Challenges and techniques to effectively characterize the efficiency of broad-energy germanium detectors at energies less than 45 keV

With the now common availability of large-volume thin-window germanium detectors, it is possible to routinely measure very low energy (< 45 keV) gamma and X-rays while maintaining good sensitivity for high-energy gamma rays. The effective calibration of such detectors down to these low energies is often problematic or not possible because of the lack of calibrated sources or knowledge of the source geometry. New methods have been recently developed that extend Canberra's ISOCS/LabSOCS mathematical efficiency computation methods down to energies as low as 10 keV. Key to these developments is the capability to characterize the efficiency versus spatial location of a detector at the factory and thus eliminate the requirement to have "in the field" low-energy source standards. In this paper, the challenges for performing reliable efficiency characterizations below 45 keV and techniques developed to overcome these challenges are discussed. Response characterization results are presented for various types of low-energy and broad-energy detectors manufactured by Canberra.