INELASTIC SCATTERING OF NEUTRONS FROM VERY COLD MATERIALS

Technical Report · Fri Sep 16 00:00:00 EDT 1960

OSTI ID:4080373

McReynolds, A W; Whittemore, W L

An electron linear-accelerator pulsed-neutron source was used for studies of the neutron scattering precess at low temperatures, particularly for measuremerts where it was advantageous relative to a reactor source. Low temperature of the scathering mediuzn is of interest from two viewpoints. Certain aspeets of the lattice or liquid vibrational spectnam, panticularly its low energy end, are best observed through thermal inelastic scattering of very cold neutrons by phonon emission. At such low neutron energies, however, the cross section for such processes becomes very low; whereas, the cross section for phonon absorption becomes much greater. The latter processes must be suppressed by maintaining low sample temperature. Measuremerts on hydrogenous and other moderating materials are reported. A second necessity for measurements at low incident energies is an adequately irtense source of cold neutrons. Shch sources were previously obtnined by crystal filters transmitting only the weak low energy tail of the reactor thermal spectnam. A more satisfactory source in principle is a 4 to 20 deg K moderator in which the ertire spectrum reaches thermal equilibrium kT approximately 0.0003 to 0.0016 ev. In practice such sources were not available because of difficulties of installing a cryogenic device in the high flux region of a reactor, where radiation heating requires rapid heat extraction. The decrease of energy loss cross section at low energies also necessitated a substantially larger moderating volume than was required at approximately 300 deg K. Cold moderator sources may be advantageously investigated by the electron lirac, wlilch with 3 to 5 sigma sec 25-Mev pulses on lead targets produces bursts of 5 x 10/sup 10/ neutrons 120 times per second. The resultant source strensth of approximately lO/sup 16/ neutrons per second during the pulse gave flux intensities comparable to bursts from a reactor and chopper. Advantages include the fact that the region immediately around the neutron source is readily accessible for normal cryostatic apparatus, and there is negligible radiation heating, activation, or hazard. A series of investigations was carried out to determine the behavior as cold neutron sources of a number of comigurations of mederators, including H/sub 2/O, D/sub 2/0, CH/ sub 2/, CD/sub 2/, and ReO at temperatures of 4, 80, and 300 deg K. Similar measurements with H/sub 2/ are in progress. (auth)

• Research Organization: General Atomic Div., General Dynamics Corp., San Diego, Calif.
• NSA Number: NSA-15-012066
• OSTI ID: 4080373
• Report Number(s): GA-1690
• Resource Relation: Other Information: For presentation at the International Atomic Energy Agency Symposium on Inelastic Scattering of Neutrons in Solids and Liquids, Vienna, October 11-14, 1960. Orig. Receipt Date: 31-DEC-61
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

PHYSICS
ABSORPTION
ACTIVATION
BERYLLIUM MODERATOR
BERYLLIUM OXIDES
CARBON COMPOUNDS
CHOPPERS
CONFIGURATION
CROSS SECTIONS
CRYSTALS
CYLINDERS
DISTRIBUTION
EFFICIENCY
ELECTRON BEAMS
ENERGY
FILTERS
FREQUENCY
GAMMA RADIATION
GAMMA SOURCES
HEATING
HEAVY WATER
HEAVY WATER MODERATOR
HYDROGEN
HYDROGEN COMPOUNDS
INELASTIC SCATTERING
INTERACTIONS
IRRADIATION
LATTICES
LINEAR ACCELERATORS
LIQUIDS
LOW TEMPERATURE
MEASURED VALUES
MODERATORS
NEUTRON FLUX
NEUTRON SOURCES
NEUTRON SPECTROMETERS
NEUTRONS
NUCLEAR MODELS
NUCLEAR STRUCTURE
NUCLEAR THEORY
NUMERICALS
OPTICAL MODEL
OSCILLATIONS
PERFORMANCE
PHONONS
PULSE GENERATORS