Moderated-neutron pulse shapes

Conference · Thu Dec 31 23:00:00 EST 1981

OSTI ID:6755152

Taylor, A D; Russell, G J; Meier, M M; Robinson, H

The time dependence of the neutron pulse from hydrogeneous moderators is well known in the slowing down region. The full width at half maximum, ..delta..t/sub 50/, behaves as 2/..sqrt..E when time is measured in ..mu..s and energy in eV. The shape of the pulse throughout the slowing down region is a universal function of vt, phi(v,t) = (..sigma../sub s/vt)/sup 2/ exp (-..sigma../sub s/vt). In this equation, v is the neutron velocity, ..sigma../sub s/ the macroscopic cross section of the moderating material and t is time. This infinite medium result is found to hold well even for small hydrogeneous moderators and departures from this behavior for reflected moderations are understood. Measurements of the time dependence have been made in the thermal region but no specific parameterization has been given. An empirical description is used in powder profile refinement but this has no physical basis. The time behavior depends strongly on the material and size of the moderator, the reflector and decoupler. Monte Carlo calculations have given some information on pulse shape, but are dependent on details of scattering kernels used and are difficult to perform for other than simple moderators. As condensed matter experiments on pulsed neutron sources become more sophisticated, information will be needed on the shape of the thermal pulse in addition to ..delta..t/sub 50/. In this paper, we attempt to find some guidelines to the time behavior of moderated neutron spectra in the thermal region.

• Research Organization: Los Alamos National Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6755152
• Report Number(s): LA-UR-82-2648; CONF-8206118-7; ON: DE83000665
• Country of Publication: United States
• Language: English

Related Subjects

654003* -- Radiation & Shielding Physics-- Neutron Interactions with Matter
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BARYONS
CARBON
DIFFUSION
ELEMENTAL MINERALS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY DEPENDENCE
FERMIONS
GRAPHITE
HADRONS
MINERALS
MODERATORS
NEUTRAL-PARTICLE TRANSPORT
NEUTRON SOURCES
NEUTRON SPECTRA
NEUTRON TRANSPORT
NEUTRONS
NONMETALS
NUCLEONS
PARTICLE SOURCES
PULSED NEUTRON TECHNIQUES
PULSES
RADIATION SOURCES
RADIATION TRANSPORT
SLOWING-DOWN
SPECTRA
THERMAL NEUTRONS
TIME DEPENDENCE
WAVELENGTHS