Coaxial HPGe Detector Research Articles

A novel method for computing the full-energy peak efficiency of coaxial high-purity germanium detectors for cylindrical sources

In this work a novel method for computing the full-energy peak efficiency of coaxial HPGe detectors for cylindrical sources emitting photons in the range of 60–2000 keV is described. It has a solid theoretical basis using an integral expression for computing the full-energy peak efficiency via computed values of the detector response and the attenuation factor of point sources. The method was implemented as a Matlab code written for computing the full-energy peak efficiency of a Canberra detector. The code was extensively verified by intercomparison with GESPECOR and LabSOCS codes and the results are fit purpose e.g. in the measurement of environmental samples.

Characterization and performance of co-axial HPGe detectors

Characterization and performance of co-axial HPGe detectors

Evaluation of Radioactivity Contents and Excess Lifetime Cancer Risk Due to Ingestion from Natural Radionuclides in Maize Samples from Some Selected Maize Farms in Ekiti State, Nigeria

The study was carried out to evaluate the radioactivity concentrations of 40K, 232Th and 238U in five maize samples collected from maize farms within Ekiti State, Nigeria. The activity concentration measurements were determined using n – type co-axial HPGe detectors for the state. The activity concentrations were found to vary from 994.67 – 2457.01 Bq Kg-1 for 40K, 32.84 – 91.88 Bq kg-1 for 232Th and 43.21 – 97.77 Bq kg-1 for 238U respectively. The annual effective dose to individuals from the consumption of the Maize was estimated on the basis of the measured radionuclides content in the food crop which ranged between 0.41 and 1.51 m Svy-1 respectively. The value1.04 m Svy-1 were obtained for the state as the mean total annual effective dose. The mean excess life time cancer risk was also calculated to be 2.06x10-9 . The value was compared with the internationally acceptable limits and found to be far less to the maximum permissible dose of 1.0 x10-3 recommended for the public by the United Nations Scientific Committee on the Effects of Atomic Radiation. Hence, the maize was found to be safe for human consumption.

Precision measurements of U3O8 and Ra(eU3O8) in uraniferous samples by gamma ray spectrometry using two HPGe coaxial P-type detectors (GCD30180 & GC5019 models)-a comparative study.

The precision measurements of U3O8 and Ra(eU3O8) concentrations were evaluated in 23 geological rock samples by high resolution gamma ray spectrometry (HPGe) using two P-type HPGe detectors. The use of Detector 2 (DET2) (GC5019) has increased the sensitivity by a factor of two for both the measurements in comparison to Detector 1 (DET1) (GCD30180). The Minimum Detection Limit (MDL) and Limit of quantification (LOQ) for U3O8 in DET2 has increased significantly because of negligible background counts in 1.001MeV ϒ energy peak (0.838% gamma yield). The MDL for Ra(eU3O8) measured by 0.609MeV and 1.760MeV has not improved significantly due to the high background counts in these energies whereas LOQ has improved appreciably. DET 2 has given higher level of confidence in reporting the analytical results with acceptable repeatability due to the decrease in uncertainty of the measurements.

The effects of the dead layer thickness increase to the regions in the spectrum response for a coaxial HPGe detector

The effects of the dead layer thickness increase to the regions in the spectrum response for a coaxial HPGe detector

Computational characterization of coaxial HPGe detectors using Monte Carlo simulation and nonlinear least squares optimization

Computational characterization of coaxial HPGe detectors using Monte Carlo simulation and nonlinear least squares optimization

Calibrating GESPECOR model of computing the full-energy peak efficiency of coaxial high-purity germanium detectors by Monte Carlo simulation

In this work, a classical approach was used for calibrating the GESPECOR detector model for computing the full-energy peak efficiency of p-type coaxial HPGe detectors that is based on the use of linear least squares optimization. The key element of the work is the multiplicative model developed for approximating the values of the full-energy peak efficiency provided by GESPECOR code. It was linearized using the logarithmic transformation to allow an easy use of the linear least squares optimization. A procedure was also developed to estimate the optimal values of the parameters, describing the p-type coaxial HPGe detectors. Its application to a Canberra detector GC3018 showed that it is possible to determine accurate values of the full-energy peak efficiency computed by GESPECOR code using the optimized parameter values.

Design and optimization of thermal neutron activation device based on 5 MeV electron linear accelerator

The optimized design of a Neutron Activation Analysis (NAA) system, including Delayed Gamma NAA (DGNAA) and Prompt Gamma NAA (PGNAA), has been proposed in this research based on Mevex Linac with 5 MeV electron energy and 50 kW power as a neutron source. Based on the MCNPX 2.6 simulation, the optimized configuration contains; tungsten as an electron-photon converter, BeO as a photoneutron target, BeD2 and plexiglass as moderators, and graphite as a reflector and collimator, as well as lead as a gamma shield. The obtained thermal neutron flux at the beam port is equal to 2.06×109(#/cm2.s).In addition, using the optimized neutron beam, the detection limit has been calculated for some elements such as H-1, B-10, Na-23, Al-27, and Ti-48. The HPGe Coaxial detector has been used to measure gamma rays emitted by nuclides in the sample. By the results, the proposed system can be an appropriate solution to measure the concentration and toxicity of elements in different samples such as food, soil, and plant samples.

Pulse shape discrimination and spectral performance of an inverted coaxial point contact HPGe detector with sub-pF capacitance

The inverted coaxial point contact high purity germanium (ICPC HPGe) detector exhibits the advantages of large volume, low depletion voltage, small capacitance, and excellent pulse shape discrimination (PSD) capability. An ICPC detector prototype with 0.9 pF capacitance was successfully fabricated and tested in this study using two different front-end electronics. The detector weighted approximately 1.5 kg and the depletion voltage was only 1800 V. The optimized operating voltage was found to be 2500 V and the leakage current was 7 pA. The detector was first connected to a homemade JFET based front-end with a pulsed reset design to minimize parallel noise. An energy resolution of 1.72 keV (full width at half maximum) was achieved at 1332 keV, demonstrating the good charge collection efficiency of the detector. An RC feedback front-end circuit was employed to test the PSD properties using a 228Th source. The PSD capability is similar to that of typical broad energy or point contact HPGe detectors, but is notably improved when the charge trapping is corrected using the drift time.

Utilization of different radionuclides for high-energy extended efficiency calibration of a HPGe for improved determination of calcium and sulfur using k0-INAA

The present study reports on the performance of three reactor-produced radionuclides (24Na, 56Mn, and 72Ga) and one accelerator-produced radionuclide (56Co) for extending the full-energy peak efficiency calibration of a coaxial HPGe detector up to ~ 3100 keV at different detector to source distances. The differences between the efficiency curves obtained with and without the use of high-energy gamma emitters radionuclides have a considerable impact on the accuracy of the Na, Ca, and S determination by the k0-INAA as evidenced by analysis results of reference materials. The results revealed that 24Na is the most suitable radionuclide for high-energy efficiency calibration due to its reasonable availability, low production cost, simple decay scheme, and well-defined decay properties.

Evaluating coincidence summing factor using marinelli beaker on coaxial HPGe detector by Monte Carlo simulation and calculating

This investigation aims to compare the full energy peak efficiencies in the energy range of 46-1836 keV on a type-p coaxial HPGe and estimate the coincidence summing factor for the case of Marinelli Beaker samples used by two general Monte-Carlo simulation software MCNP and PENELOPE. The radioactive nuclides used in determining the coincidence summing factor include 22Na, 60Co, 88Y, 133Ba, 134Cs, 154Eu, and 208Tl, which are prepared in HCl 2M solution and contained in a Marinelli beaker with the source’s volume of 3000 ml. The results demonstrate there is a good agreement between the two simulation software with an average discrepancy of 1.3%. On the other hand, the simulation coincidence summing factor values are also compared with the results from the calculating software ETNA with an average discrepancy of approximately 3.1%.

Development of a GAGG(Ce)-based compact 3D scanning setup for assessment of active volume in [formula omitted]-ray detectors

A Ce-doped GAGG (Gadolinium Aluminum Gallium Garnet: Gd3Al2Ga3O12) scintillator crystal has been coupled with a multianode position sensitive photomultiplier tube (PSPMT). The system is made compact by employing an external resistive network that reduces the 64 readouts of the PSPMT to only four signals. The resulting GAGG(Ce)-PSPMT setup has been put to use for quick scanning of γ-ray detectors by reconstructing the image of the latter with coincident photons between the pair of detectors. In the present work, such scans are demonstrated for an old single-crystal coaxial reverse-electrode HPGe detector as well as an old clover HPGe detector. For the single-crystal HPGe, the growth of the effective depleted region under increasing reverse-bias voltages has been visualized from the image reconstruction. The active volume is seen to grow from the surface towards the axial cavity. For the clover HPGe detector, dysfunctional portions in the crystals could be identified. The experimental results are found to agree well with simulation carried out using the GEANT4 toolkit. Scanning a detector using this method is faster compared to the scanning process by a point source.

Corrections of HPGe detector efficiency curve due to true coincidence summing by program EFFTRAN and by Monte Carlo simulations

Standard reference sources, used for efficiency curve calibration of detector, often contain radionuclides with complex decay schemes (such as 60Co, 88Y, 152Eu …), introducing a potential problem in gamma-ray spectrometry, due to the appearance of coincidence summing of detected photons, in particular at a low source-detector distance. In this paper, a set of Monte Carlo simulations of an identical experimental setup were performed in order to obtain the efficiency curve of coaxial p-type HPGe detector for energy region (0–2) MeV, with the effect of true coincidence summing and without it. Obtained efficiency curves are compared with the experimental curve after applied EFFTRAN corrections. Fairly well agreement (between simulated and experimental curves with EFFTRAN corrections (with a relative deviation of 10%) proved the reliability of EFFTRAN corrections, as well as the possibility of Monte Carlo simulations for efficiency curve determination.

Estimation of Fano factor for oversquare HPGe detector

Fano factor is a quantity used to measure the departure of the observed variance in the number of charge carriers produced from that predicted using poison statistics. Fano factor varies with the detector type. In case of proportional counters and semiconductor detectors, it is substantially less than unity, whereas, for scintillator detectors, it would be unity. Even in case of semiconductor detectors, it varies with the type and the shape of the detector. Another source of fluctuations that gives the overall resolution of the detector is preamplifier noise. Oversquare coaxial HPGe detectors are a recent development in the field. Literature on the Fano factor of oversquare large volume coaxial detector is not available. In this work, the Fano factor and the electronic noise of an oversquare HPGe coaxial detector are estimated after optimizing the shaping parameters. The Fano factor for the oversquare HPGe detector is estimated as 0.1291 keV, which agrees with the ideal value of 0.13 by 99.98%. The preamplifier noise was found to be 0.048 keV which is 35% lesser than the reported value.

Gamma-ray imaging performance of the GRI+ Compton camera

GRI+ (Gamma-Ray Imager) is a cart-based Compton camera developed at the University of Liverpool. The system comprises three electrically-cooled semiconductor detectors; two planar double-sided strip detectors (Si(Li) and HPGe) and an HPGe coaxial detector. The mobile cart houses the necessary components for data acquisition and analysis, providing complete functionality for imaging gamma-ray sources in an industrial setting. This paper reports on the operation of the system and the methods used to improve intrinsic system performance. The processing chain for extracting information pertaining to gamma-ray interactions has been developed and the imaging performance is characterised using an analytical reconstruction code. The obtainable Angular Resolution Measure (ARM) from a Cs-137 point source placed 10.5 cm from the front of the Si(Li) cryostat was determined to be 4.12∘ after the application of data processing techniques. The system energy resolution, which is key to isotope identification and image quality, was calculated to be less than 0.5% at 1332.5 keV.

Optimization of the n-type HPGe detector parameters using the “design of experiments” technique

This paper presents a new procedure to optimize the geometric parameters of a n-type coaxial HPGe detector. It is based on a statistical technique called “Design of Experiments” (DoE). This technique aims to identify the most influential parameters and to determine the optimal configuration. In this work, The effects of each parameter on the detector responses have been investigated by a fractional factorial design. Only the most influential factors contributing to the detector response have been selected. Precise modeling of these factors was then performed using a full factorial design. Based on the results obtained from this design, the full energy peak efficiencies according to the geometric parameters were modeled by a multiple-linear regression. These models have been statistically validated by analysis of variance (ANOVA). The optimal combination of the geometric parameters has been identified using the desirability function approach, which is a useful tool to optimize multi-response problems. A verification test was performed to validate the results obtained. It was observed that the relative deviation found between experimental and simulated values was less than 5%.

Validation of TOPAS MC for modelling the efficiency of an extended-range coaxial p-type HPGe detector

TOPAS MC software was used to model the efficiency of a coaxial p-type HPGe detector, type GX9023 from Canberra. The model was validated by comparing experimental efficiencies with efficiencies calculated by TOPAS MC simulations. Three different geometries of radionuclide sources, placed at different heights from the detector endcap, were used to validate the model. The imposed criteria of 5% relative difference was met for a range of radionuclides and gamma-ray energies. As a result, the created detector model with TOPAS MC was considered validated.

Measurement and simulation of gamma-ray background in a low energy accelerator facility

The γ-ray background in the indoor environment has been measured up to 3 MeV to evaluate the feasibility of studying low cross-section (nanobarn to picobarn range) astrophysical reactions at the Facility for Research in Experimental Nuclear Astrophysics (FRENA), Saha Institute of Nuclear Physics, Kolkata. An n-type coaxial HPGe detector with 20% relative efficiency has been placed at different locations in the accelerator and beam halls for the measurement. The measured activity has been compared with that at two laboratories (with standard brick walls) with and without passive and active radiation shieldings. As the halls at FRENA are well shielded by concrete, the contribution of the shielding in indoor γ-ray background has been delineated by simulation using a 4π-geometry model.

Uncertainties of calculated coincidence-summing correction factors in gamma-ray spectrometry

Uncertainty propagation to the γ-γ coincidence-summing correction factor from the covariances of the nuclear data and detection efficiencies have been formulated. The method was applied in the uncertainty analysis of the coincidence-summing correction factors in the γ-ray spectrometry of the 134Cs point source using a p-type coaxial HPGe detector.

Investigating the practicality of a minimally defined co-axial HPGe detector model using MCNP

An MCNP model of a co-axial HPGe detector, defined by the specification sheet and without parameter optimization, was used to assess practicality for efficiency characterization and complex spectra simulation. Simulated efficiencies, with and without Gaussian energy broadening, were compared against an experimental calibration for a standard counting geometry. Results show that this minimal detector model predicted efficiencies within 6% of experimental values at energies above 100 keV, while including energy broadening offered little improvement. This work shows that extensive detector characterization and optimization of parameters is not absolutely necessary, thereby reducing the experimental burden associated with detector modeling for many applications.