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.

I. Introduction

Secondary neutrons and slit-scattered protons that are produced during proton radiation testing of electronic devices may cause undesirable effects to components supposedly outside of the collimated proton beam. Unwanted neutrons can be produced by proton interactions in upstream collimators, shielding and all other beamline elements, or on high-density components on the test board itself. As these neutrons are produced over a large angular range, they can affect the operation of the test board, for example, if the neutrons strike a sensitive component near the device under test (DUT) but outside the expected proton beam. Similarly, slit scattering with large angles can send high-energy protons well outside of the expected irradiation area. The potential of these effects to disrupt single-event effect (SEE) testing is a common worry for testers when planning their data taking campaigns.