Fast Burst Reactor Neutron Damage in Silicon Transistors

An experiment was performed to assess the magnitude of the differences in neutron damage to silicon transistors under various conditions encountered in fast burst reactor testing. Transistors were subjected to free-field pulse and free-field power run exposures, and to exposures shielded by lead and by paraffin. These tests provided data to compare to damage results obtained under routine test conditions, i.e., relatively unperturbed field but with the experiment table in place. Fission foils and an activation foil were exposed with each group of transistors. The objectives of the experiment were: 1) to determine if perturbations in the reactor testing environment would produce measurable differences in the relative damage in silicon transistors--greater than the statistical variations characteristics of the test groups, and 2) to determine if the observed differences in damage could be correlated with the results of fission and activation foil neutron fluence measurements. Neutron exposures were performed at the White Sands Missile Range (WSMR) Fast Burst Reactor (FBR). Thin fission foils were exposed adjacent to lexan plastic discs to record the resulting fission tracks. The fission foils were exposed inside cadmium shields which were placed inside 10B shields. Sulfur pellets were exposed both inside and outside the boron shields. The fission track and sulfur counter data were evaluated using techniques similar to those specified in ASTM standard procedures. Relative silicon damage measurements were obtained by exposing groups of carefully characterized transistors.