Search

The determination of the plutonium isotopic composition by gamma spectrometry is one of the tasks performed by nuclear inspectors. It is typically measured using planar germanium detectors. The spectra are analysed with deconvolution codes, which calculate all isotopic abundances. The experimental results are then compared with the declared values and the acceptance criterion is often based on one unique isotope, 240Pu, to distinguish between reactor and weapon grade Pu. If the measurement is a part of a measurement series, it is possible to calculate covariance terms and carry out a more comprehensive comparison using Hotelling's test as recently presented in Berndt and Mortreau (2023) [1]. In this study, it was shown that the T2 test often rejects simulated false cases which are accepted if only the 240Pu abundance is considered. Hence, the T2 test should be preferred to the 240Pu criterion. In case of a single measurement, which is typical for inspections, the co-variance cannot be determined and the comprehensive calculation of the T2 test as performed in Berndt and Mortreau (2023) [1] cannot be applied. The purpose of the present paper is to consider approximations of the variance-covariance matrix to allow the application of the T2 test to isolated measurements. The results were then applied to more than 400 single measurements of Pu samples covering many different experimental conditions. [ABSTRACT FROM AUTHOR]

The use of High Purity Germanium detectors operated in ionization mode at cryogenic temperatures is investigated as an external background mitigation solution for bolometers used in rare-event search experiments. A simple experimental setup, running a 52-g Li 2 WO 4 bolometer sandwiched in-between two 2-cm thick High Purity Germanium cylindrical detectors in a dry cryostat, shows promising rejection to environmental gammas and atmospheric muons backgrounds. The acquired data are used together with a Monte Carlo simulation of the setup to extract the main contributions to the external backgrounds expected in an above ground experiment, such as e.g. current and future experimental efforts targeting the detection of coherent elastic neutrino-nucleus scattering at reactor facilities. Based on all these results, a 4 π coverage similar veto system achieving a O (10 keV) energy threshold is expected to achieve a ≳ 73% and a ≳ 92% rejection power for gamma-like and muon-like events, respectively. [ABSTRACT FROM AUTHOR]

The new DEspec Germanium Array Spectrometer (DEGAS), used at GSI/FAIR, includes bismuth germanate (BGO) scintillation detectors for active shielding to improve the sensitivity of its high-purity germanium (HPGe) detectors. The BGO detectors have a very high gamma-ray detection efficiency and can suppress background, such as Compton-scattered photons, by operating in an anti-coincidence veto mode with the germanium detectors. The BGO system was characterized and its performance was compared to simple gamma-ray propagation simulations. [ABSTRACT FROM AUTHOR]

Improved neutron inelastic scattering cross section data are needed to inform integral benchmark studies and advance applications in a wide variety of areas including nuclear energy, stockpile stewardship, nonproliferation, and space exploration. Neutron inelastic scattering also serves as a non-selective probe of low-lying nuclear structure. To help meet these needs, the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) was constructed at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. This array couples high-resolution γ -ray detectors and fast neutron detectors to achieve single and coincident n/ γ detection over a broad energy range. The current configuration of the array includes 26 organic liquid scintillators and four high-purity germanium detectors (two single-crystal and two four-crystal CLOVER detectors with two-fold segmentation). The array was constructed with minimal supporting material and designed to cover a wide range of secondary particle angles and energies with limited inter-element scattering. Data acquisition is accomplished using Mesytec MDPP-16 multi-channel high-resolution digital pulse processing modules. The array characteristics, including γ -ray and neutron energy resolution, timing resolution, and detection efficiency were measured and used to validate a Geant4 model of the array. The primary sources of neutron background and the uncertainties in the determination of incident and secondary neutron energy were assessed. GENESIS provides a new capability to address nuclear data needs and facilitates the advancement of a wide range of nuclear applications. [ABSTRACT FROM AUTHOR]

We have developed a photon detection system for muonic X-ray spectroscopy. The detector system consists of high-purity germanium detectors with BGO Compton suppressors. The signals from the detectors are readout with a digital acquisition system. The absolute energy accuracy, energy and timing resolutions, photo-peak efficiency, the performance of the Compton suppressor, and high count rate durability are studied with standard γ -ray sources and in-beam experiment using 27Al (p , γ) 28Si resonance reaction. The detection system was demonstrated at Paul Scherrer Institute. A calibration method for a photon detector at a muon facility using muonic X-rays of 197Au and 209Bi is proposed. [ABSTRACT FROM AUTHOR]

The Gaseous Detector with Germanium Tagging (GADGET) is a new detection system devoted to the measurement of weak, low-energy β -delayed proton decays relevant for nuclear astrophysics studies. It is comprised of a new gaseous Proton Detector equipped with a Micromegas readout for charged particle detection, surrounded by the existing Segmented Germanium Array (SeGA) for the high-resolution detection of the prompt γ -rays. In this work we describe in detail for the first time the design, construction, and operation of the GADGET system, including performance of the Proton Detector. We present the results of a recent commissioning experiment performed with 25Si beam at the National Superconducting Cyclotron Laboratory (NSCL). GADGET provided low-background, low-energy β -delayed proton detection with efficiency above 95%, and relatively good efficiency for proton-gamma coincidences (2.7% at 1.37 MeV). [ABSTRACT FROM AUTHOR]

Non-destructive gamma spectrometric measurements of the isotopic composition of plutonium are routinely carried out in the framework of nuclear safeguards inspections. High-resolution spectra of Pu obtained from planar Ge detectors are de-convoluted by means of special codes such as MGA or FRAM and these results are then applied when determining the total plutonium mass using neutron coincidence measurement techniques. The radiation emission of 242Pu is so weak that its abundance cannot be measured directly; hence isotopic correlations are utilized to estimate it in low and medium burn-up Pu material. The present work investigates the feasibility of determining the total Pu/Am ratio, exploiting X-ray fluorescence lines present in the plutonium spectrum. Combining the total Pu/Am ratio with individual Pu isotopic ratios to 241Am then allows an estimate of the 242Pu to be made. To this end, reference samples of plutonium, with an 241Am content comprised between 5 and 7 %, were measured using a planar germanium detector. The spectra were processed using MGA followed by quantification of the X-ray fluorescence peak of Americium, and then further calculations, including MCNP simulations. The conclusion of the present work is that, when the americium content of the sample is high enough to produce an Am K α 1 line which can be exploited, it is possible to indirectly determine the 242Pu abundance by analysing the X-ray fluorescent lines present in the plutonium gamma spectrum, thus raising the prospect to apply this method to cases for which the algorithms based on empirical correlations cannot be applied. [ABSTRACT FROM AUTHOR]

Charge trapping in germanium detectors will inevitably impact their excellent spectral performance. Disordered regions in the germanium crystal structure, either created in the material during processing or induced by radiation exposure, will affect the Charge Collection Efficiency (CCE), degrading the spectral resolution. Here we present numerical simulations of charge trapping effects on the anode and cathode signals for cross-strip germanium detectors. We discuss the assumptions behind our model of trapping, which accounts for both the drift length and thermal motion of the charge carriers. We present simulated CCE curves as a function of interaction depth within the detectors, and develop a technique for benchmarking these simulations against measured data. Comparison with measured CCE curves are presented. We are developing these numerical models with a goal of characterizing, and ultimately correcting, the effects of radiation damage on the spectral resolution of germanium cross-strip detectors. [ABSTRACT FROM AUTHOR]

A bismuth-germanate (BGO) anti-Compton shield (ACS) for Compex germanium detector modules was designed, built, and characterised. BGO performance was evaluated for light output and energy resolution. The response of the ACS shield and its impact on germanium detector spectra was measured for standard 60Co, 133Ba, and 137Cs sources. The results were compared to comprehensive Geant4 simulations. The ∼ 70 % improvement of the peak-to-total ratio for the 137Cs 662-keV γ -ray peak is in good agreement with expectations from the simulations. A 133Ba source exemplifies decay schemes of odd- A superheavy nuclei. Congruence between measured and simulated spectra indicates that the Compex plus ACS multi-detector module is well understood. [ABSTRACT FROM AUTHOR]

We present measurements of electron and hole trapping in three COSI germanium cross-strip detectors. By characterizing the relative charge collection efficiency (CCE) as a function of interaction depth, we show that intrinsic trapping of both electrons and holes have significant effects on the spectroscopic performance of the detectors. We find that both the electron and hole trapping vary from detector to detector, demonstrating the need for empirical trapping measurements and corrections. Using our measurements of charge trapping, we develop a continuous depth-dependent second-order energy correction procedure. We show that applying this empirical trapping correction produces significant improvements to spectral resolution and to the accuracy of the energy reconstruction. [ABSTRACT FROM AUTHOR]

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

Radiation transport models of two high purity germanium detectors, GeII and GeIII, located at the University of Alabama have been created in GEANT4 (Agostinelli et al., 2003) [1].These detectors have been used extensively for radioassay measurements of materials used in various low background experiments. The two models have been validated against actual data under several scenarios typically seen in radioassay measurements. The systematic uncertainties of the models for GeII and GeIII are estimated to be ∼ 12% and ∼ 9% respectively. [ABSTRACT FROM AUTHOR]

Fission and γ -emission probabilities induced by transfer or inelastic scattering reactions with light projectile nuclei are very valuable quantities for constraining the models that describe the de-excitation of heavy nuclei. We have developed an experimental set-up that allows us to simultaneously measure fission and γ -emission probabilities. The measurement of the γ -emission probability at excitation energies where the fission channel is open is challenging due to the intense background of γ rays emitted by the fission fragments. We discuss the procedure to subtract such a background and the constraints that this subtraction and other experimental conditions put on the set up. We show that our set-up complies with these constraints. [ABSTRACT FROM AUTHOR]

The selection of appropriate materials and their thicknesses, which should be used for germanium spectrometer shielding, is an important and complex task with the aim to reduce the contribution of background events to detector spectra. These background events have origin in the radioactive decay of environmental radionuclides, and also are produced by cosmic-ray muon induced secondary particles within shielding materials. In this work, the emission of gamma rays arising from members of U-238 and Th-232 series, as well as from K-40, distributed in the surroundings of the cylindrically-shaped shields was simulated, together with cosmic-ray muons of average energy 2 GeV, interacting with the shields. Different types of materials (Pb, Fe, Cu) including variations of the shield thickness were considered in simulations based on Geant4 software, while internal contamination of shielding material and radon buildup inside the shielding were not taken into account. The simulated spectra for germanium detector were analyzed and mutually compared. The results obtained were useful to provide optimal parameters for the shielding of germanium detectors against the external radiation — cosmic-ray muons and environmental gamma rays. • Environmental gammas and cosmic-ray muons were simulated in HPGe detector vicinity. • Pb, Fe, Cu shields and variations of their thicknesses were studied by simulations. • Contributions of gamma and muon-induced events to simulated spectra were analyzed. • Critical material thickness and background reduction for Pb, Fe and Cu were found. [ABSTRACT FROM AUTHOR]

Abstract A four-fold segmented n-type point-contact "Broad Energy" high-purity germanium detector, SegBEGe, has been characterised at the Max-Planck-Institut für Physik in Munich. The main characteristics of the detector are described and first measurements concerning the detector properties are presented. The possibility to use mirror pulses to determine source positions is discussed as well as charge losses observed close to the core contact. [ABSTRACT FROM AUTHOR]

Abstract XMASS-I is a single-phase liquid xenon detector whose purpose is direct detection of dark matter. To achieve the low background requirements necessary in the detector, a new model of photomultiplier tubes (PMTs), R10789, with a hexagonal window was developed based on the R8778 PMT used in the XMASS prototype detector. We screened the numerous component materials for their radioactivity. During development, the largest contributions to the reduction of radioactivity came from the stem and the dynode support. The glass stem was exchanged to the Kovar alloy one and the ceramic support were changed to the quartz one. R10789 is the first model of Hamamatsu Photonics K. K. that adopted these materials for low background purposes and provided a groundbreaking step for further reductions of radioactivity in PMTs. Measurements with germanium detectors showed 1.2 ± 0.3 mBq/PMT of 226Ra, less than 0.78 mBq/PMT of 228Ra, 9.1 ± 2.2 mBq/PMT of 40K, and 2.8 ± 0.2 mBq/PMT of 60Co. In this paper, the radioactive details of the developed R10789 are described together with our screening methods and the components of the PMT. [ABSTRACT FROM AUTHOR]

Abstract Compton γ -ray sources have been in operation for over 30 years with new facilities being under construction or proposed. The gamma beam system under implementation at the Extreme Light Infrastructure - Nuclear Physics facility in Romania will deliver brilliant γ -ray beams with energies up to 19.5 MeV. Several instruments for measuring the parameters of the γ -ray beam are under development at ELI-NP. One of these instruments based on a High Purity Germanium detector is routinely used for beam energy measurements at other facilities. Here we investigate the use of a High Purity Germanium detector to continuously monitor the intensity of the ELI-NP gamma beam by measuring the inelastic scattering of photons. This method relies on both experimental and simulated data and it has been successfully tested during a recent experiment at the High Intensity γ -ray Source facility. [ABSTRACT FROM AUTHOR]

Abstract Monte Carlo calculations and artificial intelligence prediction techniques were executed to estimate the uranium content of the isotope U-235 of uranium oxide (U 3 O 8) standards. Five uranium oxide (U 3 O 8) standards with different enrichments were used in this study. The count rate was measured experimentally using Hyper-Pure Germanium detector (HPGe) and MCNP-5 Monte Carlo transport code to estimate 235U mass of standard nuclear materials. The acquired results were compared with declared values. Finally, Artificial Neural Network (ANN) simulation was used to get the results of count rate and U-235 mass. The results were matched with the experiment within an accuracy of less than 2%. [ABSTRACT FROM AUTHOR]

Abstract When determining the activity concentration of radionuclides using gamma-ray spectrometry the Full Energy Peak Efficiency (FEPE) for the energies of interest must be known. Determination of the FEPE can be made by means of either experimental calibration or theoretical–mathematical methods, such as Monte Carlo simulations. Given the difficulties related to experimental calibration and improvements in the capabilities of modern computers, Monte Carlo simulation is an increasingly widely used alternative, but requires an accurate model of the detector. The purpose of this work is to generate and validate a computational model, based on Monte Carlo simulation, of an HPGe well detector that permits the performance of FEPE calculations with appropriate precision and accuracy for the measurement of environmental samples. To achieve this, an optimization methodology is applied to the model that minimizes the differences between a set of computational FEPEs and a set of experimental FEPEs used as a benchmark. The resulting optimized model is used to calculate computational FEPEs for 25 different samples with different reference materials and sample heights, which are measured by means of the well detector modeled here. To validate the optimized model, the abovementioned computational FEPEs are used during the calibration of the corresponding spectra, to enable the subsequent comparison of the results of the analyses with the expected values. The measured activities differ from the reference values by less than 10% in most cases and are compatible with these considering the uncertainties involved, thus confirming the validity of the model. Highlights • A HPGe well detector has been modeled using the PENELOPE Code. • Experimental FEPEs have been used as reference. • The model was optimized using the Differential Evolution algorithm. • The model has been validated using reference materials. • Good agreement observed between reference and measured activity concentrations. [ABSTRACT FROM AUTHOR]

Nuclear materials characterization in 870 L cemented waste drums is challenging due to significant neutron and gamma ray attenuation. Among the existing non-destructive approaches, photon active interrogation is of particular interest. A LINAC accelerates electrons to energies greater than 10 MeV, leading to highly penetrating interrogating bremsstrahlung photons that can reach nuclear materials in the depth of the 870 L waste drum and allow the detection of delayed gamma rays emitted by photofission products. Because the interrogating photon and neutron fluxes are extremely high during irradiation, measurements with high purity germanium detectors are usually performed after a long irradiation time, for example by moving the detector or the waste drum. Therefore, such measurements are only sensitive to delayed gamma rays associated to photofission products having sufficient long half-life of at least tens of seconds, which cuts a valuable signal coming from fission products with a shorter half-life. In this paper, we report gamma rays measurements of very short lived photofission products using a 3 in × 3 in cylindrical LaBr 3 (Ce) fast scintillation detector. A depleted uranium sample was irradiated by a pulsed bremsstrahlung source with maximum energy 17.5 MeV in a macro pulsing mode (1 s irradiation, 2 s cooling). This allowed to acquire a strong delayed gamma signal within a time window of 2 s. A clear signature of nuclear materials was observed even in the depth of a concrete mock-up, with an excellent signal-to-noise ratio beyond 3.5 MeV where the background of nonnuclear activated materials is negligible. These results are compared to a semi analytical model that qualitatively agrees but underestimates the measurements by a constant factor 1.7, probably caused by a wrong beam intensity normalization. Indeed, in this work the LINAC pulse time structure (macro pulsing) was different from its nominal working point used to characterize the beam (usual pulsing mode). Since it allows direct calculations of the detector response to delayed gamma-ray photofission measurements, this model is a fast calculation alternative to time-consuming Monte Carlo simulations, in view of further studies that will follow this feasibility demonstration. [ABSTRACT FROM AUTHOR]

Conversion electron spectroscopy is a valuable tool in nuclear structure studies, but the complex spectra resulting from the high density of levels in the spectra of heavy nuclei make it difficult to extract the most beneficial information from singles measurements. This work reports on the transformation of ICEBall, which was a mini-orange spectrometer that was used in coincidence with various Germanium detector arrays, to the improved fInternal conveRsion Electron Ball (fIREBall) spectrometer for the improved measurements of E0 transitions and conversion electron coefficients. A combination of FreeCAD, COMSOL, and Geant4 simulations were implemented to optimize the geometries for the magnet filters used in the spectrometer to significantly improve the efficiency of electron collection in the energy range of interest 200 keV-1 MeV. The array of six mini-orange Si(Li) detectors are to be replaced with six new, thicker Si(Li) detectors. Experimental tests reported here show a peak improvement in absolute efficiency from 2.8% to 5.3% for the 482 keV K electron line in 207Bi for a single magnet filter and detector pair. [ABSTRACT FROM AUTHOR]

Abstract In indirectly driven inertial confinement fusion, a high-purity germanium detector is widely used in the calibration of various X-ray detectors as a quantitative spectrum detector for the irradiating X-ray. However, the intrinsic peak efficiency of the high-purity germanium detector, which is the foundation of its applications, has not been investigated in depth. In this work, an optimized data-processing method is developed to explore the intrinsic peak efficiency of the high-purity germanium detector, based on calibration experiments. The intrinsic peak efficiency of the detector is absolutely and accurately calibrated and simulated for X-ray energy in the range of 5.48–302.85 keV. The experimental and simulated results, which agree well, are analyzed and explained in detail. The efficiency curve obtained from the data reveals the rise, flat, and fall characters. In addition, the impact of the absorption edge, which is located at 11.10 keV, on the efficiency curve was found and explained in terms of the escape of the excited K α lines. This work will improve the calibration efficiency of various X-ray detectors based on the high-purity germanium detector, and help in advancing the quantitative understanding of the detection results in inertial confinement fusion. [ABSTRACT FROM AUTHOR]

The lifetimes of nuclear excited states are important observables in nuclear physics. Their precise measurement is of key importance for developing and testing nuclear models as they are directly linked with the quantum nature of the nuclear system. The γ - γ timing technique represents a direct lifetime determination by means of time-difference measurements between the γ rays which directly feed and decay from a nuclear excited state. Using arrays of very-fast scintillator detectors, picosecond-sensitive time-difference measurements can be performed. We propose to construct a symmetric energy–energy–time cube as is usually done to perform γ - γ coincidence analyses and lifetime determination with high-resolution germanium detectors. By construction, a symmetric mean time-walk characteristics is obtained, that can be precisely determined and used as a single time correction for all the data independently of the detectors. We present the results of timing characteristics measurements of an array with six LaBr 3 (Ce) detectors, as obtained using a 152 Eu point γ -ray source. Compared with a single detector pair, the time resolution of the symmetrised time-difference spectra of the array is nearly unaffected. [ABSTRACT FROM AUTHOR]

Interactions of neutrons with a high-purity germanium detector were studied experimentally and by simulations using the GEANT4 tool. Elastic and inelastic scattering of fast neutrons as well as neutron capture on Ge nuclei were observed. Peaks induced by inelastic scattering of neutrons on 70 Ge, 72 Ge, 73 Ge, 74 Ge and 76 Ge were well visible in the γ -ray spectra. In addition, peaks due to inelastic scattering of neutrons on copper and lead nuclei, including the well-known peak of 208 Pb at 2614.51 keV, were detected. The GEANT4 simulations showed that the simulated spectrum was in a good agreement with the experimental one. Differences between the simulated and the measured spectra were due to the high γ -ray intensity of the used neutron source, physics implemented in GEANT4 and contamination of the neutron source. [ABSTRACT FROM AUTHOR]

The SIGMA Germanium detector has the potential to revolutionise γ -ray spectroscopy, providing superior energy and position resolving capabilities compared with current large volume state-of-the-art Germanium detectors. The theoretical position resolution of the detector as a function of γ -ray interaction position has been studied using simulated detector signals. A study of the effects of RMS noise at various energies has been presented with the position resolution ranging from 0.33 mm FWHM at E γ = 1 MeV , to 0.41 mm at E γ = 150 keV. An additional investigation into the effects pulse alignment have on pulse shape analysis and in turn, position resolution has been performed. The theoretical performance of SIGMA operating in an experimental setting is presented for use as a standalone detector and as part of an ancillary system. [ABSTRACT FROM AUTHOR]

Measurements of uranium enrichment in UF 6 transit cylinders are an important nuclear safeguards verification task, which is performed using a non-destructive assay method, the traditional enrichment meter, which involves measuring the count rate of the 186 keV gamma ray. This provides a direct measure of the 235 U enrichment. Measurements are typically performed using either high-resolution detectors (Germanium) with e-cooling and battery operation, or portable devices equipped with low resolution detectors (NaI). Despite good results being achieved when measuring Low Enriched Uranium in 30B type cylinders and natural uranium in 48Y type containers using both detector systems, there are situations, which preclude the use of one or both of these systems. The focus of this work is to address some of the recognized limitations in relation to the current use of the above detector systems by considering the feasibility of an inspection instrument for 235 U enrichment measurements on UF 6 cylinders using the compact and light Cadmium Zinc Telluride (CZT) detectors. In the present work, test measurements were carried out, under field conditions and on full-size objects, with different CZT detectors, in particular for situations where existing systems cannot be used e.g. for stacks of 48Y type containers with depleted uranium. The main result of this study shows that the CZT detectors, actually a cluster of four μ CZT1500 micro spectrometers provide as good results as the germanium detector in the ORTEC Micro-trans SPEC HPGe Portable spectrometer, and most importantly in particular for natural and depleted uranium in 48Y cylinders. [ABSTRACT FROM AUTHOR]

The p-type point-contact germanium detectors have been adopted for light dark matter WIMP searches and the studies of low energy neutrino physics. These detectors exhibit anomalous behavior to events located at the surface layer. The previous spectral shape method to identify these surface events from the bulk signals relies on spectral shape assumptions and the use of external calibration sources. We report an improved method in separating them by taking the ratios among different categories of in situ event samples as calibration sources. Data from CDEX-1 and TEXONO experiments are re-examined using the ratio method. Results are shown to be consistent with the spectral shape method. [ABSTRACT FROM AUTHOR]

High-resolution gamma-ray spectrometers are required for applications in nuclear safeguards, emergency response, and fundamental nuclear physics. To overcome one of the shortcomings of conventional High Purity Germanium (HPGe) detectors, we have developed a prototype device capable of achieving high event throughput and high energy resolution at very high count rates. This device, the design of which we have previously reported on, features a planar HPGe crystal with a reduced-capacitance strip electrode geometry. This design is intended to provide good energy resolution at the short shaping or digital filter times that are required for high rate operation and which are enabled by the fast charge collection afforded by the planar geometry crystal. In this work, we report on the initial performance of the system at count rates up to and including two million counts per second. [ABSTRACT FROM AUTHOR]

The Majorana Demonstrator is an array of point-contact Ge detectors fabricated from Ge isotopically enriched to 88% in 76 Ge to search for neutrinoless double beta decay. The processing of Ge for germanium detectors is a well-known technology. However, because of the high cost of Ge enriched in 76 Ge special procedures were required to maximize the yield of detector mass and to minimize exposure to cosmic rays. These procedures include careful accounting for the material; shielding it to reduce cosmogenic generation of radioactive isotopes; and development of special reprocessing techniques for contaminated solid germanium, shavings, grindings, acid etchant and cutting fluids from detector fabrication. Processing procedures were developed that resulted in a total yield in detector mass of 70%. However, none of the acid-etch solution and only 50% of the cutting fluids from detector fabrication were reprocessed. Had they been processed, the projections for the recovery yield would be between 80% and 85%. Maximizing yield is critical to justify a possible future ton-scale experiment. A process for recovery of germanium from the acid-etch solution was developed with yield of about 90%. All material was shielded or stored underground whenever possible to minimize the formation of 68 Ge by cosmic rays, which contributes background in the double-beta decay region of interest and cannot be removed by zone refinement and crystal growth. Formation of 68 Ge was reduced by a significant factor over that in natural abundance detectors not protected from cosmic rays. [ABSTRACT FROM AUTHOR]

The AGATA (Advanced GAmma Tracking Array) tracking detector is being designed to far surpass the performance of the previous generation, Compton-suppressed arrays. In this paper, a characterization of AGATA is provided based on data from the second GSI campaign. Emphasis is placed on the proper corrections required to extract the absolute photopeak efficiency and peak-to-total ratio. The performance after tracking is extracted and GEANT4 simulations are used both to understand the results and to scale the measurements up to predicted values for the full 4 π implementation of the device. [ABSTRACT FROM AUTHOR]

The Majorana Collaboration is searching for the neutrinoless double-beta decay of the nucleus 76 Ge. The Majorana Demonstrator is an array of germanium detectors deployed with the aim of implementing background reduction techniques suitable for a 1-ton 76 Ge-based search. The ultra low-background conditions require regular calibrations to verify proper function of the detectors. Radioactive line sources can be deployed around the cryostats containing the detectors for regular energy calibrations. When measuring in low-background mode, these line sources have to be stored outside the shielding so they do not contribute to the background. The deployment and the retraction of the source are designed to be controlled by the data acquisition system and do not require any direct human interaction. In this paper, we detail the design requirements and implementation of the calibration apparatus, which provides the event rates needed to define the pulse-shape cuts and energy calibration used in the final analysis as well as data that can be compared to simulations. [ABSTRACT FROM AUTHOR]

The internal contamination (radio-purity) of a cesium hafnium chloride (Cs 2 HfCl 6 ) crystal scintillator and its starting material (CsCl, HfCl 4 initial and after 3-fold static sublimation purification) was studied by HR-ICP-MS and with an ultra-low-background high purity germanium (ULB-HPGe) detector deep underground. This study was conducted for the purpose of assessing the feasibility of using CHC as a potential detector to the search for rare α decay occurring in Hafnium isotopes. Despite the low radio-purity of starting material, the resulting analysis concluded that the grown CHC crystal is free of nuclides of the U/Th natural decay chain. Only a limit was set on their activities to a few mBq/kg. However, the crystal was found to contain artificial and cosmogenic radionuclides: 137 Cs at 0.8 Bq/kg, 132 Cs at 25 mBq/kg, 134 Cs at 52 mBq/kg and 181 Hf at 14 mBq/kg. [ABSTRACT FROM AUTHOR]

We have characterized, for the first time, an n-type segmented inverted coaxial point-contact detector. This novel detector technology relies on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ -ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in this detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 ± 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values. [ABSTRACT FROM AUTHOR]

The position sensitivity of a planar segmented double-sided germanium strip detector, with 10 × 10 electrical segmentation in orthogonal directions, has been studied using the coincidence method. The coincidences were set up between an imaging scanner and the PSPGe (Position Sensitive Planar Germanium) detector using a positron source, 22Na, and analyzed by employing the Positron Annihilation Correlation principle. A collimated 241Am source scan was also performed to find position resolution along X and Y axes using low energy gamma-ray source. The primary objective of this work is to study the charge carrier transportation for gamma-ray interactions inside the PSPGe detector. In order to select the electrodes of interest and to obtain the pulse shapes for each event, two-dimensional images have been processed. The net charge induced on the surface of the electrode, calculated using the pulse shape analysis procedure, has been used to profile the position resolution and gamma interaction depth. The present study is an input for the deployment of PSPGe detector in the future decay spectroscopy experiments to be performed at the Facility for Antiproton and Ion Research (FAIR) in Germany. This work investigates the gamma interaction depth by calculating the rise-time of traces stored for each gamma interaction inside the detector volume, providing ≈ 1 mm resolution along the depth. The position resolution of the detector in lateral directions, determined using the amplitude difference of the transient charges, has also been found to be ≈ 1 mm. [ABSTRACT FROM AUTHOR]

The use of segmented HPGe detectors for gamma-ray tracking applications is well established. The spectroscopic capabilities of these detectors make them most suitable for such applications. For similar reasons, the use of such detectors in the tomographic measurement of irradiated nuclear fuel has also been envisioned. Especially, these detectors can facilitate faster fuel examination with excellent energy resolution. We have proposed and designed a novel planar segmented HPGe detector for use in gamma emission tomography. The design of the detector segmentation and the mode of operation is unique and offers six simultaneous detection channels for tomographic measurements. This work reports the first experimental evaluation of the performance of the detector. Important characteristics of the detector have been obtained, such as energy resolution of the segments in 1-fold (one segment) and 2-fold (two segments) modes, throughput curves, crosstalk energy corrections, and mislocalisation rate. Collimated source tests have been performed and the results have been compared with the MCNP simulations results. The obtained results are as expected and in good agreement with the simulation results, and it is estimated that using this detector can speed up the data collection by 3.2 times in comparison to an unsegmented detector of the same overall dimensions, in a tomographic application. Further improvements are foreseeable if scaling up to a larger detector with greater segmentation. [ABSTRACT FROM AUTHOR]

Positron annihilation Doppler broadening spectroscopy characterizes lattice point defects and is sensitive to very small vacancy densities. High-purity germanium detectors are generally used for recording the Doppler broadening spectrum because they provide good energy resolution and stability. However, the energy resolution of a germanium detector is somewhat dependent on the photon absorption geometry in the detector crystal. This change in the energy resolution changes also the Doppler broadening parameters. To observe the dependency of the resolution function and the Doppler broadening parameters, we performed experiments on Si samples in standard sandwich configuration with a Na-22 source. We changed the radiation geometry of the incident gamma photons via altering the distance of the sample-source package from the detector and by adding steel between the source and the detector. We observed the change of the absorption geometry in the germanium detector crystal by doing Monte Carlo simulations. The aim of this study is to help understand and decide what is the best way to compare the Doppler broadening parameters obtained with different measurement setups and even with the same setup when the geometry in the measurements has changed. [ABSTRACT FROM AUTHOR]

In this work, we have developed a computational methodology for characterizing HPGe detectors by implementing in parallel a multi-objective evolutionary algorithm, together with a Monte Carlo simulation code. The evolutionary algorithm is used for searching the geometrical parameters of a model of detector by minimizing the differences between the efficiencies calculated by Monte Carlo simulation and two reference sets of Full Energy Peak Efficiencies (FEPEs) corresponding to two given sample geometries, a beaker of small diameter laid over the detector window and a beaker of large capacity which wrap the detector. This methodology is a generalization of a previously published work, which was limited to beakers placed over the window of the detector with a diameter equal or smaller than the crystal diameter, so that the crystal mount cap (which surround the lateral surface of the crystal), was not considered in the detector model. The generalization has been accomplished not only by including such a mount cap in the model, but also using multi-objective optimization instead of mono-objective, with the aim of building a model sufficiently accurate for a wider variety of beakers commonly used for the measurement of environmental samples by gamma spectrometry, like for instance, Marinellis, Petris, or any other beaker with a diameter larger than the crystal diameter, for which part of the detected radiation have to pass through the mount cap. The proposed methodology has been applied to an HPGe XtRa detector, providing a model of detector which has been successfully verificated for different source-detector geometries and materials and experimentally validated using CRMs. [ABSTRACT FROM AUTHOR]

A detailed study of alpha interactions on the passivation layer on the end-plate of a true-coaxial high-purity germanium detector is presented. The observation of alpha events on such a surface indicates an unexpectedly thin so-called “effective dead layer” of less than 20 µm thickness. In addition, the influence of the metalisation close to the end-plate on the time evolution of the output pulses is discussed. The results indicate that alpha contamination can result in events which could be mistaken as signals for neutrinoless double beta decay and provide some guidance on how to prevent this. [ABSTRACT FROM AUTHOR]

Hyperion is a new high-efficiency charged-particle γ -ray detector array which consists of a segmented silicon telescope for charged-particle detection and up to fourteen high-purity germanium clover detectors for the detection of coincident γ rays. The array will be used in nuclear physics measurements and Stockpile Stewardship studies and replaces the STARLiTeR array. This article discusses the features of the array and presents data collected with the array in the commissioning experiment. [ABSTRACT FROM AUTHOR]

In order to explore possible improvements of the existing techniques developed to estimate the neutron fluence in low-background Ge-spectroscopy systems, gamma spectra were collected by a HPGe detector in the presence of the 252 Cf spontaneous fission neutron source. The spectra were taken with and without a Cd envelope on the detector dipstick, with different thicknesses of plastic used to slow down neutrons. We have analyzed the complex 595.8 keV gamma peak, as well as several more gamma peaks following the neutron interactions in the detector itself and surroundings materials. The investigation shows that some changes of the initial neutron spectra can be monitored by the analysis of the 595.8 keV gamma peak. We have found good agreement in the intensity changes between the long-tail component of the 595.8 keV and the 691 keV gamma peak ( 72 Ge(n,n′) 72 Ge reaction), usually used for the estimation of the fast neutron fluence. Results also suggest that the thermal neutrons can have a stronger influence on creation of the Gaussian-like part of 595.8 keV peak, than on the 139 keV one following 74 Ge(n,γ) 75m Ge reaction and used in the standard methods (Škoro et al., 1992) [8] for determination of the thermal neutron flux. [ABSTRACT FROM AUTHOR]

A technique for elucidating β -decay schemes of isotopes with a large density of states at low excitation energy has been developed, in which a Broad Energy Germanium (BEGe) detector is used in conjunction with coaxial hyper-pure germanium detectors. The power of this technique is demonstrated using the example of 183 Hg decay. Mass-separated samples of 183 Hg were produced by a deposition of the low-energy radioactive-ion beam delivered by the ISOLDE facility at CERN. The excellent energy resolution of the BEGe detector allowed γ -ray energies to be determined with a precision of a few tens of eV, which was sufficient for the analysis of the Rydberg-Ritz combinations (in conjunction with γ - γ coincidences) in the level scheme. The timestamped structure of the data was used for unambiguous separation of γ rays arising from the decay of 183 Hg from those due to the daughter decays. [ABSTRACT FROM AUTHOR]

Since the advent of the new generation of germanium detector arrays for low-energy nuclear physics experiments utilizing gamma-ray tracking, the challenges associated with track-reconstruction methods have been extensively studied. In the present work an approach based on recent developments in machine learning was used to address the problem. Here, a graph neural network was constructed and trained on data simulated in Geant4 in order to attempt track reconstruction of gamma rays below 1 MeV in a spherical shell geometry of pure germanium. Using a thick-shell geometry, and simulated data without energy- and position uncertainties the network achieved a reconstruction rate above 80% for complete tracks, and a combined peak-to-total value of 85% for energy spectra with four discrete peaks. For data with added noise, i.e. finite resolution in interaction-point position and energy, the corresponding peak-to-total ratio dropped to 74%. The track reconstruction was stable across multiplicities 1–10 but showed an increased error frequency in the energy range between 50 keV and 250 keV. To specifically study the complication of gamma tracks lost by out-scattering from the detector volume, a thin-shell (9 cm thickness) geometry was used together with a modified version of the GNN framework. By letting the GNN code identify and discriminate the out-scatter events, an improvement of the P/T value from 66% to 75% was found for the packed, noisy data. For the sake of comparison the new GNN model with existing gamma-ray tracking methods, a separate instance of the network was trained on slightly higher energies (up to 1.5 MeV) and multiplicities (up to 15) to evaluate 1.332 MeV photon cascade data in terms of P/T and photo-peak efficiency. The results for this GNN data set, with P/T values at 85% for single tracks and 74% for multiplicity 15, show clear promise when compared to the existing tracking methods. [ABSTRACT FROM AUTHOR]

Neutrinoless double beta (0 ν β β) decay is a powerful tool to investigate lepton number violation and to assess the neutrino nature. Among many experiments in the field, LEGEND-200, will search for 0 ν β β decay in 76Ge, using about 200 kg of germanium detectors deployed in ultra-pure Liquid Argon (LAr). The LAr is used as cooling medium and active scintillation veto through LAr instrumentation. The LAr instrumentation was one of the key factors in achieving the lowest background index and the best half-life sensitivity in the previous GERDA experiment. Thus an upgraded version with improved optical coverage, is adopted in LEGEND-200 to actively veto background events in the region of interest, i.e. around the Q-value of the 0 ν β β decay. [ABSTRACT FROM AUTHOR]

Analyzing concentrations/grades for interested valuable elements in mineral ores with low detection limit, high accuracy, high precision and high assay speed is essential in the whole processing chain for economic benefits. In this work, a method using delayed gamma rays from neutron activation, based on an e-LINAC driven photoneutron source and a high-purity germanium detector, is introduced. It fulfills the requirements in analysis of gold ores including low detection limit (0.1 g/t), high precision and high assay speed (several minutes per sample for fulfilling the standard requirements). Comparing to the traditional method of fire assay, this method shows the advantages of low labor consumption, low time consuming, no toxic pollution, multi-element analysis ability and non-destruction. [ABSTRACT FROM AUTHOR]

In past years efforts have concentrated on the development of arrays of Silicon Drift Detectors for X-ray spectroscopy. This is in stark contrast to the little effort that has been devoted to the improvement of germanium detectors, in particular for synchrotron applications. Germanium detectors have better energy resolution and are more efficient in detecting high energy photons than silicon detectors. In this context, the detector consortium of the European project LEAPS-INNOV has set an ambitious R&D program devoted to the development of a new generation of multi-element monolithic germanium detectors for X-ray detection. In order to improve the performance of the detector under development, simulations of the different detector design options have been performed. In this contribution, the efforts in terms of R&D are outlined with a focus on the modelization of the detector geometry and first performance results. These performance results show that a signal-to-background ratio larger than 1000 can be achieved in the energy range of interest from 5 keV to 100 keV. [ABSTRACT FROM AUTHOR]

The high brilliance and coherent beams resulting from recent upgraded synchrotron radiation facilities open the way for a large range of experiments, where detectors play a key role in the techniques and methods developed to fully exploit the upgraded synchrotron. For instance, one of the major limitations of XAFS experiment is the performance of the detectors. In order to be able to measure more challenging samples and to cope with the very high photon flux of the current and future (diffraction limited) sources, technological developments of detectors are necessary. In this framework, the germanium detector developed in the European project LEAPS-INNOV aims at improving several technological aspects. This type of detector represents a very important class of instruments for X-ray spectroscopy due to the fact that they enable to detect efficiently photons of considerable higher energy with respect to silicon detectors. The objective of this project consists in pushing the detector performance beyond the state-of-the-art. Preliminary layout and main choices for the design studies of this new detector are presented in this paper. [ABSTRACT FROM AUTHOR]

Delayed gamma rays following neutron activation, induced by a 6 MeV linear electron accelerator (linac) coupled to a deuterium oxide photo–neutron conversion target, are simulated with MCNP6.1. The 1039 keV copper activation gamma peak is detected with a 33% relative efficiency hyper pure germanium detector. Two copper distributions were assessed for a 2-hour irradiation followed by a 2-hour counting configuration. Homogeneously distributed copper in a planar scrap metal matrix shows 65Cu detection limits of 10.01 g. A solid copper sample, modeled at five distinct positions in the planar scrap metal matrix, exhibits detection limits from 8.27 to 14.27 g. [ABSTRACT FROM AUTHOR]

Radionuclide identification and quantification are a serious concern for many applications as for in situ monitoring at nuclear facilities, laboratory analysis, special nuclear materials detection, environmental monitoring, and waste measurements. High resolution gamma-ray spectrometry based on high purity germanium diode detectors is the best solution available for isotopic identification. Over the last decades, methods have been developed to improve gamma spectra analysis. However, some difficulties remain in the analysis when full energy peaks are folded together with high ratio between their amplitudes, and when the Compton background is much larger compared to the signal of a single peak. In this context, this study deals with the comparison between a conventional analysis based on “iterative peak fitting deconvolution” method and a “nonparametric Bayesian deconvolution” approach developed by the CEA LIST and implemented into the SINBAD code. The iterative peak fit deconvolution is used in this study as a reference method largely validated by industrial standards to unfold complex spectra from HPGe detectors. Complex cases of spectra are studied from IAEA benchmark protocol tests and with measured spectra. The SINBAD code shows promising deconvolution capabilities compared to the conventional method without any expert parameter fine tuning. [ABSTRACT FROM AUTHOR]

In this paper, we provide a formalism for the characterization of tracking arrays with emphasis on the proper corrections required to extract their photopeak efficiencies and peak-to-total ratios. The methods are first applied to Gammasphere, a well characterized 4 π array based on the principle of Compton suppression, and subsequently to GRETINA. The tracking efficiencies are then discussed and some guidelines as to what clustering angle to use in the tracking algorithm are presented. It was possible, using GEANT4 simulations, to scale the measured efficiencies up to the expected values for the full 4 π implementation of GRETA. [ABSTRACT FROM AUTHOR]