High accuracy determination of relative full energy peak efficiencies for high resolution gamma-ray spectrometry.

Abstract

A method for the high accuracy determination of the relative full energy peak efficiency is established. Radionuclides which emit at least two gamma-lines for which the relative intensity can be found (from the decay scheme) to much better than 0.1% were used as calibration standards. Specifically, the 889 keV and 1120 keV lines of $\sp{46}$Sc, the 983 keV and 1312 keV lines of $\sp{48}$Sc, the 1173 keV and 1332 keV lines of $\sp{60}$Co, the 702 keV and 871 keV lines of $\sp{94}$Nb, the 558 keV and 725 keV lines of $\rm\sp{114m}$In, and the 1368 keV and 2754 keV lines of $\sp{24}$Na were implemented. The high accuracy calibration was taken to extend from the lowest line of $\sp{94}$Nb at 702 keV to the highest line of $\sp{60}$Co at 1332 keV, with the possibility of extension up to the 2754 keV line of $\sp{24}$Na, and down to the 558 keV line of $\rm\sp{114m}$In. An analytical expression, based on linear least squares fitting, was developed to describe the behavior of the relative efficiency curve in that energy range. As a result, the ability of predicting full energy peak relative efficiencies to within 0.1% (over most of the energy range) was demonstrated. The presented method is applicable in any measurement that requires the minimum calibration bias in the determination of reaction rate ratios. Applications in Neutron Activation Analysis (NAA), and in nuclear reactor dosimetry represent examples of such situations.