: Standard neutron cross section measurements, neutron flux standards, neutron experiments involving time of flight, neutron capture cross section measurement, fast neutron activation analysis, neutron dosimetry, radiation damage studies, charged particle studies. Availability: Accelerator time is available to NBS staff and outside users to the extent that the work does not conflict with the neutron standards program. The use of a member of the Van de Graaff staff is recommended for operation of the machine and set-up. Contact: Dr. A. D. Carlson, Neutron Standards Section, Radiation Physics Building, Room B119, Phone 301-921-2677.. SYNCHROTRON ULTRAVIOLET RADIATION Synchrotron radiation in the far ultraviolet is highly collimated, nearly linearly polarized, and of calculable intensity. It is well-suited for studies in atomic, molecular, biomolecular and solid-state physics, chemistry, engineering and medicine. Capability: The NBS Synchrotron Ultraviolet Radiation Facility (SURF) has been converted into a storage ring. Beam currents of 2 mA have been accelerated and two beam lines are operative. The third beam line should be available in 1976. With a microtron injector the storage ring is expected to accelerate a 40 mA beam to a maximum energy of 260 MeV. The expected intensity in the region 600 A to 1200 Ă is 3 X 1011 photons per second per milliradian of orbit for an instrumental resolution of A/λ = 0.001. Instrumentation planned and existing includes: 11 c) Two 2000 Å—60 Å monochromators (toroidal grating), resolution 0.5 Å to 1.0 Å. d) 925 Å 40 Å 2.2-m grazing incidence monochromator, resolution to 0.1 Å, with 10-10 torr vacuum chamber, photoelectron analyzer, and manipulators. e) Medium temperature heat-pipe ovens, 0.3m and 1.0m, to 1100 C. One oven of the rotating type handles materials that wet a wick with difficulty. f) Calibrated detectors, 2000 Å - 200 Å. g) Two spectrometer calibration lines with a direct view of the beam. Applications: The enlarged SURF will be used for atomic and molecular absorption spectroscopy, optical properties of materials, electron density of states in solids, surface studies (including angular distribution of photoelectrons as a function of angle of incidence and polarization vector), radiation damage studies in substances (including those of biological origin), calibration studies, precision photoabsorption cross-section measurements in solids and vapors, and photoelectron spectroscopy of gases. Availability: To any qualified research worker from NBS or other Federal agencies. Contact: Dr. Robert P. Madden, Chief, Far UV Physics Section, Physics Building, Room A251, Phone 301921-2031. ACOUSTIC FACILITIES Literature: J. Acoust. Soc. Amer., Vol. 52, No. 4 (Part 1), Oct. 1972, pp. 1071-1076. Contact: Dr. E. Magrab, Sound Bldg., Room B106, Phone 301-921-3607. This facility consists of a sound and vibration-isolated room whose inner surfaces are lined with 1.78-meter long glass-wool wedges and whose free-field dimensions are about 10 X 6.7 X 6.7 meters. Access to the room is by means of a steel wire mesh floor supported by concealed I-beams. Instrument hangers, each capable of supporting about 100 kilograms, are mounted on all six surfaces of the room. The space is lighted, air conditioned and provided with electrical outlets and conduits for communications cables. Capability: The room provides good free-field sound conditions from about 50 Hz to at least 63 kHz. Upper bounds for wide-band ambient noise are about 30 dB re 20 μN/m2 for C-weighting and 23 dB for Aweighting. (The actual ambient level cannot be measure with a commercial sound level meter since equivalent instrument noise exceeds the ambient acoustic noise.) Applications: Microphone calibration, loudspeaker measurements, sound level meter calibration, noise measurement, psychoacoustic experiments, radiation and scattering experiments, general use when a quiet environment is needed. Availability: When not otherwise in use and when staff members are available to ready the facility for the user. ACOUSTIC The chamber is a vibration-isolated, shell-within-shell type structure of massive reinforced concrete construction with inside dimensions of 9.14 X 7.62 X 6.10 meters. A steel plate, double-leaf entrance door provides a clear opening to the chamber of approximately 2 X 3 meters. The chamber is equipped with a unique set of adjustable, variable-speed, rotating vanes to improve the diffusion of the sound field. The interior of the chamber and the surrounding onemeter-wide air envelope are lighted, air conditioned and humidity-controlled and provided with electrical outlets and conduits for communication lines. Numerous pipe-sleeve openings of various sizes also are available for other specialized uses such as conduits for hydraulic, pneumatic, fuel or exhaust lines. Capability: Although experimental verification has not been completed, the chamber is designed to provide a highly diffuse sound field in the frequency range 100 to 4000 Hz, and to permit reasonably accurate acoustical measurements to be made at frequencies as low as 80 Hz and as high as 10,000 Hz. The wide-band ambient noise level in the chamber with the vanes stationary is about 30 dB re 20 μN/m2 for C-weighting and about 36 dB with vanes rotating at 5 rpm. The reverberation time Teo (60 decibel decay) is approximately 25 seconds at 100 Hz and about 4 seconds at 4000 Hz. 60 Applications: The chamber generally is used for measurement of sound power output of noise and sound sources (e.g., machinery, appliances, loudspeakers, sirens), sound absorption of architectural materials (e.g., acoustical tile, carpeting, drapery), random incidence calibration of sound level meters, microphones and noise exposure meters, and human response to noise. Availability: When not otherwise in use and when staff members are available to prepare the facility for the user. Literature: NBS Tech. News Bul., Vol. 52, No. 12, Dec. 1968. Contact: Dr. I. Pallett, Sound Building, Room A155, Phone 301-921-3381. ANTENNAS NEAR-FIELD SCANNING FACILITY for measurement of gain, pattern, and polarization characteristics of microwave antennas. The panels of pyramidal wedges prevent reflections. ANTENNA MEASUREMENT FACILITIES The Electromagnetic Division of the NBS Boulder Laboratories has recently perfected two new and highly accurate methods for determining antenna characteristics from measurements made at greatly reduced distances. The methods are known as the near field scanning (NFS) and extrapolation techniques and two types of unique facilities have been constructed in order to implement them. 1. Near-Field Scanning Facility Capabilities: This facility is used to measure the nearfield phase and amplitude over a plane area close to the test antenna. From this information it is possible to accurately calculate the gain, pattern, and polarization characteristics at all distances from the antenna, near field as well as far field. The absolute gain can be determined to within about± 0.15 dB, the polarization axial ratio to within about ±0.10 dB/ dB and side lobe levels can be obtained down to -50 or 60 dB. The side lobe accuracy is typically about ±1.0 dB at the -40 dB level. (The exact uncertainties will depend on the frequency, type, and size of antenna, etc.) The new automated system is capable of scanning an area 15 ft X 15 ft square and can be adapted to take data over a cylindrical or spherical surface as well. Applications: Measurement of antenna patterns, gain, and polarization from about 750 MHz to 75 GHz. Any other application where it is necessary to have a detailed knowledge of electromagnetic field configurations, e.g., scattering experiments. Availability: To any qualified NBS research workers, after an initial training period with supervisor. In appropriate instances individual research workers from other Federal organizations and industry can gain access to the facility. Literature: [1] D. M. Kerns, "Correction of Near-Field Antenna Measurements Made with an Arbitrary But Known Measuring Antenna," Electron. Lett., 6, pp. 346-347, May 1970. [2] R .C. Baird, A. C. Newell, P. F. Wacker, and D. M. Kerns, "Recent Experimental Results in Near-Field Antenna Measurements," Electron. Lett., 6, pp. 349-351, May 1970. [3] A. C. Newell, and M. L. Crawford, "Planar Near-Field Measurements on High Performance Array Antennas," Report, National Bureau of Standards NBSIR 74-380, July 1974. 2. Extrapolation Range Facilities Capabilities: The Electromagnetics Division operates two "extrapolation ranges," a 60-meter outdoor range and a 10-meter indoor range, for performing high accuracy measurements of gain and polarization of directive antennas. These ranges each consist of two moveable towers that roll on accurately aligned rails, enabling one to measure the signal transmitted between a pair of antennas as the separation distance between the antennas is varied. Such data are used to determine the desired far-field (infinite separation distance) gain and polarization properties of the antennas. This method is the most accurate method known for evaluating directive antennas. Above 1 GHz, the gain accuracy is typically± 0.08-0.10 dB and polarization axial ratio can be determined within ± 0.05 dB/dB. Such accuracies are normally not achievable on the best far-field antenna ranges and the dimensions of an extrapolation range are only 1/5 to 1/10 as large as a far-field range. Applications: High-accuracy measurements of antenna gain and polarization above about 500 MHz with no discernible upper limit. Other microwave experiments that require the precise motion of a source and/or receiver of electromagnetic energy. Availability: To any qualified NBS research workers, after an initial training period with supervisor. In appropriate instances individual research workers from other Federal organizations and industry can gain access to the facility. Literature: Accurate Measurement of Antenna Gain and Polarization at Reduced Distances by an Extrapolation Technique, A. C. Newell, R. C. Baird, and P. F. Wacker, IEEE Trans. A&P, Vol. AP-21, No. 4, July 1973, pp. 418-431. Contact: Dr. R. C. Baird, Chief of Fields and Antennas Section, Radio Building, Room 4085, NBS Boulder, Colo. 80302, Phone 303-499-1000, ext. 3301. BUILDING RESEARCH FACILITIES ROOFTOP ANTENNA The rooftop antenna test facility is located on the upper flat portion of the roof above Wing 6 of the Radio Building. Capability: This test facility was built to provide a means for measuring antenna reflection and transmission coefficients. Two rigid coaxial rf cables and a multiconductor intercom and power cable connect to the automatic network analyzer in the laboratory below. The automatic network analyzer provides for the rf signal generation and detection requirements. Applications: Complex reflection (impedance) and transmission coefficients of antennas can be measured by making use of the automatic network analyzer over the frequency range of 0.1 to 18 GHz. Antennas can be measured at frequencies below 100 MHz by connecting the lead-in coaxial cables to other rf sources for signal generators and components for signal detection. Although this latter equipment is not presently dedicated for use with the rooftop antenna range it is available for use from projects. Availability: To any qualified NBS research worker, after an initial training period with supervisor. In appropriate instances individual research workers from other Federal organizations can gain access to the facility. Contact: D. H. Russell, Program Chief, Microwave Measurement Services, Radio Building, Room 4633, NBS Boulder, Colo. 80302, Phone 303-499-1000, ext. 3811. ACCELERATED WEATHERING LABORATORIES. Compressed air gun for shooting ice spheres to simulate hail damage to building materials and systems. ACCELERATED WEATHERING LABORATORIES The effects of sunlight, rain, hail, atmospheric contaminants, and salt spray are simulated by accelerated cycling on building materials and systems such as wall coverings and sidings, caulking, roofing, flooring, paints, and plastic coatings. Seven exposure stations throughout the United States and Puerto Rico provide a diversity of natural weathering conditions. Capability: Radiant-energy sources of the accelerated test machines include single and twin carbon arcs, a fluorescent sunlamp/black-light unit, and both water and air-cooled xenon arcs. Monitoring is by dosimeters, radiometers, or actinometers. Some machines have temperature, humidity, and water spray controls, or light/dark cycle controls. A high-humidity chamber is used to subject samples to cycles of water condensation and drying. Flammability of roofing is tested in a small spread-of-flame apparatus. A compressed-air gun fires ice spheres up to 21⁄2 inches diameter against roofing and siding specimens at measured speeds up to 145 feet per second. |