Tunable Gamma-Rays in a Thermal Fission Environment for Microelectronics Testing

Abstract

Radiation testing of microelectronics is essential for systems operating in space or nuclear environments, but it is both time-intensive and costly. Qualification as a radiation-hardened system by the United States Government typically requires exposure to 50–2000 Rad(Si)/s total dose rate of Co-60 and 1 MeV-equivalent neutron fluence. Domestic testing capacity cannot meet current demand, with some facilities booked up to two years in advance. Early-stage designs frequently fail initial testing, necessitating redesigns that further extend development timelines.

This work proposes a new method to produce gamma-rays with tunable energy in a thermal fission environment and allow the use of easier to access low power thermal research reactors to provide earlier, lower-cost radiation screening during the design process. We investigate the use of test casings composed of pure metals or metal-paraffin composites for tuning the thermal fission neutron spectrum to maximize gamma production through carefully selected (n,γ) reactions. The method is verified using high-fidelity MCNP6.3 simulations to model these casings and evaluate dose deposition in silicon within the Purdue University Reactor Number One (PUR-1). Materials such as copper, indium, and cadmium in sheet form and suspended in paraffin wax were found to increase gamma energy deposition in silicon by up to 105% relative to the control PUR-1 fission spectrum. These results support the development of a physical irradiation experiment at PUR-1 to validate the Monte Carlo predictions.