The goal of this work is to elucidate critical points of failure of the Front-End Digitizer (FrEnD) under neutron irradiation. These data will inform the design of future iterations of the FrEnD system to improve its tolerance to ionizing and neutron radiation. Circuitry that is hardened to ionizing radiation (gamma, protons, energetic heavy ions) has undergone significant study in the commercial sector, mostly for space flight applications. However, the effects of neutron irradiation on electronics is not well understood, although it is critically important for further developments in nuclear and high-energy physics applications. The proposed work will generate significant data for the performance of commercial-off-the-shelf (COTS) circuit components to neutron irradiation.
The current version of the FrEnD acquisition system is designed to multiplex and transmit signals from up to seven sensors located in a high-neutron, ionizing radiation environment over a single optical fiber. The FrEnD system is designed to improve signal fidelity while minimizing the need for penetrations into nuclear containment structures. In its present design, FrEnD uses low-cost COTS components, including junction-gate field effect transistors (JFETs), which are inherently resistant to ionizing (gamma) radiation. However, these JFETs' resistance to neutron radiation is unknown. To characterize the tolerance of the FrEnD system to neutron radiation, three JFET-based printed circuit boards (PCBs), each 12x15 cm, will be placed in an irradiation standpipe at the North Carolina State University (NCSU) PULSTAR reactor. During irradiation, the PCBs will be powered, input signals will be provided to the circuitry, and relevant test points will be monitored through wired (twisted pair) connections to a Saleae data acquisition system. Irradiation standpipes at the PULSTAR have customize-able neutron fluxes ranging from 10^7-10^12 n/cm^2/s and a diameter of 16 cm. To reach a total fluence of 10^14-10^15 n/cm^2, the experiment will run for eight hours per day over the course of five days for a total of 36 hours. Reactor downtime each day is desired to measure any possible annealing effects that may occur in our circuitry and the behavior produced by that recovery.
