Efficiency calibration and coincidence factor measurements for well HPGe detector

BackgroundWell-type HPGe detectors have the advantage of high detection efficiency and are commonly used for measuring small-sized samples. Coincidence correction is necessary in the measurement process, but such measurement data are rarely reported.PurposeThis study aims to determine the detection efficiency curve and coincidence correction factors of well-type HPGe detectors.MethodsFirstly, monoenergetic γ-ray nuclide standard sources including ²⁴¹Am, ¹⁰⁹Cd, ⁵⁷Co, ¹³⁹Ce, ⁵¹Cr, ¹¹³Sn, ⁸⁵Sr, ¹³⁷Cs, ⁵⁴Mn, ⁶⁵Zn, and ⁴⁰K were used to calibrate the full-energy peak detection efficiency of well-type HPGe detector in both top-mounted and in-well measurement modes. Then, standard sources of ⁶⁰Co, ⁸⁸Y, ¹³¹I, ¹³⁴Cs, ¹⁵²Eu, and ¹³³Ba with known activities were prepared to measure the coincidence correction factors. Finally, the relationship between coincidence correction factors and sample height as well as sample activity was investigated.ResultsThe efficiency value obtained using ¹³⁹Ce differs from the numerical fitting result by up to 49%. The activity measurement results are significantly influenced by the coincidence effect with smaller sample heights resulting in larger coincidence correction factors. When the sample height is 0.5 cm, the coincidence correction factors for the 563.23 keV and 604.70 keV γ-ray full-energy peaks emitted by ¹³⁴Cs reach 8.00 and 3.01, respectively. When the sample activity exceeds approximately 1 000 Bq, the contribution of random coincidence to the total coincidence correction factor gradually increases, and the coincidence correction factor for the 80.19 keV γ-ray full-energy peak increases by 10% when the activity of ¹³¹I increases from 1 300 Bq to 6 300 Bq.ConclusionsFor well-type HPGe detectors with high detection efficiency for low-energy photons, ¹³⁹Ce should be used with caution in efficiency calibration due to potential X-ray and γ-ray coincidence effects. Coincidence correction is essential for accurate activity measurements in well-type HPGe applications, particularly when measuring cascade-decay nuclides with small sample geometries or high activities. The measurement data provide practical guidance for selecting appropriate calibration sources and establishing correction procedures.