Neutron Thermalization in a Heavy Moderator with an Absorption Resonance

Technical Report · Tue Mar 15 04:00:00 EST 1960

DOI:https://doi.org/10.2172/4184609· OSTI ID:4184609

Cohen, E. R. ^[1]; Moore, M. N. ^[1]; Vaughan, E. U. ^[1]

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1. North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.

The neutron velocity spectrum resulting from interaction of a high- energy neutron source with a spatially infinite, heavy gaseous moderator is obtained by solution of the Wilkins equation for the case of 1/v absorption cross section plus a single sharp resonance. The resonance is assumed to be narrow enough so that variations in the flux through the resonance are small with respect to the average flux in the resonance, yet broad with respect to the average energy loss per collision. The resonance escape probability and the effective resonance integral are defined and calculated. It is shown that the effect of the thermal motion of the moderator on the effective resonance integral can be expressed, in first order, as a correction to the mean logarithmic energy loss per collision. This correction, which can be described as the contribution of energy transfer from moderator to neutron, is the same as the one proposed by Cohen, and increases the resonance integral by ten per cent even for resonance energies as high as 20kT.

• Research Organization: North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• DOE Contract Number: AT(11-1)-GEN-8
• NSA Number: NSA-14-010178
• OSTI ID: 4184609
• Report Number(s): NAA-SR--4059
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
ABSORPTION
CROSS SECTIONS
GASES
MATHEMATICS
MODERATORS
NEUTRON FLUX
NEUTRONS
RESONANCE
RESONANCE ESCAPE PROBABILITY