Resolution enhancement of coaxial, high-purity, Ge gamma-ray detectors

The enhancement of the energy resolution of high-purity, Ge (HPGe), gamma-ray detectors was studied. In particular, circuits which correct for ballistic deficit and charge trapping were analyzed. Also, an equation from which energy line shapes can be calculated for arbitrary charge trap distributions and spectroscopy amplifier peaking times was developed. The resolution enhancement circuits were studied over the energy range from 100keV to 10MeV and spectroscopy amplifier peaking times from lus to 12us. The charge trapping correction circuit improved the full-width-at-half-maximum (FWHM) resolution of a radiation damaged, HPGe detector from 4.3keV to 2.0keV at the 1.33MeV energy line. And, a ballistic deficit correction circuit improved the resolution of an HPGe detector from 12.1keV to 4.95keV at the 2.61MeV energy line and spectroscopy amplifier peaking time of 2us. The data also indicated the added importance of charge trapping correction at higher energies. For example, the resolution of a detector at 10MeV, which exhibited negligible ballistic deficit and charge trapping at 1.33MeV (spectroscopy amplifier peaking time = 12us), was improved from 7.3keV (calculated) to 5.6keV (extrapolated) when charge trapping and ballistic deficit corrections were used. For energies above approximately 800keV, an instrument which combined a gated integrator with a charge trapping correction circuit offered the best resolution.