Small-angle Compton scattering used to determine the depth of a radioactive source in material and to estimate gamma-ray attenuation

• Small-angle Compton scattering causes a discontinuity at each gamma ray peak.
• The discontinuity contains valuable information about shielding material.
• It results only from scattering along the axis between the source and detector.
• The magnitude of the discontinuity is predicted by simple mathematical formulas.
• Experimental results validate small-angle scattering predictions.

Small-angle Compton scattering produces a familiar discontinuity in the background continuum at each gamma-ray peak in a spectrum. This discontinuity was previously considered a degradation of the spectrum that needed to be removed in order to determine the net peak count rate. This discontinuity actually contains valuable information about the amount of material between the gamma ray source and the detector. This information is useful in determining the amount of attenuation that the gamma rays undergo. Furthermore, the magnitude of the discontinuity is described by simple mathematical formulas.The use of small-angle Compton scattering was discovered while analyzing the amount of highly enriched uranium (HEU) absorbed in a concrete floor. An experiment using an HEU source and concrete tiles is presented demonstrating the agreement with theoretical predictions.