Method for unfolding multiplet regions of X- and γγ-ray spectra with a detection efficiency constraint avoiding inflecting the peak shapes for correction results

To unfold multiplet regions in one-dimensional spectra measured on a multi-channel spectrometer with a high-purity germanium detector, constraints such as branching ratios and detection efficiency variation in the region should be used during fitting for more reliable and stable results. Experiments revealed that the thickness of the absorber material between the source and the detector can dramatically affect the detection efficiency, but no effect on peak width was observed at 0.1-eV resolution in a Monte Carlo simulation. Based on this shocking result  , an iteration loop method using a detection efficiency constraint was developed and applied to unfolding of a multiplet containing 24 X- and γγ-rays. Peak areas for the 24 rays agreed very well with real areas within statistical error. The method can be used as a reference to unfold other spectra and we suggest that a detection efficiency constraint should be taken into account during multiplet unfolding and with a correction method without inflecting the peak shapes.