Subnanosecond timing with a planar Ge(Li) detector

Abstract

The shape distribution of charge pulses obtained by uniform γ-irradiation of a 0.25 cm 3 planar Ge(Li) detector with a surface barrier window was studied. Leading-edge time resolution curves obtained with a plastic scintillation counter as time reference showed a strong Ge(Li) late tailing effect which was only partially reduced by the rise time compensation due to Chase. For a combination of the latter method and pulse shape selection time resolution curves were studied for different fractional numbers of all full energy events. By using about one half of all events the Ge(Li) late slope was improved one order of magnitude. For the 511 keV annihilation γ-ray from 22Na a fwhm time resolution of 1.1 ns and a Ge(Li) late T 1 2 slope of 0.13 ns over more than three decades were obtained. The time resolution was studied for different enrgies. The interaction number percebtage by total absorption for some energies are calculated and the influence on the pulse shape is discussed.