SIMULATIONS OF PULSE-SHAPE DISCRIMINATION (PSD) TECHNIQUES FOR BACKGROUND REDUCTION IN GERMANIUM DETECTORS

For modern, actively shielded, narrow aperture germanium detector (GeD ) spectrometers at balloon or spacecraft altitudes, the continuum back ground in the 0.2 to 2 MeV energy range is dominated by the beta(-) de cay of radioactive nuclei produced by the interaction of cosmic rays a nd secondary protons and neutrons within the detector. PSD techniques distinguish single-sire (primarily beta(-)-decay) from multiple-site ( primarily photon) events by analyzing the shape of the current pulse f ormed when the electrons and holes resulting from these energy deposit ions propagate through the detector. Through numerical simulation of t he charge collection process, we demonstrate that the effectiveness of PSD can be enhanced by optimizing detector geometry and external elec tronics. In particular, PSD results for closed-end coaxial detectors w ith standard (1.2 cm effective diameter) and narrow (0.6 cm diameter) inner bore, and for a true coaxial narrow-bore detector, are presented . With a newly developed PSD algorithm, improvements in sensitivity at 1 MeV of factors of 2.8 and 3.6 for the standard-bore and narrow-bore closed-end coaxial detectors, respectively, and 4.0 for the true coax ial detector, are predicted. (C) 1998 Elsevier Science B.V. All rights reserved.