Gamma Dosimetry by the Microplasma Phenomenon

The feasibility of employing commercially available, microwave P-N avalanche diodes as gamma radiation dosimeters was investigated. The detection method used to determine the magnitude of the radiation dose consisted of measuring the microplasma pulse counte-rate before and after the irradiation. The feasibility of this approach was established. The technique that was determined as suitable fcr this purpose consists of recording the peak on the pulse count-rate versus diode noise voltage curve. This count-rate peak was found to vary linearly with the gamma radiation dose between two dose limits, both of which are determined from the physical characteristics of the diode used. Three types of microwave diodes were used, and criteria were developed for selecting the most efficient microwave diode size for the radiation dose range of interest. In the course of the investigation it was also shown that the defect center introduction rate was dependent upon the physical size of the dosimeter for devices in the size range of the avalanche diodes used in this study. The specific diodes used had a Junction area range of from 0.6×10-4 to 7×10-4 cm2. By introducing the diode size as a variable in the damage data equation it was possible to obtain a reasonable correlation with silicon radiation damage data from the period 1963 to 1967. The size of the microplasma in the avalanche region was estimated from the data of this investigation and the estimate was found to correlate well with experimental data from the mid-1960´ s.