Ge Detector Research Articles

Spectroscopic study of Mo97, Mo99 , and Mo101

Excited states of the molybdenum isotopes Mo4297,99,101 have been populated in two experiments which used fusion-fission and binary grazing reactions to populate yrast states of the nuclei of interest. In the first experiment, the GASP array of escape-suppressed Ge detectors was used to detect γ rays from fusion-fission products initiated by the interaction of a 230-MeV beam of S36 ions with a thick target of Yb176. In the multinucleon transfer experiment, a 530-MeV beam of Zr96 ions was incident on a thin Sn124 target; projectile-like ejectiles were detected and identified using the PRISMA magnetic spectrometer and their associated γ rays were detected using the CLARA array of escape-suppressed Ge detectors. In Mo99, the previously known positive-parity νd5/2 decay sequence was extended to spin (25/2+) while, in Mo101, a similar, but hitherto unobserved νg7/2 positive-parity decay sequence was established to spin (27/2+). In Mo99 and in Mo101, previously observed νh11/2 negative-parity decay sequences were also observed to spin 27/2−. Although the observed decay sequences in Mo97 have not been extended beyond the results of earlier work, a disagreement in the published level structure of the h11/2 band has been resolved. The observed positive-parity decay sequences have been compared with the results of state-of-the-art shell-model calculations; the general features of the energy spectrum of excited states of Mo97, Mo99, and Mo101 are reproduced, but not in detail. The experimental energies of the negative-parity states of Mo99 and Mo101 are reasonably well reproduced in particle-rotor (PRM) calculations. For Mo97, better agreement with the high-spin states was obtained when the core in the PRM calculations was treated in a variable moment of inertia approach. For the νh11/2 negative-parity decay sequences of the three isotopes studied here, model-dependent evidence is presented for nuclear shape changes with increasing neutron number. Published by the American Physical Society 2024

Testing for coherence and nonstandard neutrino interactions in COHERENT data

We analyze data from the CsI, liquid Ar and Ge detectors of the COHERENT experiment and confirm within 1.5σ that the measured elastic neutrino-nucleus scattering cross section is proportional to the square of the number of neutrons in the nucleus, as expected for coherent scattering in the standard model. We also show how various degeneracies involving nonstandard neutrino interaction parameters are broken in a combined analysis of the three datasets. Published by the American Physical Society 2024

Exploring charge transport dynamics in a cryogenic P-type germanium detector

This study explores the dynamics of charge transport within a cryogenic P-type Ge particle detector, fabricated from a crystal cultivated at the University of South Dakota. By subjecting the detector to cryogenic temperatures and an Am-241 source, we observe evolving charge dynamics and the emergence of cluster dipole states, leading to the impact ionization process at 40 mK. Our analysis focuses on crucial parameters: the zero-field cross-section of cluster dipole states and the binding energy of these states. For the Ge detector in our investigation, the zero-field cross-section of cluster dipole states is determined to be 8.45 × 10−11 ± 4.22 × 10−12 cm2. Examination of the binding energy associated with cluster dipole states, formed by charge trapping onto dipole states during the freeze-out process, reveals a value of 0.034 ± 0.0017 meV. These findings shed light on the intricate charge states influenced by the interplay of temperature and electric field, with potential implications for the sensitivity in detecting low-mass dark matter.

Calibration for in vivo monitoring of thyroid of exposed population at risk of intakes of radioiodine isotopes due to a nuclear or radiological emergency

This work presents an improvement of the calibration of a broad energy germanium detector (BEGe) using age dependent neck-thyroid phantoms for thyroid monitoring of exposed individuals (workers and members of the public), allowing the detection and quantification of incorporated radioiodine isotopes in a nuclear medicine frame or in case of accident of a nuclear reactor.A BEGe detector was calibrated using a family of age-dependent thyroid-neck phantoms that simulate thyroids of 1, 5, 10, 15 year-old children and (male and female) adults, based in ICRP Publication 8 (ICRP, 2002) and ANSI 13.44 Standard (ANSI, 2014).The calibration of the BEGe detector for all neck phantoms was performed with the same counting geometry, centered under the BE Ge detector and at the same distance of 15 cm. Using same counting parameters allows to compare efficiency curves of thyroid monitoring depending with age. The in vivo measurements with the BE Ge detector allow to identify X rays and gamma emissions between 10 and 1000 keV with a great resolution and to quantify activities of radioiodine isotopes in the thyroid of exposed population.Calibration curves have been obtained for different sizes of the thyroid, depending with age. This study of counting efficiency using the main energies of the most important radioiodine isotopes result in accurate activity calculations. Detection limits were obtained for each radioiodine isotope, using blank phantoms of each age.

Evaluation of lithium tetra borate glass-ceramics: Structural, physical and radiation safety properties using experimental and theoretical methods

By using the standard melt quenching method, samples of lithium borate glass-ceramics with a composition of 40Li2B4O7 + xLi2O +(50-x)NiO+5Gd2O3 + 5BaTiO3 (x = 10 (C1), 20 (C2), 30 (C3), 40 (C4) and 50 (C5) wt%) have been manufactured. The structural and physical characteristics of the prepared C1–C5 samples have been investigated. Using an Ultra Ge detector and a 133Ba (3 Ci) radioisotope source as well as theoretically using EpiXS software, the radiation shielding competence of the C1–C5 samples were examined. The XRD analysis showed large crystal particle sizes were formed in the C1 sample, where the amount of NiO in its structure was maximum and the amount of Li2O was minimum. The change in the NiO/Li2O ratio caused the crystal particle size in the structure to decrease. Additionally, it was observed that the particle size increased in the C4 structure. In addition, the C3 and C5 structures became completely amorphous. This doping in the structure caused the crystal structure of C3 and C5 to deteriorate. While increasing the amount of NiO in the structure gave positive results up to a certain value, increasing the Li2O structure disrupted the crystal structure. A range of 2.91–4.51 g/cm3 was observed in the density of the synthesized C1, C2, C3, C4, and C5 samples. The dense C1 sample proved to have the largest mass-attenuation coefficient (MAC). The results obtained from experiments agree with the theoretical ones. There are no differences in the trends of the MAC and linear attenuation (LAC) coefficient. For each given energy, the half-value layer (HVL) organized as (HVL)C5 > (HVL)C4 > (HVL)C3 > (HVL)C2 > (HVL)C1. Results revealed that glass-ceramics are one source of materials that can be used for radiation shielding.

Zenith angle dependence on cosmic-ray background in HPGe gamma spectrometers by using GEANT4 simulation

In this study, we investigate the impact of zenith angle variations on cosmic-ray induced background in High-Purity Germanium (HPGe) gamma spectrometers using a coincidence technique based on plastic scintillator-Germanium detectors. We utilize an HPGe detector (Model GC2018 Mirion Ge Detector) enclosed within a low-activity cylindrical lead shield (Model 747E Mirion Lead Shield). For cosmic ray detection, a coincidence detection system with plastic scintillator detectors was positioned on top of the lead shielding. The zenith angle at the Germanium detector is computed using the dimensions of the square plastic scintillator and its distance from the Germanium detector center. We carried out measurements of cosmic-ray induced background in an HPGe gamma spectrometer with a square plastic configuration (80cm x 80cm), equivalent to a 45° zenith angle. The experimental measurements were compared with GEANT4 simulation data. The results demonstrate a good agreement between the measured energy spectrum and the simulated data across the energy range of 0.05 to 47 MeV. Further investigations into the effects of varying zenith angles provide valuable insights for optimizing HPGe spectrometer setups with minimized background interference.

Impact of La2O3 incorporation on the structural, physical, mechanical properties and radiation shielding performance of basalt glasses

This study investigates the influence of La2O3 addition on the structural, physical, and radiation shielding properties of basalt-based glasses. Incorporating varying concentrations of La2O3 (0, 10, 20, 30 wt%) into basalt glasses, we aimed to evaluate the potential of La2O3 in enhancing the material's effectiveness against gamma radiation. Utilizing Ba-133 point radioactive source and Ultra Ge detector, we measured the attenuation parameters in different photon energies (81, 160, 223, 276, 302, 356, and 383 keV). The glasses exhibited an amorphous structure, as confirmed by XRD analysis, with density values ranging from 2.72 to 3.305 g/cm³, increasing with La2O3 content. The microstructural analysis indicated that La3+ ions predominantly integrate into the glass matrix, enhancing the structural integrity without forming separate phase regions. Our findings demonstrate a significant improvement in radiation protection parameters, including mass attenuation coefficients and half-value layers, with higher La2O3 concentrations. These outcomes were also supported by the data obtained for Zeff and EBF values of G1-G4 glasses. The mechanical properties of the glasses were also investigated with the Makishima-Mackenzie model and it was observed that the elastic moduli were also affected by the addition of La2O3. The enhancements observed with La2O3 additions suggest promising avenues for developing advanced shielding materials, combining the inherent advantages of basalt glasses with the high atomic weight and electron density of lanthanum compounds.

Modeling of N and P-Type of Coaxial Ge Detectors Using MCNPX and the Effect of Dead Layer Variation on Its Response Function

Abstract This study assessed the response function of a p-type and n-type coaxial high-purity germanium (HPGe) detector via Monte Carlo N-Particle eXtended (MCNPX). MCNPX was employed to model the Coaxial Ge detectors, and for a precise simulation, the dimensions of the dead layer of germanium crystals were added. The dead layer was separated into front and lateral surfaces, and the thickness of each dead layer was modeled. In this work, the simulated detectors have been performed at different energy lines using a radioactive source Eu-152 to study the response function of each with dead layer variations for the front dead layer and study the range of relative deviation of the Monte Carlo simulation outputs from the manufactured declared data. The results proved that the n-type coaxial HPGe detector is more sensitive to the dead layer change than the p-type with a thick change of 0.01 mm. This research has significant effects on the efficiencies of the radiation detection systems in the energy range ∼ (120–1410) keV.

A new methodology for efficiency calibration of uncharacterized Ge detectors by using characterized Ge detectors

The measurement of gamma emitters natural radionuclides is a very relevant subject in environmental radioactivity in many fields. For this, a valid calibration based on the full-energy peak efficiency (FEPE) is essential, which can be carried out for gamma-ray spectrometry using Monte Carlo codes (Geant4, LabSOCS, MNCP, etc.) without needing a source preparation and with much less time consuming compared to experimental methodologies. Therefore, this work aims to develop a methodology for the FEPE determination of uncharacterized Ge detectors by using characterized Ge detectors with known FEPE. For this, a general relationship was found between the simulated FEPE (εsim) for characterized Ge detectors by LabSOCS and the experimental one (εexp) for uncharacterized Ge detectors obtained for a problem sample (phosphate rock (PR) in our case), where εsim and εexp were factorized using three correction factors: geometrical, photon self-absorption and true coincidence summing (TCS) effects. Thus, the εsim/εexp ratio (FEPER) was obtained for two couples of Ge detectors (2 characterized and 1 uncharacterized detectors), using 4 different cylindrical geometries (C) and 2 Marinelli (M) ones, and varying the sample thickness (h), and gamma energy (Eγ) (from 46 keV (210Pb) to 1765 keV (214Bi)). The consistency obtained for the FEPERs for C geometries suggested a constant geometric factor, finding some deviations for M geometries only at Eγ < 150 keV. Given a pair of detectors, the behavior of the FEPERs was found to be very similar for all geometries, and h at each specific Eγ. Moreover, a constat relationship between the FEPERs of both detector couples versus Eγ was found. Then, the influence of the TCS effects was also studied varying the distance between the geometry bottom and detector window. The developed methodology was also validated confirming the consistency of the FEPERs, which were found to be independent on the chemical composition and apparent density of the sample, supporting our theoretical hypothesis. Consequently, given that the FEPER was found to be independent on the sample type and h, using our developed methodology it is possible to obtain εexp for any sample, geometry and h using the FEPER, previously obtained at each Eγ for the sample selected for methodology development (PR in our case), and the εsim that is obtained for the desired case.

Exploring the Potential of Residual Impurities in Germanium Detectors for MeV-Scale Dark Matter Detection

The direct detection of MeV-scale dark matter (DM) particles hinges on achieving an exceptionally low-energy detection threshold. Germanium (Ge) detectors, meticulously tailored with precise impurity compositions, hold the potential to enhance sensitivity to energy levels below the sub-electronvolt (sub-eV) range. This study explores the behavior of residual impurities inherent to Ge detectors at helium temperatures, unveiling a captivating freeze-out phenomenon leading to the formation of excited localized states known as dipole states. Using compelling evidence from relative capacitance measurements obtained from two detectors, we elucidate the transition of impurity atoms from free charge states to these dipole states as the temperature drops from 11 to 6.5 K. Our investigation comprehensively covers the intricate formation of these dipole states in both n-type and p-type impurities. Furthermore, we shed light on the electric field generated by these dipole states, revealing their ability to trap charges and facilitate the creation of cluster dipole states. Confirming findings from previous measurements, we establish that these excited dipole states exhibit a binding energy of less than 10 meV, offering an exceptionally low detection threshold for MeV-scale DM. Building upon this concept, we propose the development of a 1-kg Ge detector with internal charge amplification—an innovative approach poised to surpass electrical noise and enable the detection of MeV-scale DM with unprecedented sensitivity.

Level structures of 96Tc and their microscopic description

High spin states in the 96Tc nucleus were populated in the 75As(28Si, 4p3n) fusion-evaporation reaction at E lab = 120 MeV and the de-excitations were investigated through in-beam γ-ray spectroscopic techniques using indian national gamma array spectrometer consisting of 18 clover Ge detectors. The present level scheme of the 96Tc nucleus has been extended substantially with the addition of about forty five new γ transitions. The level structures in 96Tc have been established up to excitation energy ∼10 MeV and angular momentum ∼25ℏ. Level structures of 96Tc nucleus are discussed in the framework of triaxial projected shell model calculations.

Influence of dead layer on the response function of planar and coaxial Ge detector using Monte Carlo method

Germanium crystals have a dead layer that causes a decrease in efficiency since the layer is not useful for detection but strongly attenuates photons. The thickness of this inactive layer is not well known due to the existence of a transition zone where photons are increasingly absorbed. Therefore, using data provided by manufacturers in the detector simulation model, some strong discrepancies appear by changing the dead layer. Investigations into the Ge detector response functions for gamma rays have been conducted using straightforward physical mechanisms implemented by Monte Carlo simulations. The detector response function feature's most probable interaction mechanisms are described. The Monte Carlo method is applied to simulate the calibration of a HPGe detector in order to determine the total inactive germanium layer thickness and the active volume that is needed in order to study the response function for both types of detectors. Results indicated a strong impact of dead layer variations on the response function of the simulated detectors.

Assessment of the use of tailings based on the legal requirements for radiation protection, from niobium mining in Minas Gerais – Brazil

Brazil is the world's largest supplier of niobium to industry, accounting for 98% of world production, with Minas Gerais supplying 80% of total production. The mineral exploration industry generates millions of tons of waste annually. In several mining industries, waste is considered a burden for companies. Based on the radiation protection exemptions for the disposal of mining waste, the study analyses the use of waste as a raw material for the construction industry. The minimum dose rate found for gamma radiation in the waste was 0.24 µSv/h and a maximum dose of 0.33 µSv/h, which corresponds to an annual dose above the population exposure limit. The radio concentrations from gamma spectrometric analyses with the Ge(HP) detector for the two samples are a maximum of 240 Bq/kg for Ra-226 and a maximum of 840 Bq/kg for Ra-228. Despite the dose values determined for gamma radiation, CNEN Resolution 179 of 2014 considers materials with natural radioactive concentrations of radium 226 and 228 of up to 1000 Bq/kg suitable for use in the cement industry. Nevertheless, further analysis must be carried out. Since the tailings contain a concentration of Ra-226 and the radio is a source of radon gas, new analyses need to be carried out targeting the exhalation of radon.

Directional-polarization correlations using EXILL

Eight EXOGAM-type, Ge-clover detectors of the EXILL array, arranged on an octagon plan and acting as Compton polarimeters, were used to measure directional-polarization correlations of γ rays populated in various processes. Measurements of γ radiation following neutron-induced fission of 235U and 241Pu targets; β --decay following fission; (n,γ) reactions on various stable targets and measurements using radioactive sources of 60Co, 133Ba and 152Eu were performed at the PF1B cold-neutron facility of the Institut Laue-Langevin in Grenoble. Digital electronics and a trigger-less acquisition system allowed the collection of signals from Ge detectors down to about 20 keV, providing measurements of linear polarization down to 120 keV. The precise sensitivity calibration was determined for the set of eight EXILL clover polarimeters in a range from 100 keV to 10000 keV. A new formula for calculating the directional-polarization correlations for the upper transition in a γγ cascade is derived from first principles. Directional-polarization correlations were measured for a few dozens of transitions in a number of nuclei, including values for twenty transitions in the 152Sm nucleus measured for the first time, and compared against the calculated values, to illustrate the quality of the technique. The combined analysis of angular and directional-polarization correlations is presented, which helps the determination of spin-parity assignments to excited levels.

Dark Matter Constraints from Isomeric ^{178m}Hf.

We describe a first measurement of the radiation from a ^{178m}Hf sample to search for dark matter. The γ flux from this sample, possessed by Los Alamos National Laboratory nuclear chemistry, was measured with a Ge detector at a distance of 1.2m due to its high activity. We search for γ's that cannot arise from the radioactive decay of ^{178m}Hf but might arise from the production of a nuclear state due to the inelastic scattering with dark matter. The limits obtained on this γ flux are then translated into constraints on the parameter space of inelastic dark matter. Finally, we describe the potential reach of future studies with ^{178m}Hf.

α(PS)–γ(Ge) digital anti-coincidence spectroscopy and its application to activity measurement of 225Ac

Activity of 225Ac was measured by the digital anti-coincidence spectroscopy technique using a 4πα–γ detector configuration, composed of a sandwich type 4π plastic scintillator and Ge detectors. Ultrathin plastic scintillators were used for selective detection of α-particles emitted from 225Ac and its progenies, and the α-counting efficiencies of a 4π plastic scintillation detector for individual nuclides in the decay chain were determined as well. A list-mode multichannel analyzer was employed to record coincidence/anti-coincidence events for off-line analyses. The time difference distribution spectra revealed α-particle emission following 213Po decay without β-particle interference from 213Bi.

Multiple scattering double Compton model: determination of intrinsic efficiencies by calculating electron energies

ABSTRACT For the measurement of the energy spectra generated by photons up to 320 keV (X-rays) that can be considered by the superposition of a set of monoenergetic photons, several types of detectors have been used, mainly Ge detectors. Each spectrum can be considered as the superposition of a beam of monoenergetic photons that contain a photoelectric peak, a Compton distribution, the characteristic radiation, and a multiple scattering region, which is located between the Compton edge and the photoelectric peak. In this article, a theoretical model is developed for finding the multiple scattering region. To this end, double Compton scattering is proposed, wherein the electron in motion after the first collision suffers a second Compton scattering by a photon going in the same direction. Using the theory of special relativity and the Lorentz invariants, the kinetic energy of the electron in motion is calculated. Then, with the obtained value and the new Klein–Nishina formula, the cross-section of the absorbed electrons is calculated as a function of its kinetic energy. The model fits correctly for the multiple scattering region from four sources with a conventional multichannel analyser and its associated electronics.

Sub-GeV dark matter searches with EDELWEISS: New results and prospects

The Edelweiss collaboration performs light Dark Matter (DM) particles searches with germanium bolometer collecting charge and phonon signals. Thanks to the Neganov-Trofimov-Luke (NTL) effect, a RMS resolution of 4.46 electron-hole pairs was obtained on a massive (200g) germanium detector instrumented with a NbSi Transition Edge Sensor (TES) operated underground at the Laboratoire Souterrain de Modane (LSM). This sensitivity made possible a search for WIMP using the Migdal effect down to 32 MeV/C^{2}2 and exclude cross-sections down to 10^{-29}−29 cm^22. It is the first measurement in cryogenic germanium with such thermal sensor, proving the high relevance of this technology. Furthermore, such TES have shown sensitivity to out-of-equilibrium phonons, paving the way for EDELWEISS new experience CRYOSEL. This is an important step in the development of Ge detectors with improved performance in the context of the EDELWEISS-SubGeV program.

Li2100deplMoO4 Scintillating Bolometers for Rare-Event Search Experiments

We report on the development of scintillating bolometers based on lithium molybdate crystals that contain molybdenum that has depleted into the double-β active isotope 100Mo (Li2100deplMoO4). We used two Li2100deplMoO4 cubic samples, each of which consisted of 45-millimeter sides and had a mass of 0.28 kg; these samples were produced following the purification and crystallization protocols developed for double-β search experiments with 100Mo-enriched Li2MoO4 crystals. Bolometric Ge detectors were utilized to register the scintillation photons that were emitted by the Li2100deplMoO4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc Underground Laboratory (Spain). We observed that the Li2100deplMoO4 scintillating bolometers were characterized by an excellent spectrometric performance (∼3–6 keV of FWHM at 0.24–2.6 MeV γs), moderate scintillation signal (∼0.3–0.6 keV/MeV scintillation-to-heat energy ratio, depending on the light collection conditions), and high radiopurity (228Th and 226Ra activities are below a few µBq/kg), which is comparable with the best reported results of low-temperature detectors that are based on Li2MoO4 using natural or 100Mo-enriched molybdenum content. The prospects of Li2100deplMoO4 bolometers for use in rare-event search experiments are briefly discussed.

Design and characterization of AmLi neutron sources for the LZ experiment

In this paper we describe the development, testing, and characterization of three low-emission rate AmLi neutron sources. The sources are used to calibrate the nuclear recoil response of the LUX-ZEPLIN (LZ) dark matter experiment. The sources' neutron emission rate was measured using 3He proportional tubes. The sources' gamma emissions were characterized using a high-purity germanium (HPGe) detector. Source-validated Geant4 Monte Carlo simulations allowed to calibrate the Ge and neutron detectors' responses.