Determination of the effective sample thickness via radiative capture

Journal Article · Mon Sep 14 00:00:00 EDT 2015 · Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

DOI:https://doi.org/10.1016/j.nimb.2015.09.003· OSTI ID:1229843

Hurst, A. M. ^[1]; Summers, N. C. ^[2]; Szentmiklosi, L. ^[3]; Firestone, R. B. ^[1]; Basunia, M. S. ^[1]; Escher, J. E. ^[2]; Sleaford, B. W. ^[2]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Hungarian Academy of Sciences, Budapest (Hungary)

Our procedure for determining the effective thickness of non-uniform irregular-shaped samples via radiative capture is described. In this technique, partial γ-ray production cross sections of a compound nucleus produced in a neutron-capture reaction are measured using Prompt Gamma Activation Analysis and compared to their corresponding standardized absolute values. For the low-energy transitions, the measured cross sections are lower than their standard values due to significant photoelectric absorption of the γ rays within the bulk-sample volume itself. Using standard theoretical techniques, the amount of γ-ray self absorption and neutron self shielding can then be calculated by iteratively varying the sample thickness until the observed cross sections converge with the known standards. The overall attenuation provides a measure of the effective sample thickness illuminated by the neutron beam. This procedure is illustrated through radiative neutron capture using powdered oxide samples comprising enriched ¹⁸⁶W and ¹⁸²W from which their tungsten-equivalent effective thicknesses are deduced to be 0.077(3) mm and 0.042(8) mm, respectively.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC52-07NA27344; AC02-05CH11231; OMFB-00184/2006
• OSTI ID: 1229843
• Alternate ID(s): OSTI ID: 1246226
• Report Number(s): LLNL-JRNL-673901
• Journal Information: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Vol. 362; ISSN 0168-583X
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUMM MECHANICS
GENERAL PHYSICS
Prompt Gamma Activation Analysis (PGAA)
gamma-ray absorption
neutron attenuation
(n
γ) radiative capture
partial gamma-ray production cross sections