Shielding Effects in Spaceborne, NaI Gamma-Ray Spectrometers

Radioactivity induced in detectors by cosmic rays and trapped protons limits the sensitivity of spaceborne gamma-ray spectrometers. In this paper 1-D transport calculations are used to analyse the influence of neutron shielding on the radioactive background induced in NaI by neutron capture reactions. It is found that the use of thermalising absorbers to surround central detector elements is in fact counter-productive. Full 3-D transport codes have been applied to the trapped proton case and verify both the absolute levels of this component and the negative influence of neutron shielding.