Improving Calibration Methods for Gamma Detectors Based on Refined Quantum Yields of ²³⁵U Gamma Lines

Broad Energy Germanium (BEGe) detectors, such as the BE6530, are widely used in high-resolution gamma spectrometry for precise uranium material analysis. Accurate calibration of these detectors requires reliable efficiency curves based on gamma lines of uranium isotopes. Standard methods often use lines from ²³⁵U, ²³⁴mPa, and ²²⁸Th, but in close-geometry measurements, cascade summation effects introduce systematic errors that distort peak intensities and affect results.

To minimize these errors, we propose an approach based on independent, non-cascading gamma lines of ²³⁵U in the 200–350 keV range, where summation effects are reduced and quantum yields can be reliably refined. Experimental measurements were performed using CRM-146 uranium reference material and NBL043 and NBL041 standards with different shielding configurations and source-detector distances simulating "long", "medium", and "close" geometries.

In parallel, Monte Carlo simulations in GEANT4 and MCNP5 provided theoretical efficiency curves and validated the experimental results. The comparison showed discrepancies up to 90% between some quantum yields in Nuclear Data Sheets and measured values, emphasizing the need for data refinement. The updated quantum yields and improved calibration methodology significantly enhance the precision of uranium material characterization in challenging measurement conditions. These results support applications in nuclear forensics, export control, uranium age-dating, and provide input for future nuclear data evaluations.