Application of a silicon drift detector to measuring internal conversion electrons and analysis of their spectra

Small-volume, low-capacitance semiconductor X-ray silicon drift detectors (SDDs) have an excellent ability to resolve closely spaced X-ray lines. But the application to electrons is less known. We designed a detector system and performed spectrometry using SDDs for radionuclides emitting mono-energetic internal conversion electrons (ICEs) with energies from 129 keV to 656 keV. The system is compact, maintains simple readout electronics, and provides high-resolution measurements of ICEs without cooling to liquid nitrogen temperatures and without bulky lead shielding. Preliminary measurements using Cs-137 and Xe-131m are conducted to verify that SDDs are suitable as ICE spectrometers. Unlike that of X/gamma spectrometry, the shape of the ICE spectra is a non-Gaussian distribution with apparent kurtosis. Therefore, a Pearson IV distribution function combined with a Levenberg-Marquardt fitting algorithm is utilized to analyze the ICE spectra quantitatively. The ratios of the net counts of ICE peaks for Cs-137 and Xe-131m as measured using SDDs with these fitting approaches are consistent with those reported in literature with a relative deviation of less than 3.4%.