The Effects of Short Duration Neutron Radiation on Semiconductor Devices

Transistors, semiconductor diodes, and solid-electrolyte batteries were exposed to short duration, high-intensity neutron radiation from a U-235 critical assembly which was primarily a neutron source. The effect on these components was ascertained by comparing their principal parameters before and after exposure, and in several cases units of operating equipment utilizing these components were monitored during irradiation. Of the transistor electrical parameters altered by irradiation, most significant were the decrease in common emitter forward current gain (Beta) and the increase in collector diode reverse leakage current (Ico). The higher frequency units were less affected by neutron fluxes than were the audio transistors. High-frequency surface barrier transistors remained virtually undamaged by irradiation up to 1013 total neutrons per square centimeter, an exposure which rendered the audio units nearly useless. Semiconductor diodes suffered an increase in forward resistance and a decrease in back resistance in reasonable accord with the degree of neutron irradiation, while the solid-electrolyte batteries were not permanently affected. The results obtained are in reasonable agreement with those obtained by others who used pile-type reactors with much longer exposure times, thus indicating that the integrated neutron dosage is of primary significance rather than the rate of exposure. The degradation of performance of the operating equipment during irradiation was almost entirely attributable to changes in the semiconductor devices utilized therein.