OPTIMUM X-RAY YIELDS IN BETA-EXCITED X-RAY SOURCES
ARMY MEDICAL RESEARCH LAB FORT KNOX KY
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An investigation was conducted to systematically investigate the influence of source physical conditions on the characteristic X-ray yield in beta-excited X-ray sources. The K X-ray yield excited by beta-particles in various target materials increased with increasing target thickness up to a maximum, after which the yield decreased because of X-ray absorption by target material. Optimum K X-ray yields were noted for P32 beta-particles at target thicknesses of about 77, 180, and 280 mgsq cm, respectively, for Sn, Ta, and Pb targets. Sn, Ta, and Pb target thicknesses of about 80,205, and 310 mgsq cm, respectively, were found to give optimum K X-ray yields for Sr90 - Y90 betas. The K X-ray intensities were increased by from 110 to 160 percent by the addition of source backing of same thickness as that providing maximum X-ray yields. Increase of backing to a thickness greater than that required to absorb maximum beta energies further increased maximum X-ray intensities from 25 to 50 per cent. Increased K X-ray yield efficiency extends the use of these sources to certain practical applications in low energy region below 100 kev where no suitable gamma-emitting isotopes presently exist. It is recommended that source physical conditions presented in this study be used, along with image intensifying systems, to extend the possible use of beta-excited X-ray sources to certain practical applications where increased X-ray intensity is desired.
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