title: The measurement of the depth of a point source of a radioisotope from gamma ray spectra.
abstract: The spectrum of the scattered radiation from a 'point' source of 99Tcm located within a slab of tissue-like material has been studied with a 19-phototube gamma camera, a 7.5 cm x 7.5 cm sodium iodide detector and a Ge(Li) counter. Both backscatter and forward scattered radiation contribute to the spectra observed; 'infinite' backscatter is achieved at a thickness of 8 cm. The scattered radiation can be used to estimate the thickness of the overlying material. The scatter from 133Xe and 51Cr was also measured. The depth of a source could usually be determined to within a few millimetres from the proportion of scatter in the spectrum; it was more accurate with the 51Cr (320 keV) than with the lower-energy photopeaks of the other two isotopes. The variation in the spectrum as the source moved across the field of the gamma camera was recorded.
mesh_terms: D002860:Chromium Radioisotopes / Q000032:analysis*; D005720:Gamma Rays; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D012542:Scattering, Radiation; D013057:Spectrum Analysis / Q000379:methods; D013667:Technetium / Q000032:analysis*; D014980:Xenon Radioisotopes / Q000032:analysis*
chemical_list: D002860:Chromium Radioisotopes; D014980:Xenon Radioisotopes; D013667:Technetium