P-type High Purity Germanium Research Articles

Pulse shape discrimination for the CONUS experiment in the keV and sub-keV regime

Point-contact p-type high-purity germanium detectors (PPC HPGe) are particularly suited for detection of sub-keV nuclear recoils from coherent elastic scattering of neutrinos or light dark matter particles. While these particles are expected to interact homogeneously in the entire detector volume, specific classes of external background radiation preferably deposit their energy close to the semi-active detector surface, in which diffusion processes dominate that subsequently lead to slower rising pulses compared to the ones from the fully active bulk volume. Dedicated studies of their shape are therefore highly beneficial for the understanding and the rejection of these unwanted events. This article reports about the development of a data-driven pulse shape discrimination (PSD) method for the four 1 kg size PPC HPGe detectors of the Conus experiment in the keV and sub-keV regime down to 210 eVee.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{ee}.$$\\end{document} The impact of the electronic noise at such low energies is carefully examined. It is shown that for an acceptance of 90% of the faster signal-like pulses from the bulk volume, approx. 50% of the surface events can be rejected at the energy threshold and that their contribution is fully suppressed above 800 eVee.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{ee}.$$\\end{document} Applied to the Conus background data, such a PSD rejection cut allows to achieve an overall (15-25)%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(15{-}25)\\%$$\\end{document} reduction of the total background budget. The new method allows to improve the sensitivity of future Conus analyses and to refine the corresponding background model in the sub-keV energy region.

Modeling the charge collection efficiency in the Li-diffused inactive layer of P-type high purity germanium detector

A model of the Li-diffused inactive layer in P-type high purity germanium detectors is built to describe the transportation of charge carriers and calculate the charge collection efficiency therein. The model is applied to calculate charge collection efficiency of a P-type point-contact germanium detector used in rare event physics experiments and validated in another P-type semi-planar germanium detector. The calculated charge collection efficiency curves are well consistent with measurements for both detectors. Effects of the Li doping processes on the charge collection efficiency are discussed based on the model. This model can be easily extended to other P-type germanium detectors, for instance, the P-type broad-energy Ge detector, and the P-type inverted-coaxial point-contact detector.

Prototyping experience with Ge micro-strip sensors for EDXAS experiments

Energy dispersive X-ray spectrometers provide a method for the fast data acquisition of X-ray absorption spectra. The intensity of the spectral components of a polychromatic beam is detected simultaneously after being dispersed in space, and being transmitted by an experimental sample. The cryogenic detector system called XH deploys a germanium micro-strip sensor to perform such measurements. Here, the geometrical position of each strip is correlated to a specific spectral component of the dispersed beam.The prototyping experience reported in this work is related to the upgrade of the cryostat unit of the XH detector system. This upgrade was carried out in collaboration with beam-line ID24 at the European Synchrotron Radiation Facility (ESRF).Two 90 mm wafers of p-type high purity germanium were manufactured. Wafers contained test structures and micro-strip sensors made of 1024 strips with 50μm pitch. Electrical and in-beam tests were performed to verify the performance of this technology. The measurements included capacitance–voltage characteristics; stress-tests like temperature cycling testing and burn-in tests; leakage current as a function of sensor temperature; charge-collection as a function of time; a test-run of a pump and probe experiment.Results are reported below showing that this sensor technology survived the extensive thermal and electrical stress-tests, and that it was able to measure the physical variations created by a laser shock on a sample of Fe–10%wtNi.

Evaluation the nonlinear response function of a HPGe detector for 59 keV to 10.7 MeV gamma-rays using a Monte Carlo simulation and comparison with experimental data

Modeling of High Purity Germanium (HPGe) detector on a wide energy range is important in gamma-ray spectroscopy. The precisely modeled detector can be used for proton-induced prompt gamma-ray spectroscopy. In this work, we used both the gamma-rays of calibration sources and prompt gamma-rays emitted in proton capture reactions to model a coaxial p-type HPGe detector using Geant4 Monte Carlo simulation for the gamma-ray energy range of 59–10764 keV. The calibration sources were 137Cs, 241Am, 60Co, 152Eu, and 133Ba, while the prompt gamma-rays were due to the gamma-ray cascades following the 27Al(p,γ)28Si reaction capture at the resonant energies of 992, 1317 and 2483 keV, as well as the 23Na(p,γ)24Mg reaction capture at the resonant energies of 1417 and 1395 keV. According to the results obtained, the presented simulated and experimental spectra show a good agreement. In addition, the mean and maximum relative deviations between experimental and simulated efficiencies corresponding to 27 major peaks are smaller than 5% and 15%, respectively.

Segmented HPGe Detector for Nuclear Reactions Research

In this article, development results from a new p-type high-purity germanium (HPGe) detector with a segmented n+-region are presented. The intended detector is used in spectrometry; however, its sixfold segmentation allows for the determination of the direction of individual photons emitted in the nuclear reactions from a source placed inside the detector. The capacitance and current voltage characteristics of the detector are presented. At full depletion of −1500 V, the segments’ capacitance was measured to be 17 pF and leakage currents ranged between 7 and 10 pA. The energy resolution of the segments was measured with a variety of gamma sources and determined to be less than 1000 eV at 122 keV and less than 1900 eV at 1332 keV. The incident photon angle response from a radiation source placed inside the detector was also studied.

Radionuclide activity concentration in soil, granites and water in a fluorosis endemic area of India: An oral health perspective

BackgroundThe idea that hilly areas have a high background radiation which in turn is linked to dental fluorosis is widely held by many in India. There is little evidence to confirm this. ObjectiveThe study aimed to investigate the level of environmental radionuclide in order to determine any interrelationship between radionuclide and dental fluorosis in Pavagada, a fluorosis endemic area of Karnataka, India. MethodsGamma radionuclides (Th232, Ra226 and K40) were determined by high purity germanium (HPGe) gamma-ray spectrometer (Bq Kg-1) using a 50% relative efficiency p-type broad energy HPGe detector. Fluoride was estimated using fluoride Ion-selective electrode (ISE). Fluorosis was assessed using WHO diagnostic criteria. ResultsThe average mean +_SD activity concentration in soil for K40 was detected between 416.6 ± 9.3 and 769.1 ± 15.0. Th232 was estimated between 13.6 ± 0.6 and 57.6 ± 1.3; and Ra226 was found between 6.4 ± 0.4 and 21.6 ± 0.7. Similarly, the mean activity concentration detected (Bq kg-1) in granite for K40 ranged between 259.8 ± 6.9 and 1608.5 ± 26.9. The activity concentration of Th232 ranged between 26.4 ± 0.8 and 57.6 ± 1.3: and that of Ra226 was between 6.6 ± 0.3 and 21.6 ± 07. Drinking water contains 2.98 ppm of fluoride. Dental fluorosis was diagnosed as mild to moderate. ConclusionThe radionuclide activity in water, soil and granites were below the detection limit. Hence, the study revealed no association of fluorosis and radionuclide level in Pavagada, Karnataka, India. This helps resolve an ambiguity.

Radiation background from rock samples and hazards assessment: case of Mounana in Gabon

The aim in this present work is to determine the specific activities of 226Ra, 232Th and 40K in rock samples collected from Mounana in Gabon, to assess the contribution of natural radioactivity. A p-type high-purity germanium detector has been coupled with a multichannel analyser DSA-1000 to perform measurements and data processing. The energy resolution of the 1332 keV60Co line is still found to be 1.8 keV at FWHM, with a relative efficiency of 30%. The specific activities average values of 226Ra, 232Th and 40K are 6554±198 Bq/kg, 63±12 Bq/kg and 513±93 Bq/kg, respectively wet weight. To assess the radiological risks due to 226Ra, 232Th and 40K, many parameters were estimated. The average value of annual effective dose was 18.95 mSv from the studied area. Rock from Mounana presents a high radioactivity, and we are planning to measure radon in homes to assess the risks of living in Mounana.

Radiation background from rock samples and hazards assessment: case of Mounana in Gabon

The aim in this present work is to determine the specific activities of 226Ra, 232Th and 40K in rock samples collected from Mounana in Gabon, to assess the contribution of natural radioactivity. A p-type high-purity germanium detector has been coupled with a multichannel analyser DSA-1000 to perform measurements and data processing. The energy resolution of the 1332 keV60Co line is still found to be 1.8 keV at FWHM, with a relative efficiency of 30%. The specific activities average values of 226Ra, 232Th and 40K are 6554±198 Bq/kg, 63±12 Bq/kg and 513±93 Bq/kg, respectively wet weight. To assess the radiological risks due to 226Ra, 232Th and 40K, many parameters were estimated. The average value of annual effective dose was 18.95 mSv from the studied area. Rock from Mounana presents a high radioactivity, and we are planning to measure radon in homes to assess the risks of living in Mounana.

Classification of rocks radionuclide data using machine learning techniques

The aim of this study is to assess the performance of linear discriminate analysis, support vector machines (SVMs) with linear and radial basis, classification and regression trees and random forest (RF) in the classification of radionuclide data obtained from three different types of rocks. Radionuclide data were obtained for metamorphic, sedimentary and igneous rocks using gamma spectroscopic method. A P-type high-purity germanium detector was used for the radiometric study. For analysis purpose, we have determined activity concentrations of 232Th, 226Ra and 40K radionuclides, published elsewhere (Rafique et al. in Russ Geol Geophys 55:1073–1082, 2014), in different rock samples and built the classification model after pre-processing the data using three times tenfold cross-validation. Using this model, we have classified the new samples into known categories of sedimentary, igneous and metamorphic. The statistics depicts that RF and SVM with radial kernel outperform as compared to other classification methods in terms of error rate, area under the curve and with respect to other performance measures.

Experimental Investigation on the Photopeak Efficiency of a Coaxial High Purity Germanium Detector for Different Geometries

Purpose: Gamma spectrometer systems are complex instruments, and the quality of the numerical results they provide strongly depends on their reliable calibration. In this study, it was aimed to determine the full-energy peak efficiencies of a 40% p-type High Purity Germanium HPGe detector for point source, Marinelli beaker, and cylindrical container geometries in the 200-1500 keV energy range. Methods: The efficiency calibration of the HPGe gamma spectrometry system was performed using certified calibration sources. Efficiency values were determined using the gamma ray spectrum acquired for every calibration source.Results: Two different efficiency curves, at the linear scale and logarithmic scale-fitting, experimental efficiencies were plotted. The functions and parameters that fitted the efficiency curves were obtained by a computer program.Conclusion: The photopeak efficiencies decrease as energy increases and the observed efficiency curves were closely with similar studies

Ultra-low noise mechanically cooled germanium detector

Low capacitance, large volume, high purity germanium (HPGe) radiation detectors have been successfully employed in low-background physics experiments. However, some physical processes may not be detectable with existing detectors whose energy thresholds are limited by electronic noise. In this paper, methods are presented which can lower the electronic noise of these detectors. Through ultra-low vibration mechanical cooling and wire bonding of a CMOS charge sensitive preamplifier to a sub-pF p-type point contact HPGe detector, we demonstrate electronic noise levels below 40eV-FWHM.

Measurements of Natural Radionuclides in Vegetables by Gamma Spectrometry

This article reports the activity of natural radionuclides uranium, thorium, and potassium, in different vegetables in Malaysia, measured with a p-type high-purity germanium detector (HPGe). Potassium radionuclides were the most prevalent element in the tested samples, whose activity ranges from 138.89 to 2660.31 Bq/kg. Meanwhile, the activity of uranium was found to be within the minimum detection limit (MDL) to 46.94 Bq/kg, and thorium from < MDL to 192.98 Bq/kg. The annual dose was in the range 0.001 to 0.06 mSv, within the worldwide range of 0.29 mSv/year for ingestion of vegetables.

Effect of annealing on contact performance and electrical properties of p-type high purity germanium single crystal

Van de Pauw Hall measurement is an effective method to characterize the properties of semiconductors, such as bulk concentration, mobility, and resistivity, all of which are used to describe the purity level in the semiconductors. However, the performance of the ohmic contacts has a direct impact on the reliability and accuracy of the results obtained from the Van de Pauw Hall measurement. In the present work, the influences of different annealing techniques on the performance of the InSn ohmic contacts have been investigated using a High Purity Germanium (HPGe) crystal sample. The results show that the preferred annealing condition is at 400 °C for 1 hour, which has provided a significant improvement of the InSn contact quality and microscopic homogenization of the impurities in the HPGe crystal. The carrier concentration, charge mobility, and resistivity of the sample annealed at 400 °C for 1 hour are 5.772×1010/cm3, 1.883×104× cm2/Vs, and 5.795×103×Ω cm at 77 K, respectively.

Effect of a surface channel on the performance of a P-type Point Contact HPGe detector

The observation of anomalous charge collection in a P-type Point Contact (PPC) High Purity Germanium (HPGe) detector is reported. By studying preamplifier charge signals from the detector, these anomalous events are shown to be consistent with charge carrier drift along the surface of the detector, prior to collection at the contact. It is believed that these events arise from the formation of a surface channel in the detector. By coupling analysis of these experimental signals with field calculations, an estimate of the radial drift velocity of holes at the surface has been made. This value is found to be around 40 times slower than the accepted value for saturated hole drift in the bulk, and is in good agreement with that calculated using a newly developed technique for modelling carrier transport.

LArGe: Background suppression using liquid argon (LAr) scintillation for 0 νββ decay search with enriched germanium (Ge) detectors

Measurements with a bare p-type high purity germanium diode (HPGe) submerged in a 19 kg liquid argon (LAr) scintillation detector at MPIK-Heidelberg are reported. The liquid argon–germanium system (LArGe) is operated as a 4π anti-Compton spectrometer to suppress backgrounds in the HPGe. This R&D is carried out in the framework of the Gerda experiment which searches for 0νββ decays with HPGe detectors enriched in 76Ge. The goal of this work is to develop a novel method to discriminate backgrounds in 0νββ search which would ultimately allow to investigate the effective neutrino mass free of background events down to the inverse mass hierarchy scale. Other applications in low-background counting are expected.

An empirical function for the full energy peak efficiency for a P-type Co-axial high purity germanium detector

An empirical analytical function has been obtained for the full energy peak efficiency of a co-axial P-type High Purity Germanium Detector for gamma-ray energies in the range of 80 - 1333 keV and source-to-detector distance in the range of 1.0 - 4.0 cm. Comparison of the calculated efficiencies with the corresponding experimental value agrees very well within standard deviations of 1.8 - 3.7 %. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 1 (2000) pp. 64-70

The High Purity Germanium Detector Whole Body Monitor at PSI

For the in vivo monitoring of radiation workers a new measurement system has been installed at PSI, Switzerland. A single p-type high purity germanium detector of 102% relative efficiency is mounted in a shielded room located in a subterranean shelter. The room has internal dimensions of 270 cm × 190cm × 220 cm and is constructed of iron from old railway rails. The detector is mounted on a mechanical support fixed on the ceiling, which permits movements in three directions and two axes. Measurements of radionuclides in the body are performed in a sitting position. The system is used to detect the presence of radionuclides that emit photons with energies between 50 keV and 2 MeV. A description of the system is presented. The results of calibration of the detector for total-body activity measurements are discussed. The performances of the new system and the old Nal(TI) body monitor used at PSI are compared.

Optical deep level transient spectroscopy of minority carrier traps in n-type high-purity germanium

Deep levels in n-type high-purity (HP) detector grade germanium are studied using optical deep level transient spectroscopy (ODLTS). In this technique, optical injection (using light of above band gap energy) from the back ohmic contact together with a suitable sample configuration results in the detection of centers in the minority half of the band gap. Six deep minority carrier traps are detected in typical n-type HP germanium which turn out to be the same defects as found earlier in typical p-type HP germanium as majority carrier traps. These deep defects are mainly copper related. A formula is deduced to calculate concentrations from the ODLTS spectra. It is shown that in n- and p-type HP germanium not only the same defects are present but that their concentrations are also comparable.

Radiation damage in large-volume n- and p-type high-purity germanium detectors irradiated by 1.5 GeV protons

Excellent energy resolution makes germanium detectors prime candidates for gamma-ray spectroscopy in space missions. We present a study of several large-volume n-type and p-type high purity,germanium (HPGe) detectors that were damaged by 1.5 GeV protons and examine their performance as function of fluence, operating and anneal temperature, and time. n-type detectors exhibit essential advantages for space applications over p-type detectors. Annealing at about 110 K for both detector types was observed as well as resolution transients up to 134 K. We discuss the observed radiation effects with respect to existing models and show their limitations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Correlation between deep-level parameters and energy resolution of p-type high purity Ge γ-detectors

A physical basis is presented for the previously reported correlation between deep levels in p-type high purity germanium and the energy resolution of corresponding γ-detectors. Taking account of re-emission of trapped holes at 77 K it is shown that effective hole traps are deeper than about E v + 0.07 eV. Slowly re-emitting traps may become saturated during detector operation. The detector resolution criterion L ≤ 2 keV is found to correspond with an upper limit of 4.5 × 10 9 cm −3 for the total active copper density. This density criterion is shown to be a reliable basis for the routine DLTS characterisation of high purity germanium production.