Measurement Of The X-Ray-Induced Light Photons Emitted From Radiographic CaW04 Intensifying Screens

H. Roehrig; B. Lum; S. Nudelman; M. P. Capp; C. E. Dick

doi:10.1117/12.957117

6 July 1979 Measurement Of The X-Ray-Induced Light Photons Emitted From Radiographic CaW0₄ Intensifying Screens

H. Roehrig, B. Lum, S. Nudelman, M. P. Capp, C. E. Dick

Proceedings Volume 0173, Application of Optical Instrumentation in Medicine VII; (1979) https://doi.org/10.1117/12.957117
Event: Application of Optical Instrumentation in Medicine VII, 1979, Toronto, Canada

Abstract

For calcium tungstate intensifying screens employed in film-screen imaging systems, Coltman found that approximately 1000 light photons of average energy 2.7 eV were produced for each 50 keV x-ray absorbed. Of this number, he found that only about 55% are emitted from the output side of a 109 mg/cm² screen. We have developed a method based on counting single photons to determine this number for various thicknesses of calcium tungstate screens. Monoenergetic x rays in the energy range from 17-69 keV produce upon absorption, a shower of individual photon pulses which are detected by a low noise photomultiplier. After amplification and discrimination against the noise background of the phototube, the resultant pulses are counted in a 70 MHz scaler or a 150 MHz counter. The detection system has a pulse resolving time of less than 15 ns. The data are then corrected for the quantum efficiency of the detector and normalized to the number of absorbed x rays which is determined in a separate experiment. For calcium tungstate screens with thicknesses of 30, 50, 86, and 123 mg/cm², the average numbers of light photons emitted per absorbed x ray are measured for 8 x-ray energies between 17- and 69-keV. The values for 50 keV are less than the values found by Coltman. Studies of the causes of this discrepancy are in progress.

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H. Roehrig, B. Lum, S. Nudelman, M. P. Capp, and C. E. Dick "Measurement Of The X-Ray-Induced Light Photons Emitted From Radiographic CaW0₄ Intensifying Screens", Proc. SPIE 0173, Application of Optical Instrumentation in Medicine VII, (6 July 1979); https://doi.org/10.1117/12.957117

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