Monte Carlo calculations of LANL graphite pile response functions

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Health Physics

OSTI ID:393960

Hsu, H H; Clement, R S ^[1]

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1. Los Alamos National Laboratory, NM (United States)

A Graphite Pile was built at Los Alamos National Laboratory in the early 1950`s to measure emission rates from neutron radiation sources using a BF{sub 3} proportional counter. The Pile was originally calibrated with a primary standard {sup 226}Ra/Be neutron source. The BF{sub 3} counter is inserted in the center of the Pile 138.5 cm above the ground surface, while neutron source position varies from 21 cm to 81 cm below the BF{sub 3} counter. In the past, it was assumed that neutrons emitted by a source would be totally thermalized by the time they reached the detector. Also, the detection efficiency was used for other neutron sources and the differences in energy spectra were not taken into account. Detailed Monte Carlo calculations were performed to determine Pile response functions for source-to-detector distances of 21 cm, 31 cm, 51 cm, and 81 cm. These response functions are then folded to energy spectra of ten different neutron sources: {sup 252}Cf, {sup 241}Am/F, {sup 241}Am/B, {sup 241}Am/Be, {sup 241}Am/Li, {sup 238}Pu/Li, {sup 239}Pu/Be, {sup 226}Ra/Be, Po/Be, and {sup 242}Cm/Be, whose neutron spectra are known. Results show that detection efficiencies are about 2.5 E-3 at the shortest distance (21 cm), and for different sources they can differ by 40% at that distance. Conversely, at the largest distance (81 cm), Pile response functions are relatively flat with respect to neutron energy. Moreover, detection efficiencies differ only by about 5%, but the absolute efficiency is about 2.0 E-4.

• OSTI ID: 393960
• Report Number(s): CONF-9607135--
• Journal Information: Health Physics, Journal Name: Health Physics Journal Issue: Suppl.6 Vol. 70; ISSN HLTPAO; ISSN 0017-9078
• Country of Publication: United States
• Language: English

Related Subjects

44 INSTRUMENTATION
INCLUDING NUCLEAR AND PARTICLE DETECTORS
EFFICIENCY
ENERGY SPECTRA
GRAPHITE
LANL
MONTE CARLO METHOD
NEUTRON SOURCES
RADIATION DETECTION
RADIATION SOURCES
RESPONSE FUNCTIONS