A SEI-MEMPIRICAL EFFICIENCY CURVE FOR A GE(LI) DETECTOR IN ENERGY RANGE 50-KEV TO 1400-KEV

A semi-empirical method is given to obtain the relative full-energy-peak efficiency ε{lunate}γ of a Ge(Li) diode over the γ-ray energy range 50 to 1400 keV. The method is an extension of the work done by Freeman and Jenkin1) and accounts for both γ-ray attenuation in the materials present between a fixed source position and the intrinsic region of the diode and the saturation of the diode efficiency at low energies. The formula ε{lunate}γ ≈ T[ {τ+σQexp(-RE)} (τ+σ)][1-exp{-P(τ+σ)}], was fitted to the observed relative efficiency of a 2mm depleted Ge(Li) planar diode to an accuracy of 1 1 2% over the range 100 to 1400 keV and 4% over the range 50 to 1400 keV. Here T is the γ attenuation in materials outside the intrinsic region. τ and σ are the germanium photoelectric and Compton absorption coefficients respectively, E is the γ-ray energy, Q and R are constants determined from efficiency measurements and P is an effective depletion depth. The dependence of the shape of the relative efficiency curve on source-to-diode distance was examined using a 169Yb point source. © 1969.