Calibration of Photographic Emulsions for Low Energy Electrons

Abstract

Measurements are reported for the dependence on energy of photographic darkening due to electrons of energies between 4.4 and 45 kev. For Ilford B-2 plates, in the linear density exposure region, the results can be expressed by the empirical formula D/Q/A=KEx. D is the photometric density, Q/A the exposure in electrons/mm2, E the energy in electron-volts; K and x are constants with the values (0.30±0.03)×10−12 and 1.45±0.05, respectively. The relationship for two other emulsions tested is complicated by the presence of surface coatings on the emulsions. Reproducibility of results is discussed. Results are given on density fluctuations due to granularity of Ilford and x-ray emulsions. The limit of sensitivity, using the L. and N. recording microphotometer with scanning beam 1.0 by 1.3 mm, is estimated at 450 electrons/mm2 of 40 kev energy for the x-ray emulsion and 680 electrons/mm2 for the Ilford plates. The latter is limited by photometric sensitivity.