Detection efficiency calibration for an array of fourteen HPGe detectors

Simulation of radon detection efficiency with small pulse ionization chamber based on Geant4

Radon measurement is crucial in assessing the damage to the human body caused by natural radiation. Pulsed ionization chambers are effective for real-time radon measurement and have widespread applications in other radiation techniques. However, due to practical constraints such as limited space and portability concerns, it becomes imperative to consider not only the detection efficiency but also their ease of transportation. This work utilizes the Geant4 Monte Carlo simulation toolkit to characterize the detection models of small cylindrical and flat plate-type pulsed ionization chambers, and carry out a simulation study to analyze the three crucial factors that influence detection efficiency, including the geometry of the chamber, electrode size, and operating temperature. The results indicate that the cylindrical pulse ionization chamber, with a length of 8 cm and radius of 2 cm, has the best detection efficiency and portability in terms of geometric dimensions, achieving a detection efficiency of (58 ± 4)%. Meanwhile, the flat plate pulse ionization chamber, with dimensions of 7 cm in length and 3 cm in width, achieves the best detection efficiency and portability, with a detection efficiency of (54 ± 3)%. In terms of electrode wire size, the cylindrical ionization chamber electrode wire with a length of 7 cm and a radius of 2.5 mm was optimal with a detection efficiency of (59 ± 4)%. In terms of operating temperature, the detection efficiency of the flat-plate pulsed ionization chamber was the highest at 30 °C, which was (58 ± 4)%, and that of the cylindrical pulsed ionization chamber was the highest at 20 °C, which was (63 ± 4)%. By analyzing the influencing factors of the detection efficiency of the pulsed ionization chamber, it has a certain reference value and guiding significance for the research and design of small pulsed ionization chamber detectors for radon measuring instruments.

Determination of detection efficiency on HPGe detector for point-like and volumetric samples based on Geant4 simulations

Production of medical isotopes has recently been developed at the Institute of Modern Physics (IMP) in China and many aqueous samples containing produced radioisotopes at wide range of volume were generated. Evaluation of radionuclidic purity and quantification of radioactivity for these samples are of significant importance, especially for medical purpose. High purity germanium (HPGe) detectors and gamma spectrometry are widely used in radionuclidic purity evaluation due to the high energy resolution. However, radionuclidic purity assessment and determination of radioactivity cannot be accurately conducted by using the HPGe detector installed at Laboratory of Nuclear Chemistry in IMP due to the lack of competent calibration standard sources. Therefore, an efficient method based on Geant4 simulation was proposed to calculate the detection efficiency curve for samples with different geometry, composition and source-to-detector distance. A set of efficiency data measured with a point-like standard source containing multi-radionuclides was used to determine the dimension of germanium crystal and thickness of dead layers. Afterwards, a point-like and 3 volumetric standard sources (5 ml, 10 ml and 20 ml, respectively) containing 152Eu were measured at 5-50 cm source-to-detector distances. The EFFTRAN code was applied to calculate the correction factor of coincidence summing for all measurements. The full energy peak (FEP) efficiencies with energy range of 121-1408 keV were calculated and compared with the values obtained from simulations. The simulated FEP efficiency values were in good agreement with experimental results, which illustrated a satisfactory precision of the Geant4 simulations. The feasibility of obtaining detection efficiency for point-like and volumetric samples by means of Geant4 simulations was confirmed. This method can be applied to address the efficiency problem caused by sample geometry and composition.