The Use of the Silicon Transistors as Damage Monitors in Reactor Neutron Metrology

Abstract

Measurements of neutron induced damage to silicon bipolar transistors using Cf-252 sources have been performed in order to establish a technique for use in fast neutron metrology. A general purpose n-p-n bipolar transistor (PN2222A) was chosen as the radiation damage monitor, and the change in inverse d. c. current gain before and after irradiation was chosen as the damage parameter for the measurements. A controlled annealing cycle after retrieval of transistors from the exposure and prior to gain measurements was carried out to overcome the problem of partial annealing of damage during exposure.

The main finding of the investigation was that the change in inverse d.c. current gain for transistors was a linear function of the fast neutron fluence up to 10¹⁴ n(l MeV)/cm². The damage coefficient, defined as the ratio of the measured damage parameter to the 1 MeV equivalent fluence, was found to be 4.95 x 10⁻¹⁶ ± 1.41% and 7.01 x 10⁻¹⁶±2.6% cm²/n(l MeV) for bare and D₂O-moderated Cf-252 spectra, respectively. High temperature annealing has also been tried at temperatures up to 180°C. This treatment has no effect on unirradiated transistors but removes about 66.7% of the damage from irradiated transistors.