Neutral Particle Background in Cosmic Ray Telescopes Composed of Silicon Solid State Detectors

Abstract

The energy loss spectrum of secondary charged particles produced by the interaction of y-rays and energetic neutrons in silicon solid state detectors has been measured with a satellite-borne cosmic ray telescope. The products of these neutral-particle interactions are found to constitute a significant 'background' in typical spacecraft experiments designed to measure low energy cosmic rays. In the satellite measurements presented here two distinct neutral background effects are identified: secondary protons and alpha particles with energies of ≈2 to ≈100 MeV produced by neutron interactions, and secondary electrons with energies of ≈0.2 to ≈10 MeV produced by y-ray interactions. The implications of this neutral background for satellite measurements of low energy cosmic rays are discussed, and suggestions are given for applying these results to other detector systems in order to estimate background contamination and optimize detector system design. Our observations imply that the neutron induced background may be significant in many of the earlier quiet-time measurements of low energy cosmic ray protons and alpha particles in the so-called 'low energy turnup region'.