Design Criteria for Wide Range Gamma Radiacs Using Semiconductor Diode Detectors

The report covers the application of silicon semiconductor detectors to a wide-range, gamma-ray doserate meter using the detectors in a pulse counting mode. It reviews pertinent circuit and detector characteristics that establish the doserate ranges that can be covered, the energy dependence to be expected from both large lithium-drifted detectors and very small silicon junction diodes, and finally the stability requirements imposed on the electronics by the pulse mode of operation. Methods of tailoring the photon energy response of semiconductor detectors are reviewed. Particular attention is given to the effect on design of amplifier and detector noise and variations in the noise level. One example of a combination of detectors to cover the doserate range from 0.2mR/h to 2000 R/h is shown. The report supports the conclusion that it is practical to make a survey meter, using silicon semiconductor detectors, that covers both the health physics and high doserate ranges of interest in military radiac design.