Long term background behaviour of LEGRI CdZnTe detectors: theoretical predictions and observations

Trapped protons are the main source of background in LEO orbits through the generation of unstable isotopes within the detectors and surrounding materials. Delayed radioactivity decays are one of the most important contributions to the observed background. Accurate modelling for LEGRI (Low Energy Gamma-Ray Imager) on-board MINISAT-01 mission has been performed using new experimental data together with two of the most widely used prediction codes (semiempirical expressions of Silberberg & Tsao and the GEANT/GCALOR package). Finally, Silberberg & Tsao expressions have been used to model the CdTeZn background behaviour for the long-term component. In this paper we present a comparative analysis of the experimental data obtained during the first two years of LEGRI operation with the results provided by our theoretical modelling. An unexpected good agreement is found. The fast increase of the background counting ratio in the first month followed by a early flat response for the rest of the operation time is very well reproduced by the theoretical model. These results also show the capability of the CdZnTe detectors to survive under high proton doses in space without degradation.