High-purity Ge Detector Research Articles

Electron impact ionization cross sections of highly charged open L-shell tungsten ions

L-shell electron-impact ionization (EII) cross sections for highly charged tungsten ions were measured at incident electron energies of 29.10 and 38.92 keV using the Shanghai-EBIT. Resolved x-rays from radiative recombination (RR) processes were recorded with a high-purity Ge detector in a static electron energy scanning mode. Absolute EII cross sections were obtained by normalizing to the theoretical RR cross sections. The experimental results were compared with the calculated results using the relativistic distorted-wave method implemented in the flexible atomic code and the relativistic Lotz semi-empirical equation. The measurements showed general agreement with the calculated results by two theoretical methods for Li- to N-like W ions. The experimental uncertainties are not sufficiently small to discern the two theoretical results. Furthermore, the influence of Breit interaction on the EII cross sections of open L-shell tungsten ions was studied, and the effect is small but non-negligible. The measured EII cross sections of open L-shell tungsten ions would contribute to fusion plasma studies.

Final Result of the Majorana Demonstrator’s Search for Neutrinoless Double- β Decay in Ge76

The Majorana Demonstrator searched for neutrinoless double-β decay (0νββ) of ^{76}Ge using modular arrays of high-purity Ge detectors operated in vacuum cryostats in a low-background shield. The arrays operated with up to 40.4kg of detectors (27.2kg enriched to ∼88% in ^{76}Ge). From these measurements, the Demonstrator has accumulated 64.5kg yr of enriched active exposure. With a world-leading energy resolution of 2.52keV FWHM at the 2039keV Q_{ββ} (0.12%), we set a half-life limit of 0νββ in ^{76}Ge at T_{1/2}>8.3×10^{25} yr (90%C.L.). This provides a range of upper limits on m_{ββ} of (113-269)meV (90%C.L.), depending on the choice of nuclear matrix elements.

Gamma Radioactivity Detection Limits and Associated Radionuclide Intakes Study in Artificial Human Urine Using Sodium-iodide and High-purity Germanium Detectors.

The performance of several gamma detectors was investigated for emergency urine bioassay screening of two radionuclides of concern: 131 I and 137 Cs. Unspiked artificial urine samples were measured for 10 min each on four different gamma detectors: 80% relative efficiency high-purity Ge detector in standard shielding, 102% low-background high-purity Ge detector equipped with top muon shield, 78% high-purity Ge well detector in standard shielding, and 4″ × 4″ NaI well detector in standard shielding. The measured gamma spectra were analyzed in two ways: (1) for the 364-keV peak region of 131 I and 662-keV peak region of 137 Cs and (2) for the total counts in the full energy spectrum (50-2,048 keV). The results were analyzed using the principles of signal detection theory according to the Currie's formalism extended by a complete uncertainty propagation. This enabled calculation of the detection capability in terms of detection limit (Bq L -1 ) of urine, the latter referred to as minimum detectable activity. The NaI well detector had the lowest minimum detectable activities for total spectra, whereas the high-purity Ge well detector had the lowest peak minimum detectable activity values. Minimum detectable inhalation and ingestion intakes from urine bioassay were calculated from the minimum detectable activity values for urine collection 1 d, 1 wk, and 1 mo past the initial intake. The calculated intakes were compared with annual limits on intake. The results are interpreted with respect to a large-scale radiological emergency response.

Determination of natural radioactivity levels and radiation hazards for natural gypsum in Abay gorge, Dejen district, Ethiopia

ABSTRACT Natural gypsum has been studied as a building material, and it has been discovered that it is one of the potential sources of indoor radioactivity due to naturally occurring radioactive elements in it. The levels of radioactive elements obtained in natural gypsum available in Abay gorge Dejen district were accomplished by a well shielded and calibrated gamma spectrometry with high purity Ge detector to evaluate the radiation hazard to workers in Dejen gypsum factories and dwellers in buildings decorated with gypsum products. The results of this study revealed that radioactive elements 238U, 232Th, and 40K are found in raw gypsum samples, with specific activity ranging from 1.47 ± 0.26 to 2.42 ± 0.37 Bqkg−1, 1.10 ± 0.26 to 2.60 ± 0.48 Bqkg−1, and 4.27 ± 1.92 to 44.53 ± 2.84 Bqkg−1, respectively. The mean specific activities are 1.90 ± 0.33 Bqkg−1 for 238U, 1.99 ± 0.39 Bqkg−1 for 232Th, and 28.16 ± 2.57 Bqkg−1 for 40K, which are significantly lower than the intercontinental approved values. All of the calculated radioactive risk indices were significantly lower than the global recommended values for building materials. The values of various radioactive indices indicate that the use of gypsum powder obtained from studied samples in the construction of residences is considered safe.

SIMSPEC-G: a simple code for the simulation of HPGe detectors for gamma rays up to 1 MeV

A new program called SIMSPEC-G has been developed to simulate the interaction of gamma-rays of energies upto 1 MeV with different materials. In this work, 3 different geometries of high purity Ge (HPGe) detectors have been studied: single crystal HPGe, segmented single crystal HPGe and clover geometry composed of four HPGe crystals in clover-leaf arrangement. Contributions of different processes to peak formation have also been examined. The simulated spectrum, for a single crystal of clover, and for 662 keV gamma-ray (from 137Cs source) has been compared with experimentally obtained spectrum. The addback factor (gain in full energy peak efficiency due to the addition of the energies of the Compton scattered gamma rays in more than one crystal of a clover HPGe detector) and the hit pattern for a range of gamma-ray energies from the experiment have been excellently reproduced by the simulation leading to its validation. The fraction of total events in which highest or full energy is deposited in the first hit crystal is estimated and the use of this idea to improve angular resolution of a Clover detector has been explored.

Defining an equivalent geometry for Monte Carlo calculations of a high-purity Ge detector with high relative efficiency using a genetic algorithm

Detailed geometric information of a high-purity Ge (HPGe) detector is a very important issue for Monte Carlo simulation of the detector. Commonly, users have no geometric information about the detector and information given by the manufacturer is not completely valid for simulation. An equivalent geometry of detector, the parameters of which can be used for Monte Carlo simulation, is optimised using a genetic algorithm for a large-volume HPGe detector in this study. A mixed-point gamma calibration standard, emitting 12 useful gamma-radiation energies within 59.5–1836.1 keV, is placed at 74 different locations around the detector for this purpose. A high-quality solution is generated starting from an initial population of randomly-generated detector geometries using a genetic algorithm. Fitness of each geometry is obtained by comparing full energy peak efficiencies computed by Monte Carlo simulation with experimental values for each energy and position. Efficiencies with relative errors less than 5% for high energies and less than 7% for lower energies, except 59.5 keV, are obtained using optimised equivalent geometry parameters for the Monte Carlo simulation. Also, the necessity of using crystal dimensions smaller than real dimensions for Monte Carlo simulations of high-volume HPGe detectors is discussed. In addition, for Monte Carlo simulation of high-volume HPGe detectors, it is demonstrated that the use of smaller crystal dimensions than the real dimensions is necessary to obtain experimentally measured efficiencies of the detector.

Application of a mathematical model to an artificial aquifer under different recharge/discharge conditions using 222Rn as a tracer

Radon (222Rn), a radioactive gas of natural origin, was listed by the World Health Organization in 2009 as the second largest cause of lung cancer (3–14%) after tobacco. Global awareness of the importance of controlling its concentration in water led to the implementation of the European Directive 2013/51/Euratom, which establishes permitted levels in drinking water. This study applies a mathematical model to determine 222Rn concentration in water supplying an artificial aquifer over the full range of recharge/discharge conditions (volumes and times, and therefore flows). This was done by creating an artificial aquifer on a laboratory scale, which reproduces the recharges and discharges experienced by real aquifers through rainwater or groundwater. The equipment used in this study was an RTM 2100 with a specific system for continuous monitoring of 222Rn in water, a high-purity Ge detector for gamma spectrometry, and a portable liquid scintillation counter (LSC) called Triathler for specific measurements of 222Rn in water. The aim of this paper is to show the application of the mathematical model under different recharge/discharge conditions applied to the artificial aquifer. The concentration of 222Rn in water determined by the model can also be used as a tracer to find the origin and volume of water that reaches a real aquifer.

Source and LVis based coincidence summing correction in HPGe gamma-ray spectrometry

The activity of gamma-ray emitting nuclides is calculated assuming that each gamma-ray is detected individually; thus, the magnitude of the coincidence summing signal must be considered during activity calculations. Here, the correction factor for the coincidence summing effect was calculated, and the detection efficiencies of two HPGe detectors were compared. The CANBERRA Inc. GC4018 high-purity Ge detector provided an estimate for the peak-to-total ratio using a point source to determine the coincidence summing correction factor. The ORTEC Inc. GEM60 high-purity Ge detector uses EFFTRAN in LVis to obtain the parameters of the detector and source model and the gamma-gamma and gamma-X match estimates, in order to determine the coincidence summing correction factor. Nuclide analyses, radioactivity comparisons, and analyses of reference material samples were performed utilizing certified reference materials to accurately determine the detection efficiencies. For both Co-60 and Y-88, the detection efficiency for a point source increased by an average of at least 12–13%, whereas the detection efficiency determined using LVis increased by an average of at least 13–15%. The calculated radioactivity values of the certified reference material and reference material samples were accurate to within 3% and 6% of the measured values, respectively.

γ -ray emission in α -particle interactions with C, Mg, Si, and Fe at Eα=50–90 MeV

Nuclear deexcitation lines are regularly observed in the $\ensuremath{\gamma}$-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and $\ensuremath{\alpha}$ particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the $\ensuremath{\gamma}$-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the $\ensuremath{\gamma}$-ray emission in interactions of $\ensuremath{\alpha}$-particle beams of ${E}_{\ensuremath{\alpha}}=50\text{--}90$ MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one $\mathrm{La}{\mathrm{Br}}_{3}$:Ce detector have been employed to detect the $\ensuremath{\gamma}$ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt $\ensuremath{\gamma}$-ray emission from the targets from other $\ensuremath{\gamma}$ rays and neutron-induced background. $\ensuremath{\gamma}$-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, $^{12}\mathrm{C}$, $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$, $^{56}\mathrm{Fe}$, there are now measured cross-section data from reaction threshold to ${E}_{\ensuremath{\alpha}}=90$ MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong $\ensuremath{\gamma}$-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range.

A Study on the Improvement of Gamma Ray Energy Spectrum Resolution through Electrical Noise Reduction of High Purity Ge Detector

A Study on the Improvement of Gamma Ray Energy Spectrum Resolution through Electrical Noise Reduction of High Purity Ge Detector

Investigation of the electrical conduction mechanisms in P-type amorphous germanium electrical contacts for germanium detectors in searching for rare-event physics

For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of 2.13^{-0.05}_{+0.07}mathrm{{A}}^circ to 5.07^{-0.83}_{+2.58}mathrm{{A}}^circ , depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches.

Performance of in situ gamma-ray spectrometry in the assessment of radioactive cesium deposition around the Fukushima Daiichi nuclear power plant

In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with various dose rate levels around the Fukushima Daiichi nuclear power plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr3(Ce) detectors to assess the radioactive cesium deposition in the ground. Laboratory analysis of soil samples taken by depth from the sites was performed to evaluate the depth profile of radioactive cesium. The diverse levels of radioactivity of 137Cs were then distributed to six survey sites from 30 to 3000 kBq·m−2 in the measurement period of October 2018. Finally, a method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site. Except for the sites with relatively high lateral inhomogeneity of radioactive cesium, about 30% difference between two depth profiling methods using samples and in situ measurement was shown in the calculated radioactivity of 134Cs and 137Cs in the ground.

Natural Radioactivity Levels and Estimation of Radiation Exposure in Agricultural Soils from Skopje City Region

The aim of this study was to determine the activity concentrations of naturally occurring radioisotopes 226Ra, 232Th and 40K in 14 soil samples collected in the Skopje city surrounding, and to calculate the corresponding absorbed gamma dose rates. The radionuclides were measured applying a high purity Ge detector gamma-ray spectrometer with relative efficiency of 30 % at 1.33 MeV. The activity concentrations found in 14 soil samples varied in the range 24.1-41.9 Bq kg-1for 226Ra, 38.5-52.2 Bq kg-1 for 232Th, and 502-707 Bq kg-1 for40K. The mean radium equivalent (Raeq), for the area under investigation, was 143±16 Bq kg-1, while the outdoor radiation hazard index (Hex) was 0.39. The total absorbed dose rate due to three primordial radionuclides investigated lay in the range 55.3 - 79.0 nGy h-1 with mean value of 68.1±7.7 nGy h-1, yielding a total annual effective dose of (83.5±9.5) µSv y-1. The assessed radiological factors were lower than the recommended values, indicating low radiological health risk for the population living and working in the investigated area. The activity concentrations of radionuclides in soil samples were compared to the international values reported by United Nations Scientific Committee on the Effects of Atomic Radiation and previous studies on geographically close areas and some worldwide regions.

Adhesion-free Bridgman growth of AlSb

AlSb crystals as a dual-carrier compound semiconductor have a great potential application for the room-temperature detectors, comparative to high-purity Ge and CdZnTe detectors. However, the single crystal growth of AlSb suffers from the high reactivity of Al, which causes strong adheres of the crystal to the crucible walls. In this work, an in-situ synthesis method was developed using a pBN crucible sealed in a quartz crucible. Meanwhile, the reaction of Al and Sb was settled under the melting point with two stages for solid reaction and liquid reaction in turn. The cycles of rapid directional solidification and refusion were implemented for homogenization. Bulk crystals of AlSb with large grain size 5 × 5 mm2 were obtained from the vertical Bridgman method. The results of the XRD and EDS test showed a single zinc blende structure phase with a nearly stoichiometric atomic ratio of 49.7: 50.3 (Al: Sb). AlN was observed between AlSb/BN interface during the crystals with normal overheating synthesis. The sticking mechanism was ascribed to the increase of the adhesion energy with PBN crucible after the production of AlN. The chemical reactivity of Al has been fully inhibited during the Bridgman growth of AlSb.

Dielectronic resonances of and series in highly charged -shell tungsten ions.

We present spectroscopic measurements and detailed theoretical analysis of inner-shell and dielectronic resonances in highly charged -shell ions of tungsten. The x-ray emission from through was recorded at the electron-beam ion trap (EBIT) facility at the National Institute of Standards and Technology with a high-purity Ge detector for electron-beam energies between 6.8 and 10.8 keV. The measured spectra clearly show the presence of strong resonance features as well as direct excitation spectral lines. The analysis of the recorded spectra with large-scale collisional-radiative modeling of the EBIT plasma allowed us to unambiguously identify numerous dielectronic resonances associated with excitations of the inner-shell , , and electrons.

A multi-stop time-of-flight spectrometer for the measurement of positron annihilation-induced electrons in coincidence with the Doppler-shifted annihilation gamma photon.

In this study, we describe an advanced multi-functional, variable-energy positron beam system capable of measuring the energies of multiple "positron-induced" electrons in coincidence with the Doppler-shifted gamma photon resulting from the annihilation of the correlated positron. The measurements were carried out using the unique characteristics of the digital time-of-flight spectrometer and the gamma spectrometer available with the advanced positron beam system. These measurements have resulted in (i) the first digital time-of-flight spectrum of positron annihilation-induced Auger electrons generated using coincident signals from a high-purity Ge detector and a micro-channel plate, (ii) a two-dimensional array of the energy of Doppler-broadened annihilation gamma and the time-of-flight of positron-annihilation induced Auger electrons/secondary electrons measured in coincidence with the annihilation gamma photon, and (iii) the time-of-flight spectra of multiple secondary electrons ejected from a bilayer graphene surface as a result of the impact and/or annihilation of positrons. The novelty of the gamma-electron coincidence spectroscopy has been demonstrated by extracting the Doppler-broadened spectrum of gamma photons emitted due to the annihilation of positrons exclusively with 1s electrons of carbon. The width of the extracted Doppler-broadened gamma spectrum has been found to be consistent with the expected broadening of the annihilation gamma spectrum due to the momentum of the 1s electrons in carbon.

ADVANCES IN EXPERIMENTAL TECHNOLOGY BY THE EUROGAM DETECTOR SYSTEM

For the high resolution gamma ray detector array EUROGAM new data acquisition solutions are being developed. Large volume high purity Ge detectors, with new shapes for increased efficiency, have been proposed and prototypes are now being tested. High resolution analog and digital electronics will be integrated within the VXIbus system to be used as the front end instrumentation bus. Also, distributed processing solutions are adopted in order to cope with the high data rates.

Initial results from the Majorana Demonstrator

The Majorana Collaboration has assembled an array of high purity Ge detectors to search for neutrinoless double-beta decay in 76Ge with the goal of establishing the required background and scalability of a Ge-based next-generation ton-scale experiment. The Majorana Demonstrator consists of 44 kg of high-purity Ge (HPGe) detectors (30 kg enriched in 76Ge) with a low-noise p-type point contact (PPC) geometry. The detectors are split between two modules which are contained in a single lead and high-purity copper shield at the Sanford Underground Research Facility in Lead, South Dakota. Following a commissioning run that started in June 2015, the full detector array has been acquiring data since August 2016. We will discuss the status of the Majorana Demonstrator and initial results from the first physics run; including current background estimates, exotic low-energy physics searches, projections on the physics reach of the Demonstrator, and implications for a ton-scale Ge-based neutrinoless double-beta decay search.

Dispersion of 137Cs concentration in the basins of the Aegean Sea

The anthropogenic radionuclide 137Cs is used as a valuable oceanographic tracer for the study of sea water masses identification and water movement. In the present work, 137Cs activity concentrations have been investigated in deep basins of Aegean Sea. Seawater samples were collected from five different sampling stations, during scientific oceanic campaigns from the period March to April 2008. The applied methodology was based on the adsorption of radiocaesium from dissolved AMP (Ammonium Phosphomolybdate Hydrate) in 20 L water samples. Moreover, during the pre- concentration procedure, the 134Cs was used as reference tracer for determining the chemical efficiency and consequently to measure the activity concentration in a High Purity Ge detector. In terms of vertical records, the activity concentration in the selected basins ranged between 3-8.5 Bq/m3, depending on the region and the depth of the basins. The higher concentration (8.5 Bq/m3) was found in the region between Lemnos Island and the narrows of Dardanelles. The maximum concentrations were observed at the North Aegean Sea basins, between 20 and 40 m of depth, caused by the water masses coming from the Black Sea. At the Cretan Sea the vertical activity concentration of 137Cs was homogeneous down to 2000 m depth, with an exception at the 800 m where it was decreasing significantly due to the transient deep-water masses from Adriatic Sea.

Progress Toward A 2νββ Measurement For The Majorana Demonstrator

The MAJORANA DEMONSTRATOR is a 76Ge-based neutrinoless double-beta decay (0νββ) experiment. Staged at the 4850 ft level of the Sanford Underground Research Facility, the DEMONSTRATOR operates an array of high-purity p-type point contact Ge detectors deployed within a graded passive shield and an active muon veto system. The present work concerns the two-neutrino double-beta decay mode (2νββ) of 76Ge. For Ge detectors, having superior energy resolution (0.1%), this mode poses negligible background to the 0νββ mode, even for a ton-scale experiment. However, the measurement of the 2νββ mode allows for careful systematics checks of active detector mass, enrichment fraction, and pulse shape discrimination cuts related to both the 0νββ and 2νββ decay modes. A precision measurement of the 2νββ shape also allows searches for spectral distortions, possibly indicative of new physics, including 0νββχ. Work is underway to construct a full experimental background model enabling a Bayesian fit to the measured energy spectrum and extraction of a precise 2νββ spectrum and half-life.