Balloon flight test of pulse shape discrimination (PSD) electronics and background model performance on the HIREGS payload

We flew a prototype of the INTEGRAL/SPI PSD electronics with a narrow-bore coaxial Ge γ-ray detector on the January 1998 Antarctic balloon flight of the HIREGS payload. The first goal for this test flight was to demonstrate the performance of the PSD electronics in a radiation background and space environment similar to that in which SPI will operate, which was successfully demonstrated. The second goal was to measure the fraction of the background due to localized β−-decays, and to validate the model used to predict SPI's background and the sensitivity improvement due to the PSD background rejection. Our background measurements show good agreement with the models developed for SPI, and strongly support the expected improvement in sensitivity due to PSD on SPI.