High-purity germanium (HPGe) detectors are widely used in nuclear spectroscopy (e.g., neutron activation analysis) due to their high resolution. Resolution function of a GMX series coaxial detector system (model number GMX40P4-83) in the range of 40 keV to 1.46 MeV has been measured using standard
The use of germanium detectors has completely revolutionized gamma spectroscopy. The great superiority of the germanium system in energy resolution allows the separation of many closely spaced gamma-ray energies, which remain unresolved in the NaI(Tl) spectrum [
The detector used in this study was a GMX series HPGe coaxial detector system: the detector model number: GMX40P4-83; cryostat configuration: CFG-PG4-1.2; preamplifier model: A257N; HV filter model: 138 EMI. The resolution (FWHM) at 1.33 MeV, 60Co is 2.02 keV and peak-to-Compton ratio, 60Co is 59 : 1 and relative efficiency at 1.33 MeV, 60Co is 40%.The crystal has a diameter of 60.6 mm and length of 66.9 mm and also has a 0.3-micron Ge/B dead layer and 700-micron Ge/Li dead layer. The characteristics given by the manufacturers are shown in Figure
(a) HPGe detector (Ortec, PopTop, model: GMX40P4-83) used to measure and calculate the detector response function, (b) inner structure of the HPGe detector.
The overall energy resolution achieved in a germanium system is normally determined by a combination of three factors: the inherent statistical spread in the number of charge carriers, variations in the charge collection efficiency, and contributions of electronic noise [
The Gaussian width is related to the Full Width at Half Maximum (FWHM) by
Seven standard
Seven standard photon sources including eleven energies in the range from 40 keV to 1.460 MeV.
Radionuclide |
|
Half-life | Rad. type |
---|---|---|---|
Eu-152 | 0.040118 | 9.3116 hrs | X KA1 |
Am-241 | 0.059540 | 432.2 yrs | Gamma |
Ba-133 | 0.080997 | 10.52 yrs | Gamma |
Co-57 | 0.122060 | 271.79 days | Gamma |
Eu-152 | 0.244697 | 9.3116 hrs | Gamma |
Eu-152 | 0.344278 | 9.3116 hrs | Gamma |
Ba-133 | 0.356012 | 10.52 yrs | Gamma |
Cs-137 | 0.661657 | 30.04 yrs | Gamma |
Co-60 | 1.173228 | 5.2714 yrs | Gamma |
Co-60 | 1.332492 | 5.2714 yrs | Gamma |
K-40 | 1.460822 | 1.277 |
Gamma |
According to this work the author has extracted the following parameters in the GEB option to generate detector responses (Figure
Diagram of FWHMs versus measured gamma-ray energy spectra used to fit on
The experimental setup, detector and source, was simulated with the MCNPX Monte Carlo code [
Schematic representation of the simulated HPGe detector.
HPGe response function to Co-60 standard gamma-ray source was measured and compared with the simulated results to validate the simulated response function. Figure
A comparison between simulated and measured values at 1.173 MeV peak.
Energy | Simulated value | Measured value | Relative difference (%) |
---|---|---|---|
1173.58 | 0.58 | 0.59 | 1.6 |
1173.77 | 0.63 | 0.70 | 10.0 |
1173.97 | 0.78 | 0.81 | 3.0 |
1174.17 | 0.86 | 0.93 | 3.7 |
1174.36 | 1.00 | 1.00 | 0.0 |
1174.56 | 0.91 | 0.90 | 1.1 |
1174.76 | 0.73 | 0.79 | 6.0 |
1174.96 | 0.69 | 0.72 | 3.0 |
1175.15 | 0.65 | 0.63 | 3.1 |
Comparison between simulation and experimental gamma-ray spectrum of the Co-60 point source.
Detector’s simulation can provide powerful means to precisely determine detector’s response function, overcoming difficulties such as the unavailability of radiation sources with the required photon energies. This work has presented a way to simulate the response functions of HPGe by using GEB as a special treatment for tallies in MCNPX. Results show that MCNPX simulations by using GEB fit all the Gaussian peaks arising from standard gamma-ray sources in a wide range of energy with small discrepancies; typically Co-60 spectrum was shown. In this work based on our future works, the coefficients
The authors declare that there is no conflict of interests regarding the publication of this paper.