Simple and accurate calibration technique for measuring γ-ray energies and Ge(Li) detector linearity

Abstract

A technique for precise calibration of Ge(Li) γ-ray spectrometers, which is particularly useful in studies of decay schemes, has been developed. The differential response of a multichannel analyzer is measured with a sliding pulse generator whose incremental nonlinearity is 0.005–0.01%. The integral of this response with respect to counts is a linear function of energy. With the use of two known γ-ray lines the calibration constant in counts/keV, and in turn, the energies corresponding to unknown γ-ray peaks can be determined. The technique is simple, fast and virtually automatic. The method was evaluated by measuring γ-ray energies (0.27–2.75 MeV) from ten sources. The results obtained agree with published values to within the measurement uncertainty of 40–110 eV. The accuracy of the technique depends on the linearity of the sliding pulser and the Ge(Li) detector. From a spectrum of 66Ga, measured energy intervals of 2 m 0 c 2 were examined as a function of γ-ray energy. The standard deviation of the eight 2 m 0 c 2 intervals was only 0.08 keV. It is therefore concluded that between 1 and 5 MeV the incremental non-linearity of the coaxial Ge(Li) detector is less than ±0.1 keV. Measurement uncertainties due to errors in the calibration standards, peak location, and the number of counts/channel in the differential response are discussed.