Efficiency calibration for HPGe detector by Monte Carlo efficiency transfer method

In this paper, the Monte Carlo efficiency transfer method was used to calibrate the full energy peak efficiency (FEPE) of a coaxial p-type HPGe detector. The gamma standard radioactive sources including 22Na, 54Mn, 57Co, 60Co, 65Zn, 109Cd,133Ba, 137Cs, 154Eu, 207Bi, 241Am were measured at different positions on-center of detector with the distance of 5, 10, 15, 20, 25 cm. Besides, a cylindrical sample containing standard mixed nuclides solution was also measured at surface of the detector. The experimental FEPE curves as function of gamma energy for these geometries were determined with the coincidence-summing corrections. A HPGe detector model based on the specifications of manufacturer was built to directly calculate the FEPE for the geometries by Monte Carlo simulations with MCNP6 code. However, these simulated FEPEs show a quite high discrepancy from experimental FEPEs. Then, the FEPEs were calculated by the efficiency transfer method with the efficiency curve for point source at distance of 25 cm as the reference data. A good agreement was obtained between the calculated results by the Monte Carlo efficiency transfer method and experimental results. The comparisons between experimental and calculated FEPE showed that the relative deviations were mostly within +/-4% in the energy range of 53-1770 keV.

Calibration of NaI (Tl) cylindrical detector using axially shifted radioactive cylindrical sources

In this article, the full energy peak efficiency of NaI detector using non-axial cylindrical sources is calculated by using a new efficient theoretical approach. This approach depends on using the efficiency transfer method and analytical calculations of the average path length of a gamma photon inside the source to the detector system. Measured efficiencies made by using 152Eu aqueous radioactive cylindrical sources with volumes 25 ml and 400 ml. Comparing calculated efficiencies to the measured one showed good agreement enabling the validation of this approach.

Calculation of NaI(Tl) detector full-energy peak efficiency using the efficiency transfer method for small radioactive cylindrical sources

A direct analytical mathematical method is introduced to calculate the efficiency of gamma ray cylindrical detectors. The efficiency expression is deduced through a straightforward mathematical approach. The presented method is based on the accurate analytical calculation of the average path length covered by the photon within the detector's active volume, effective solid angle, and the efficiency transfer method in an integral form, so as to obtain a simple formula for the detection efficiency. In addition, the self-attenuation coefficient of the source matrix, the attenuation factors of the source container (with a radius smaller than the detector radius) and the detector housing materials are also treated by calculating the average path length within these materials. 152Eu aqueous radioactive sources covering the energy range from 121 keV to 1408 keV were used. Remarkable agreement between the measured and the calculated efficiencies was achieved, with discrepancies less than 6 %.

Modeling the impact of uncertainty in detector specification on efficiency values of a HPGe detector using ANGLE software

The objective of this study is to model the impact of uncertainties in the engineering specifications of a typical p-type HPGe detector on the efficiency values when the measured soil sample is in contact geometry with the detector. We introduce a parameter named the normalized sensitivity impact which allows a comparative analysis to be made of the impact of the detector specification uncertainties and develop a correction factor table for the most important parameters. The areas of the detector most susceptible to error were found to be the crystal geometry, vacuum layer above the crystal and the bulletizing radius. In all cases the major impacts were mathematically modeled - for the first time - and found to vary either quadratically or logarithmically over the energy range of 180 keV to 1500 keV. Finally, we propose a set of detector characterization values that may be used in ANGLE for generating a reference efficiency curve using the efficiency transfer method inherent in this software. These values are to be used with the understanding that their uncertainty impact on the full-peak efficiency though not very significant in this counting arrangement, is not non-zero.