Broad Energy Germanium Detector Research Articles

Precision measurement of radioactivity in gamma-rays spectrometry using two HPGe detectors (BEGe-6530 and GC0818-7600SL models) comparison techniques: Application to the soil measurement

To obtain high quality of results in gamma spectrometry, it is necessary to select the best HPGe detector for particular measurements, to calibrate energy and efficiency of gamma detector as accurate as possible. To achieve this aim, the convenient detector model and gamma source can be very useful. The purpose of this study was to evaluate the soil specific activity using two HPGe model (BEGe-6530 and GC0818-7600SL) by comparing the results of the two detectors and the technics used according to the detector type. The relative uncertainty activity concentration was calculated for 226Ra, 232Th and 40K. For broad energy germanium detector, BEGe-6530, the relative uncertainty concentration ranged from 2.85 to 3.09% with a mean of 2.99% for 226Ra, from 2.29 to 2.49% with a means of 2.36% for 232Th and from 3.47 to 22.37% with a mean of 12.52% for 40K. For GC0818-7600SL detector, it was ranged from 10.45 to 25.55% with a mean of 17.10% for 226Ra, from 2.54 to 3.56% with a means of 3.10% for 232Th and from 3.42 to 7.65% with a mean of 5.58% for 40K. The average report between GC0818-7600SL model and BEGe-6530 model was calculated and showed the mean value of 3.36. The main study was based on the following points:•Determination of The relative uncertainty activity concentration of 226Ra, 232Th and 40K•Determination of the relative uncertainty related to the radium equivalent activity to compare the performance of the two detection systems•Proved that the activity concentration determination in gamma spectrometry depended on the energy range emitted by a radionuclide.This study showed that the standard deviation measurement was less important to the result realized with BEGe-6530 HPGe model. Our findings were demonstrated that the results of the Broad Energy Germanium detector were more reliable.

Characterization of a broad-energy germanium detector for its use in CJPL

The broad-energy germanium (BEGe) detector, with the ability of background discrimination using pulse shape discrimination, is a competitive candidate for neutrinoless double beta decay (0νββ) experiments. In this paper, we report our measurements of key parameters for detector modeling in a commercial p-type BEGe detector. Point-like sources are used to investigate energy resolution and linearity of the detector. A cylindrical volume source is used for efficiency calibration. With an assembled device for source positioning and a collimated 133Ba source, the detector is scanned to check its active volume. Using an 241Am point-like source, the dead layer thicknesses is measured at about 0.17 mm on the front and 1.18 mm on the side. The detector characterization is of importance for BEGe detectors to be used in the 0νββ experiments at China JinPing underground Laboratory (CJPL).

Determination of 226Ra, 232Th, 40K, 235U and 238U activity concentration and public dose assessment in soil samples from bauxite core deposits in Western Cameroon

Determination of activity concentrations in twenty five (25) soil samples collected from various points in bauxite ore deposit in Menoua Division in Western of Cameroon was done using gamma spectrometry based Broad Energy Germanium (BEGe6530) detector. The average terrestrial radionuclides of 40K, 226Ra, 232Th, 235U and 238U were measured as 671 ± 272, 125 ± 58, 157 ± 67, 6 ± 3 and 99 ± 69 Bq kg−1, respectively. The observed activity concentrations of radionuclides were compared with other published values in the world. The outdoor absorbed dose rate in air varied from 96.1 to 321.2 nGy h−1 with an average of 188.2 ± 59.4 nGy h−1. The external annual effective dose rate and external hazard index were estimated as 0.23 ± 0.07 mSv year−1 for outdoor, 0.92 ± 0.29 mSv year−1 for indoor and 1.13 for the external hazard index, respectively. These radiological safe parameters were relatively higher than the recommended safe limits of UNSCEAR. Consequently, using of soil as building material might lead to an increase the external exposure to natural radioactivity and future applications research need to be conducted to have a global view of radioactivity level in the area before any undergoing bauxite ore exploitation.

Determination of226Ra,232Th,40K and235U in soil samples from bauxite core deposits in western Cameroon

The activity concentrations of 226 Ra, 232 Th, 40 K and 235 U in soil samples from a bauxite ore deposit site in Western Cameroon were determined by gamma spectrometry using a Broad-Energy Germanium (BEGe6350) detector. The average activity concentrations of 226 Ra, 232 Th, 40 K and 235 U were found to be 124.8 ± 58.1, 157.3 ± 67.3, 670.9 ± 272.3 and 5.8 ± 2.7 Bq kg -1 , respectively. The measured activity concentrations of 226 Ra, 232 Th and 40 K were compared with available data in some countries and the world average activity concentration of soil. The radiological hazard indices of radioactivity were calculated, with average values of 416.90 Bq kg -1 for the radium equivalent activity, 188.20 nGy h -1 for the gamma radiation dose rate, 0.23 mSv y -1 for the external outdoor annual effective dose, 0.92 mSv y -1 for the indoor annual effective dose, 1.02 mSv y -1 for the total annual effective dose and 1.13 for the external hazard index, respectively. These radiological hazard index values were also compared with the internationally approved values. Consequently, use of concrete bricks made of soil as building materials might lead to an increased radiation risk for the population of Fongo-Tongo.

Modelling of Radiological Health Risks from Gold Mine Tailings in Wonderfonteinspruit Catchment Area, South Africa.

Mining is one of the major causes of elevation of naturally-occurring radionuclide material (NORM) concentrations on the Earth’s surface. The aim of this study was to evaluate the human risk associated with exposure to NORMs in soils from mine tailings around a gold mine. A broad-energy germanium detector was used to measure activity concentrations of these NORMs in 66 soil samples (56 from five mine tailings and 10 from the control area). The RESidual RADioactivity (RESRAD) OFFSITE modeling program (version 3.1) was then used to estimate the radiation doses and the cancer morbidity risk of uranium-238 (238U), thorium-232 (232Th), and potassium-40 (40K) for a hypothetical resident scenario. According to RESRAD prediction, the maximum total effective dose equivalent (TEDE) during 100 years was found to be 0.0315 mSv/year at year 30, while the maximum total excess cancer morbidity risk for all the pathways was 3.04 × 10−5 at year 15. The US Environmental Protection Agency considers acceptable for regulatory purposes a cancer risk in the range of 10−6 to 10−4. Therefore, results obtained from RESRAD OFFSITE code has shown that the health risk from gold mine tailings is within acceptable levels according to international standards.

Background rejection of n+ surface events in GERDA Phase II

The GERDA experiment searches for neutrinoless double beta (0vββ) decay in 76Ge using an array of high purity germanium (HPGe) detectors immersed in liquid argon (LAr). Phase II of the experiment uses 30 new broad energy germanium (BEGe) detectors with superior pulse shape discrimination capabilities compared to the previously used semi-coaxial detector design. By far the largest background component for BEGe detectors in GERDA are n+-surface events from 42K β decays which are intrinsic in LAr. The β particles with up to 3.5 MeV can traverse the 0.5 to 0.9 mm thick electrode and deposit energy within the region of interest for the 0vββ decay. However, those events have particular pulse shape features allowing for a strong discrimination. The understanding and simulation of this background, showing a reduction by up to a factor 145 with pulse shape discrimination alone, is presented in this work.

Optimized digital filtering techniques for radiation detection with HPGe detectors

This paper describes state-of-the-art digital filtering techniques that are part of GEANA, an automatic data analysis software used for the GERDA experiment. The discussed filters include a novel, nonlinear correction method for ballistic deficits, which is combined with one of three shaping filters: a pseudo-Gaussian, a modified trapezoidal, or a modified cusp filter. The performance of the filters is demonstrated with a 762g Broad Energy Germanium (BEGe) detector, produced by Canberra, that measures γ-ray lines from radioactive sources in an energy range between 59.5 and 2614.5keV. At 1332.5keV, together with the ballistic deficit correction method, all filters produce a comparable energy resolution of ~1.61keV FWHM. This value is superior to those measured by the manufacturer and those found in publications with detectors of a similar design and mass. At 59.5keV, the modified cusp filter without a ballistic deficit correction produced the best result, with an energy resolution of 0.46keV. It is observed that the loss in resolution by using a constant shaping time over the entire energy range is small when using the ballistic deficit correction method.

Reducing uncertainties for short lived cumulative fission product yields

Uncertainties associated with short lived (half-lives less than 1 day) fission product yields listed in databases such as the National Nuclear Data Center’s ENDF/B-VII are large enough for certain isotopes to provide an opportunity for new precision measurements to offer significant uncertainty reductions. A series of experiments has begun where small samples of 235U are irradiated with a pulsed, fission neutron spectrum at the Nevada National Security Site and placed between two broad-energy germanium detectors. The amount of various isotopes present immediately following the irradiation can be determined given the total counts and the calibrated properties of the detector system. The uncertainty on the fission yields for multiple isotopes has been reduced by nearly an order of magnitude.

Optimization of cylindrical sample geometry in determining the radioactive activity of environmental soil samples by using a Broad Energy Germanium detector

This paper describes the optimization of the geometric parameters of cylindrical geometry to maximize the detection efficiency for given sample volumes with a BEGe detector. A Monte Carlo model was developed and the detector efficiencies were studied for different sample geometries. The optimal sample dimensions that maximize the detection efficiencies have been determined by changing the sample dimensions through consecutive studies. The results show that the maximal detection efficiency depends on the appropriate selection of sample dimensions for a given sample volume. For the cylindrical geometry, the maximal detection efficiency can be obtained with the average sample radius/sample height value of about 1.75 (1.61 ∼ 1.91) for the corresponding given sample volume ranging from 150 to 400 cm3. Further studies show that the optimal sample height for a fixed cylindrical radius strongly depends on the measuring photon energy, and simply increasing the sample height does not generate higher full-energy peak net count rate. At last, optimal sample dimensions for the cylindrical geometry are recommended for a given detector specification with different sample volumes and photon energies.

Production, characterization and operation of $$^{76}$$ 76 Ge enriched BEGe detectors in GERDA

The GERmanium Detector Array (GERDA) at the Gran Sasso Underground Laboratory (LNGS) searches for the neutrinoless double beta decay (0{\nu}{\beta}{\beta}) of $^{76}$Ge. Germanium detectors made of material with an enriched $^{76}$Ge fraction act simultaneously as sources and detectors for this decay. During Phase I of the experiment mainly refurbished semi-coaxial Ge detectors from former experiments were used. For the upcoming Phase II, 30 new $^{76}$Ge enriched detectors of broad energy germanium (BEGe)-type were produced. A subgroup of these detectors has already been deployed in GERDA during Phase I. The present paper reviews the complete production chain of these BEGe detectors including isotopic enrichment, purification, crystal growth and diode production. The efforts in optimizing the mass yield and in minimizing the exposure of the $^{76}$Ge enriched germanium to cosmic radiation during processing are described. Furthermore, characterization measurements in vacuum cryostats of the first subgroup of seven BEGe detectors and their long-term behavior in liquid argon are discussed. The detector performance fulfills the requirements needed for the physics goals of GERDA Phase~II.

Radiological Hazards in Soil from the Bauxite Deposits Sites in Dschang Region of Cameroon

This work evaluates the radiological health risk from NORM exposure in bauxite deposition sites of West Region in Cameroon. In-situ and laboratory measurements were performed using dose rate survey meter and Broad Energy Germanium (BEGe) detector. Radiometric analysis of 226Ra, 232Th and 40K in the soil samples from Fongo-Tongo and Mini-Matap were done with average activity concentration of 108.91 Bq/kg, 117.79 Bq/kg and 143.07 Bq/kg and, 113.15Bq/kg, 196.14 Bq/kg and zero were determined respectively. In-situ measurement of dose rate at 1 m above the ground and the annual effective dose values due to 226Ra, 232Th and 40K in 5 cm soil layer were determined using conversion factors by UNSCEAR. The average external hazard indexes in samples from Fongo-Tongo were 0.78 and 1.06 while the internal hazard indexes in samples from Mini-Matap were 1.07 and 1.37. Comparing these values with the worldwide values set by UNSCEAR we realized that avoidance of high exposure from gamma radiation due to NORM to the populace should be of concern.

Improvement of the GERDA Ge Detectors Energy Resolution by an Optimized Digital Signal Processing

GERDA is a new generation experiment searching for neutrinoless double beta decay of 76Ge, operating at INFN Gran Sasso Laboratories (LNGS) since 2010. Coaxial and Broad Energy Germanium (BEGe) Detectors have been operated in liquid argon (LAr) in GERDA Phase I. In the framework of the second GERDA experimental phase, both the contacting technique, the connection to and the location of the front end readout devices are novel compared to those previously adopted, and several tests have been performed.In this work, starting from considerations on the energy scale stability of the GERDA Phase I calibrations and physics data sets, an optimized pulse filtering method has been developed and applied to the Phase II pilot tests data sets, and to few GERDA Phase I data sets. In this contribution the detector performances in term of energy resolution and time stability are here presented.The improvement of the energy resolution, compared to standard Gaussian shaping adopted for Phase I data analysis, is discussed and related to the optimized noise filtering capability. The result is an energy resolution better than 0.1% at 2.6 MeV for the BEGe detectors operated in the Phase II pilot tests and an improvement of the energy resolution in LAr of about 8% achieved on the GERDA Phase I calibration runs, compared to previous analysis algorithms.

A Dark Matter Search with MALBEK

The Majorana Demonstrator is an array of natural and enriched high purity germanium detectors that will search for the neutrinoless double-beta decay of 76Ge and perform a search for weakly interacting massive particles (WIMPs) with masses below 10GeV. As part of the Majorana research and development efforts, we have deployed a modified, low-background broad energy germanium detector at the Kimballton Underground Research Facility. With its sub-keV energy threshold, this detector is sensitive to potential non-Standard Model physics, including interactions with WIMPs. We discuss the backgrounds present in the WIMP region of interest and explore the impact of slow surface event contamination when searching for a WIMP signal.

An experimental characterisation of a Broad Energy Germanium detector

The spectroscopic and charge collection performance of a BE2825 Broad Energy Germanium (BEGe) detector has been experimentally investigated. The efficiency and energy resolution of the detector have been measured as a function of energy and the noise contributions to the preamplifier signal have been determined. Collimated gamma-ray sources mounted on an automated 3-axis scanning table have been used to study the variation in preamplifier signal shape with gamma-ray interaction position in the detector, so that the position-dependent charge collection process could be characterised. A suite of experimental measurements have also been undertaken to investigate the performance of the detector as a function of bias voltage and we report on anomalous behaviour observed when the detector was operating close to the depletion voltage.

Gamma Emitting Radionuclides in Soils from Selected Areas in Douala-Bassa Zone, Littoral Region of Cameroon

A study of natural radioactivity levels in some composites of eighteen soil samples selected within Douala-Bassa zone of Littoral Region has been evaluated. The samples were analysed using gamma spectrometry based broad energy germanium detector (BEGe 6350). The activity profile of radionuclide shows low activity across the studied areas. The obtained mean values of 226Ra, 232Th, and 40K in the two campuses were 25.48 Bq/kg, 65.96 Bq/kg, and 39.14 Bq/kg for Campus 1 and 24.50 Bq/kg, 66.71 Bq/kg, and 28.19 Bq/kg for Campus 2, respectively. In terms of health analysis, some radiation health hazard parameters were calculated within the two campuses. The mean values of radium equivalent activity were 122.81 Bq/kg and 122.08 Bq/kg, absorbed dose rate in air was 99.13 nGy/h and 98.18 nGy/y, annual outdoor effective dose was 0.12 mSv/y and 0.12 mSv/y, and external health hazard index was 0.34 and 0.33 in Campus 1 and Campus 2, respectively. These health hazard parameters were seen to be below the safe limit of UNSCEAR 2000 except the absorbed dose rate in air and the annual outdoor effective doses which are relatively high compared to the values of 60 nGy/h and 0.07 mSv/y. These results reveal no significant radiological health hazards for inhabitance within the study areas.

238U, 235U, 137Cs and 133Xe in soils from two campuses in University of Douala—Cameroon

An evaluation of 238U, 235U, 137Cs and 133Xe in soils from two campuses in University of Douala—Cameroon using gamma spectroscopy based Broad Energy Germanium Detector (BEGe6530) has been performed. The mean activities in soils from Campuse 1 were 40.16±8.98Bq/kg for 238U, 3.39±0.33Bq/kg for 235U, 0.46±0.33Bq/kg for 137Cs and 0.14±0.16Bq/kg for 133Xe. In Campus 2, the mean activities in soils were 31.45±12.24Bq/kg, 3.02±1.00Bq/kg, 0.30±0.26Bq/kg and 0.35±0.24Bq/kg for 238U, 235U, 137Cs and 133Xe, respectively. Using the in situ survey meter, the mean values of the absorbed dose rate measured was 71.43nGy/h for Campus 1 and 62.72nGy/h for Campus 2. The evaluated average outdoor effective dose for Campus 1 and 2 were 87.60µSv/yr and 76.93µSv/yr, respectively. The overall results obtained in this work were generally low compared to that of UNSCEAR.

Monte Carlo simulation of the BEGe detector response function for in vivo measurements of 241Am in the skull

This paper reports on the procedure of the BEGe detector characterization for the Monte Carlo calibrations. A project is under way to improve the counting and operating capabilities of the Whole Body Counter (WBC) installed in SÚRO, v.v.i. (NRPI) Prague, Czech Republic. Possible emergency monitoring should mainly benefit from the rapid, safe and flexible operation of the WBC. The system of the WBC for the detection of low energy X and gamma radiation comprises four HPGe detectors intended for the routine, emergency, and research measurements of persons internally contaminated with low-energy photon emitters, mainly actinides. Among them, 241 Am is the main subject of interest. A precise detection efficiency calibration of the detector is required for the measurement of activity in individual organs and tissues. The use of physical phantoms in the calibrations is often supplemented with the application of voxel phantoms and a Monte Carlo technique that are used for the calculation of the detector response function and the full energy peak efficiency. Both experimental and computational approaches have been used for the calibration of the BEGe (Broad Energy Germanium) detector. In this paper, the process of the Monte Carlo simulation of the detector response function and the peak efficiency calculation is described. Results of the simulations are provided in the paper and discussed. • MC calibration of the BEGe detector for internal contamination measurement. • Description of the BEGe detector parameters for MC simulations. • Three voxel skull phantoms have been used for MC simulations. • Comparison of the experimental and simulated gamma ray spectra is provided. • Efficiency calibration of WBC for measurements of 241 Am in the human skull.

The active area shadow-shielding effect on detection efficiency of collimated broad energy germanium detectors

The ISOCS calibration, when utilized for a BEGe detector with a small angled collimator, produces inaccuracies of about 19% for gamma rays with energies greater than 0.4MeV. Such a discrepancy is caused by the collimator algorithms currently utilized in the ISOCS software which, originally developed for HPGe detectors, are less suited for BEGe detectors. ISOCS's errors are due to the different crystal configurations of broad energy detectors compared to coaxial detectors, i.e. to a different importance of the active area portion obscured by the collimator. This work proposes some solutions for the problem, either using the ISOCS software or implementing a stochastic calibration procedure. In particular, the present work considers a virtual collimator that, maintaining its angular aperture, is capable of continuously enlarging its bottom collimator's aperture cone radius, to expose growing active area portions. In such a way two goals may be achieved: the mathematical characterization of ISOCS’ errors and the minimization of observed errors by means of the stochastic calibration procedure.Different reference set-ups are considered in order to test source geometry effects, source materials and different detectors. In particular, a 220L drum, a 2m3 box filled with uniformly contaminated cellulose or PVC, and small BE3825 and large BE5030 Canberra detectors are considered. Detection efficiencies calculated by ISOCS software are compared against a completely stochastic MCNPX simulation procedure, that is unaffected by any algorithmic correction. MCNPX simulations demonstrate, when widening collimators’ cone but maintaining the angular aperture unchanged, that ISOCS and MCNPX difference percentage between efficiency data points reduces, depending on energy, by more than 50%. This happens as far as the shadow-shielded portion of detector's active area reduces.

GERDA: Recent results and future plans

The GERmanium Detector Array (GERDA) is an experiment designed to investigate the neutrinoless double beta decay (0νββ) in 76Ge. An array of high purity germanium detectors isotopically enriched to 87% of 76Ge is operated within 64m3 of liquid argon (LAr) at the Laboratori Nazionali del Gran Sasso (LNGS). The experiment aims to explore the 0νββ half-life up to 1.4×1026yr with a collected exposure of 100kgyr separated into two physics phases. The data taking of Phase I started in November 2011 and finished in May 2013 with 21.6kgyr of exposure and a background index (BI) of 2×10−2cts/(kgyrkeV) around the Q-value of 2039keV before pulse shape cuts. Phase II of the experiment is being prepared with additional 30 Broad Energy Germanium (BEGe) detectors and an instrumentation of the LAr, aiming at a BI reduction by a factor of 10 w.r. to Phase I. This paper will present the GERDA setup and the latest results of the experiment including a new measurement of the 2νββ spectrum of 76Ge and the decomposition of the background spectrum. The 0νββ analysis, finished in the meanwhile, will be briefly mentioned. Furthermore, the major improvements planned for Phase II will be discussed.

HEROICA: an underground facility for the fast screening of germanium detectors

HEROICA (Hades Experimental Research Of Intrinsic CrystalAppliances) is an infrastructure to characterize germanium detectorsand has been designed and constructed at the HADESUnderground Research Laboratory, located in Mol (Belgium).Thanks to the 223 m overburden of clay and sand,the muon flux is lowered by four orders of magnitude.This natural shield minimizes theexposure of radio-pure germanium material to cosmic radiationresulting in a significant suppression of cosmogenic activation in thegermanium detectors.The project has been strongly motivated by a special production of germaniumdetectors for the GERDA experiment. GERDA, currently collecting data at theLaboratori Nazionali del Gran Sasso of INFN,is searching for the neutrinolessdouble beta decay of 76Ge. In the near future, GERDA will increase itsmass and sensitivity by adding new Broad Energy Germanium (BEGe) detectors.The production of the BEGe detectors is done at Canberra inOlen (Belgium), located about 30 km from the underground test site.Therefore, HADES is used both for storage of the crystals over night, duringdiode production, and for the characterization measurements.A full quality control chain has been setup and tested on the firstseven prototype detectors delivered by the manufacturerat the beginning of 2012.The screening capabilities demonstratethat the installed setup fulfills a fast and complete set of measurementson the diodes and it can be seen as a general test facilityfor the fast screening of high purity germanium detectors.The results are of major importance for a future massive productionand characterization chain of germanium diodes foreseen for a possiblenext generation 1-tonne double beta decay experiment with 76Ge.