High Resolution Ge (Li) Spectrometer for High Input Rates

A system was developed for obtaining γ-ray spectra with high resolution at high input rates. For rates up to 100 000 γ-ray events/sec in a 3.5 cm3 (13 mm thick) Ge(Li) detector, the FWHM at 1.33 MeV is 2–3½ keV and the spectral shift is no more than 0.1%. The amplifying chain, consisting of a cooled FET preamplifier and a simple main amplifier, is pole-zero compensated throughout. The amplifier produces unipolar pulses shaped with equal integrating and differentiating time constants of 1.2 μsec. The amplifier is followed by a two-diode baseline restorer, a pileup rejector, a linear gate, and an analog to digital converter. The salient features of the system are described and performance data are presented and discussed.