Open AccessSmall-angle Compton Scattering to Determine the Depth of a Radioactive Source in Matter
Author(s) -
R.B. Oberer,
Clare A. Gunn,
L.G. Chiang,
R. E. Valiga,
J. A. Cantrell
Publication year - 2011
Language(s) - English
Resource type - Reports
DOI - 10.2172/1016162
Subject(s) - compton scattering , gamma ray , scattering , physics , radioactive source , attenuation , mockup , discontinuity (linguistics) , point source , detector , computational physics , uranium , optics , solid angle , nuclear physics , materials science , mathematics , mathematical analysis , composite material
A gamma-ray peak in a spectrum is often accompanied by a discontinuity in the Compton continuum at the peak. The Compton continuum results from Compton scattering in the detector. The discontinuity at a peak results from small-angle Compton scattering by the gamma rays in matter situated directly between the gamma-ray source and the detector. The magnitude of this discontinuity with respect to the gamma-ray peak is therefore an indicator of the amount of material or shielding between the gamma-ray source and the detector. This small-angle scattering was used to determine the depth of highly-enriched uranium (HEU) solution standards in a concrete floor mockup. The empirical results of the use of this small-angle scattering discontinuity in a concrete floor experiment will be described. A Monte Carlo calculation of the experiment will also be described. In addition, the depth determined from small-angle scattering was used in conjunction with differential attenuation to more accurately measure the uranium content of the mockup. Following these empirical results, the theory of small-angle scattering will be discussed. The magnitude of the discontinuity compared to the peak count rate is directly related to the depth of the gamma-ray source in matter. This relation can be described by relatively simple mathematical expressions. This is the first instance that we are aware of in which the small-angle Compton scattering has been used to determine the depth of a radioactive source. Furthermore this is the first development of the theoretical expressions for the magnitude of the small-angle scattering discontinuity