Simulation and Measurements of Collimator Effects in Proton and Neutron Radiation Testing for Single-Event Effects

During single-event effect (SEE) testing of electronic devices with collimated proton and neutron beams at accelerator facilities, support equipment is often located in close proximity to the beam. Background radiation in the area outside the nominal beam spot is created when the beam interacts with components of the beamline such as shielding, collimators, and monitoring devices, or when the beam interacts with high density elements of the devices under test. This background radiation can cause unforeseen and undesirable issues in the support equipment. At the TRIUMF Proton and Neutron Irradiation (PIF & NIF) facilities, an SRAM-based dosimeter was used to measure proton and neutron beam profiles. In some of these measurements, the beamline configuration was designed to enhance the background level. To better understand the processes that give rise to this background, and how it changes with the measurement position, beam energy, and beam type, these measurements are compared to FLUKA simulations of two of TRIUMF's beamlines. The simulated and measured beam profiles show a good general agreement over a range much wider than the beam spot size. For proton beams, the background is around 1% of the central beam intensity and the relative importance of neutron and slit-scattered protons changes with the distance from the final collimator. For the neutron beams studied, the background is dominated by neutrons and is around 30% of the central beam intensity whether or not collimators are used to manipulate the size of the beam spot.