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research into problems involving extensive development of microwave instrumentation. Pioneering efforts in the study of transient and high temperature molecules have led to designs and techniques which affect spectrometer performance in many ways. Operational flexibility and sensitivity have been significantly extended in both the high and low frequency extremes of the traditional microwave region.

Capability: Two separate spectrometer systems are available with klystron sources and requisite hardware to cover the complete range from 2 to 132 GHz. Harmonic generation equipment extends the operation further into the millimetre region. Conventional septum-type waveguide absorption cells, used for studies of static systems, include a 12 ft gold-plated cell (3.3 GHz cutoff), 15 ft brass cell (8 GHz cutoff), and 4 ft all-stainless and Teflon cell for special handling of reactive gases (12 GHz cutoff). All three conventional cells can be cooled to dry ice and the special stainless cell may be heated to 300°C. Several parallel plate cells are available complete with discharge and pyrolysis sample generating apparatus and fast-continuous-flow vacuum systems. Special ovens will allow operating temperatures to 1000°C for certain experiments.

Applications: Analyses of rotational spectra of polar gas-phase molecules yielding structural parameters, electric dipole moments, quadrupole coupling constants and spectroscopic details such as vibrationrotation interactions, etc. Stable molecules with vapor pressures of a few micrometres of Hg at temperatures below 1000°C are readily accessible. A variety of small transient molecules with lifetimes of the order of 10 ms have been successfully studied in the flow systems. Certain laser-microwave double resonance and laser pumped reaction systems are also within the range of capabilities.

Availability: To qualified research workers on a collaborative basis with NBS staff or in special cases where background and experience is adequate on a guest worker basis. It should be emphasized that these spectrometer systems are hand-built, state-ofthe-art devices and require extended experience for competent operation.

Contact: Dr. Donald R. Johnson, Molecular Spectroscopy Section, Physics Building, Room B268, Phone 301-921-2021.

MÖSSBAUER

SPECTROSCOPY OF METALS

and electronic environment of an atom embedded in a solid material. By detecting the conversion ele: trons that emanate from a sample, very thin surface layers can be studied. Differences between the su face and bulk can be observed by also detecting the primary Mössbauer effect gamma rays.

Capability: Solid specimens of irregular shapes w outside dimensions up to 30 cm can be utilized. M mum size is about 0.5 cm diameter and 5μm tha ness. Transmission spectra can be obtained (on pow ders or foils) as a function of temperature in apples magnetic fields up to 50kG. On selected specimen time delayed perturbed angular correlation stude can also be made.

Applications: Measurements of isomer shifts, mat netic hyperfine fields and electric field gradients per mit studies of phase composition, magnetic proper ties, electronic structure and diffusion. Application to corrosion studies, surface effects, and other meta lurgical problems.

Availability: To any qualified NBS research worker In appropriate instances, researchers from other ganizations can gain access to the facility. Scientist from U.S. universities, federal agencies and ind tries, and from abroad have qualified to use th equipment in the past.

Literature:

[1] Nuclear Resonances in Metals: NMR and Mössbauer Effect by I. D. Weisman, L Swartzendruber and L. H. Bennett in Meas urement of Physical Properties, E. Passag and R. F. Bunshah, Editors. (Wiley-Inter science, New York), V. 6(2), 1973. [2] Mössbauer Spectrometer Calibration Us TiFe, Nat. Bur. Stand. (U.S.) Tech. News B 54, No. 10, page 239 (1970).

Contact: Dr. L. H. Bennett, Alloy Physics Sector Materials Building, Room B-150, Phone 301-921-2

MULTICHANNEL

FLAME SPECTROMETER

This flexible system was designed and assembled a NBS to perform precise spectral measurements the emission and atomic absorption modes us flames or similar high temperature "thermostates The spectrometer used to detect the radiations or inating from the excitation source is a conventiona

1-m grating instrument, arranged to focus on a pho

Mössbauer effect utilizes the nuclear properties of or a metal pa

various isotopes to probe the local chemical, magnetic

with eight exit slits.

Capability: Operable as a spectrograph, a scanning monochromator, or multichannel instrument. Measures in emission and atomic absorption modes for one element at a time, or up to 8 chemical species simultaneously. The output is either analog or digital. Applications: Analysis for alkali and earth alkali metals in body fluids, agricultural products, soils, air, te and water samples; for elements from the I to VIII groups in alloys; for trace elements such as Pb, Cd, Hg, Cu, Cr, Ni.

Availability: To any qualified NBS research worker, after an initial training period by R. Mavrodineanu. Literature:

[1] R. Mavrodineanu, Discussion of some ex-
perimental and fundamental flame spectro-
scopy, Revue GAMS, 1971, no. 3, 39-60.
[2] R. Mavrodineanu and H. Boiteux, Flame
Spectroscopy, John Wiley and Sons, 1965,
pp. 721.

Contact: Dr. R. Mavrodineanu, Assistant Chief, Spectrochemical Analysis Section, Chemistry Building, Room B-218, Phone 301-921-2141.

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

The NMR method makes use of the magnetic and electric moments of atomic nuclei to probe the local environment about selected nuclei in materials. Appropriate nuclei of virtually any chemical element can be used, but considerations such as isotopic abundance, sensitivity and atomic motion restrict studies to preselected problems.

Capability: Metallic specimens generally should be in the form of -325 mesh powder, but other forms including single crystals are possible. Wide-line NMR spectroscopy with laboratory electromagnet and high-power pulsed NMR spectroscopy with superconducting magnet. Data acquisition system used for sensitivity enhancement. Ferromagnetic NMR spectroscopy also available. Temperature and pressure variations possible.

Applications: Measurements of Knight shifts, relaxation times, electric quadrupole interactions and lineshapes permit studies of electronic structure, defect structure and diffusion. These have been important primarily in the study of metals, alloys, and intermetallic compounds but occasional attention has been given to practical problems outside of metallurgy such as detecting cancer in live mice utilizing

NMR.

Availability: To any qualified NBS research worker. In appropriate instances, researchers from other organizations can gain access to the facility. Scientists from U.S. universities, federal agencies and industries, and from abroad have qualified to use this equipment in the past.

Literature: Nuclear Resonances in Metals: NMR and Mössbauer Effect by I. D. Weisman, L. J. Swartzendruber and L. H. Bennett in Measurement of Physical Properties, E. Passaglia and R. F. Bunshah, Editors. (Wiley-Interscience, New York, V. 6(2), 1973.

Contact: Dr. Lawrence H. Bennett, Chief of Alloy Physics Section, Materials Building, Room B150, Phone 301-921-2982.

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greatly enhancing the beam intensity. The wavelength of neutrons used in this spectrometer can be varied from 1.5Å to 4.0Å in order to optimize the resolution with the sample attentuation characteristics.

Applications: This spectrometer has applications in
the determination of shape, size and interaction of
macromolecules as well as similar properties of de-
fects in materials, magnetic correlations at extended
distances, and density fluctuations near the critical
point of phase transitions. Neutron small-angle scat-
tering has particular application to submicroscopic
particles of low population densities, where light and
x-ray scattering suffer from absorption and poor res-
olution.

Availability: Instrument time can be scheduled for
appropriate experiments of projects of NBS staff, after
the proposed measurements are reviewed by the
Users Committee for these facilities. Outside users
can also be accommodated depending on the type of
measurements and the available resources.
Literature:

NBS Reactor: Summary of Activities, Oct. 1971-
Sept. 1972, Nat. Bur. Stand. (U.S.) Tech. Note
758 (Mar. 1973).

Contact: Dr. Robert Carter, Chief, Reactor Radiation
Division, Materials Building, Room A106, phone 301-
921-2421.

NUCLEAR IRRADIATION
FACILITIES

Capability: An extensive number of well-characterized irradiation facilities offer a wide range of neutron and/or gamma environments to levels exceeding 1011 neutrons per square centimeter per second. These include five distinct pneumatic facilities, eleven in-core vertical thimbles with inside diameters up to 31⁄2 inches, and seven vertical reflector thimbles with 42 inch openings. These facilities are used simultaneously and can accommodate tens of thousands of samples a year.

Applications: Most common use is in neutron activation analysis for detection of trace elements in parts per million, billion, or trillion. Other uses include preparation of isotopes for tracer work, preparation of isotopes for medicine, production of gamma and positron sources, studies of radiation damage, and the characterization of standard reference materials.

Availability: All facilities are available to qualified scientists. Each sample to be irradiated must be ac

companied by an irradiation proposal form for se review. The packaging of each sample must be proved by the staff of the Reactor Operations Sect.c who can also provide guidance in the preparation: the irradiation proposals.

Literature: W. F. Sheely, The NBS Reactor: Its Descrp tion and a Guide to Its Use by Experimenters, No: Rept. 9081 (1966).

Contact: Tawfik M. Raby, Deputy Chief, Reactor Rà diation Division, Reactor Building, Room A137, Phone 301-921-2523.

TIME-OF-FLIGHT

NEUTRON SPECTROMETERS

This instrumentation utilizes either crystal monochremators or phased-choppers to select monoenerge": neutrons, which are scattered by a sample and de tected 2.5 to 3.8 metres away by multiple neutron detectors at scattering angles between 10° and 105 The energy of the scattered neutrons is determined by time-of-flight analysis.

Capability: The spectrometers provide incident ne tron beams ranging in energy between 3 meV 2 cm-1) and 100 meV (800 cm-1) and cover a spectra range for inelastic scattering of 0.5 meV to 100 me (4 to 800 cm-1). The available resolution varies from 0.2 meV (at the lowest energies) to 5 meV. The range of momentum transfers (Q) for elastic scattering from 0.2Å1 to 10Å. The time-of-flight data colec tion is automatic, utilizing either a multichannel ana lyzer or a small computer. The spectrum is continu ously observable on a scope and the data can be printed out on paper tape or on a typewriter. A spe cially designed sample cryostat is available for spec trum measurements on solid and liquid samples be tween 5 and 300K.

Applications: The spectrometers can be used wide. in the study of the dynamics of liquids and solic Some applications include the study of crystal and molecular dynamics of solids, vibrational spectra glasses, hydrogen diffusion in metals, orientationa disorder and relaxation processes in polymers and molecular crystals, and the dynamics of liquids.

Availability: Instrument time can be scheduled to appropriate experiments or projects of NBS sta after the proposed measurements are reviewed by the Users Committee for these facilities. Outs.c users can also be accommodated depending type of measurements and available resources.

on the

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Capabilities: The facility consists of twelve rods containing Co mounted in a circle on a plate at the bottom of a water pool 10 feet deep. The dose rates available range from about 2 x 106 rad/h (in carbon) at the center of the source array to about 2 x 103 rad/h near the edge of the mounting plate as of February 1974; these values decrease by about 10% per year. Samples as large as 5 cm high by 5 cm in diameter can be given reasonably uniform doses at the center position of the source array. Samples may be irradiated under various atmospheric conditions and over a wide range of temperatures.

Applications: This facility may be used to study the effects of gamma radiation on various materials such as polymers and electronic components. It may also be used as a standard calibration source for calibrating different types of radiation dosimeters such as thin polymer dye films.

Availability: Generally available to NBS personnel or
qualified guest scientists on a scheduled basis.
Contact: J. C. Humphreys, Applied Radiation Division,
Room C216, Radiation Physics Building, phone 301-

921-2201.

Transmitter buildings and antennas of WWVL, WWVB, and WWW at Fort Collins, Colorado.

WWVL VLF

BROADCAST STATION

WWWL is an experimental very-low-frequency (VLF) radio station located on the same Ft. Collins, Colorado, site as radio stations WWV and WWVB. Prior to July 1, 1972, it was operated by the Time and Frequency Division on a regularly scheduled basis to provide stable and accurate frequencies and timing information referenced to the NBS primary standards. Various combinations of 1-3 timeshared carrier frequencies were transmitted in the region of 20 kHz. Regular scheduled broadcasts were terminated as of July 1, 1972.

Capability: Approximately 2 kW radiated power; multiple carrier frequencies (timeshared) in the region of 20 kHz; carrier frequencies and phases can be controlled relative to NBS primary standards. Applications: Propagation research at VLF; frequency and time dissemination via multiple VLF carriers. Availability: Operation of the WWVL facility is the responsibility of the full-time Ft. Collins field site staff. Installation, maintenance, and monitoring of any special equipment involved in special experiments by other government agencies must be arranged with Mr. Viezbicke or the Engineer in Charge at Ft. Collins, Mr. J. Stanley.

Contact: P. Viezbicke, Chief, Frequency-Time Broadcast Services Section, Radio Building, Room 4030, NBS Boulder, Colo. 80302. Phone 303-499-1000 ext.

3453.

SPECIAL

ANNOUNCEMENTS
ON WWV/WWVH

Radio stations WWV in Ft. Collins, Colorado, and
WWVH in Kekaha, Kauai, Hawaii, are operated by the
Time and Frequency Division of NBS for the dissemi-
nation of standard frequency and time information.
Transmissions are on a continuous basis, simultane-
ously on 2.5, 5, 10, 15, and 20 MHz from both sta-
tions. In addition, WWV also transmits at 25 MHz. Es-
sentially worldwide coverage is achieved.

Capability: In addition to the primary time and frequency information provided, the WWW and WWVH formats include 45-second segments every other minute, most of which can be made available on a subscription basis to other government agencies for dissemination of official and public service information. Each prerecorded voice announcement will be repeated once per hour and will appear on all transmitted frequencies. A wide variety of commercial receivers are readily available that provide adequate reception.

Applications: Presently, voice announcements have been arranged for marine weather advisories by NOAA, geoalert messages by NOAA, radio propagation forecasts by the Office of Telecommunications, and Skylab-related information by NOAA. Decisions regarding suitability of proposed announcements for inclusion in the WWV/WWVH format will be the responsibility of NBS.

Availability: All segments except those reserved for NBS use, the semi-silent period, and those presently in use by other agencies are available. The content of all announcements accepted for inclusion in the broadcast formats will be the responsibility of the sponsoring agency and must be transmitted to the Ft. Collins or Hawaii sites by teletype or other suitable means. The permanent station staff will be responsible for prerecording the information supplied (if necessary) and for arranging for broadcast of the information at the proper times. Provisions can be made for a reasonable frequency of updating of the material broadcast.

Literature: NBS Frequency and Time Broadcast Services, Viezbicke, P. O., Nat. Bur. Stand. (U. S.) Spec. Publ. 236 (May 1973).

Contact: P. Viezbicke, Chief, Frequency-Time Broadcast Services Section, Radio Building, Room 4030, NBS Boulder, Colo. 80302. Phone 404-499-1000 ext. 3453.

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This high-accuracy spectrophotometer, with good sensitivity and linearity, will check the photometr scale accuracy of the transmittance of either solid or liquid filters used in commercial spectrophotometers Capability: The single-beam spectrophotometer capable of measuring transmittance (T) values or solid and liquid materials to within an uncertainty one part in 10 T units. It consists of a constant radation source (stability 7 parts in 10), a double mono chromator, adequate sample holders (one being automated through computer interfacing), and an averag ing sphere with photomultiplier tube assembly. The latter is connected to a digital voltmeter; data acqu sition and presentation is performed in a computer

Applications: Spectrophotometric (colorimetric) ana ysis is the predominant technique for bioclinical ex

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