Array Of High-purity Germanium Detectors Research Articles

Nondestructive determination of isotopic abundance using multi-energy nuclear resonance fluorescence driven by laser Compton scattering source

We report on the quantitative nondestructive analysis of the natural isotopic abundances of hafnium and tungsten elements using nuclear resonance fluorescence. Metallic samples of hafnium and tungsten were irradiated to six quasi-monochromatic γ-ray beams generated by laser Compton scattering in the energy range of 2.4–3.2 MeV. Multiple nuclei were simultaneously excited at each of the six γ-ray beam energies. A high-purity germanium detector array detected deexcitations of the nuclei. In total, 51 transitions were unprecedentedly employed to estimate the isotopic abundances of heavy elements nondestructively. The estimated abundances of three hafnium isotopes and three tungsten isotopes are consistent with standard known natural abundances within the experimental uncertainties. The deviation from the standard values ranges from 0.18% to 1.36%.

Constraints on the Decay of ^{180m}Ta.

^{180m}Ta is a rare nuclear isomer whose decay has never been observed. Its remarkably long lifetime surpasses the half-lives of all other known β and electron capture decays due to the large K-spin differences and small energy differences between the isomeric and lower-energy states. Detecting its decay presents a significant experimental challenge but could shed light on neutrino-induced nucleosynthesis mechanisms, the nature of dark matter, and K-spin violation. For this study, we repurposed the Majorana Demonstrator, an experimental search for the neutrinoless double-beta decay of ^{76}Ge using an array of high-purity germanium detectors, to search for the decay of ^{180m}Ta. More than 17kg, the largest amount of tantalum metal ever used for such a search, was installed within the ultralow-background detector array. In this Letter, we present results from the first year of Ta data taking and provide an updated limit for the ^{180m}Ta half-life on the different decay channels. With new limits up to 1.5×10^{19} yr, we improved existing limits by 1-2 orders of magnitude which are the most sensitive searches for a single β and electron capture decay ever achieved. Over all channels, the decay can be excluded for T_{1/2}<0.29×10^{18} yr.

Liquid argon light collection and veto modeling in GERDA Phase II

The ability to detect liquid argon scintillation light from within a densely packed high-purity germanium detector array allowed the Gerda experiment to reach an exceptionally low background rate in the search for neutrinoless double beta decay of {}^{76}Ge. Proper modeling of the light propagation throughout the experimental setup, from any origin in the liquid argon volume to its eventual detection by the novel light read-out system, provides insight into the rejection capability and is a necessary ingredient to obtain robust background predictions. In this paper, we present a model of the Gerda liquid argon veto, as obtained by Monte Carlo simulations and constrained by calibration data, and highlight its application for background decomposition.

Multiparticle-hole excitations in nuclei near N = Z = 20: $$^{41}$$K

This experimental study of high-spin structure near \(N = Z = 20\) nuclei was focused on \(^{41}\)K, but will also mention three newly observed \(\gamma \) transitions in \(^{41}\)Ca observed in the same reaction. High-spin states were populated using the \(^{26}\)Mg(\(^{18}\)O, \(p2n\gamma \))\(^{41}\)K and \(^{26}\)Mg(\(^{18}\)O, \(3n\gamma \))\(^{41}\)Ca reactions. The experiment was carried out at an incident beam energy of 50 MeV at the Florida State University (FSU) John D. Fox Superconducting Linear Accelerator Laboratory and used the FSU high-purity germanium detector array. The \(^{41}\)K level scheme was extended to 12325 keV, possibly with J\(^{\pi }\) = 25/2\(^-\) or 27/2\(^+\), by means of 25 new transitions and that of \(^{41}\)Ca to 9916 keV. Linear polarization and a measure of angular distribution results are also reported and used to provide information on the spins and parities of several states in the \(^{41}\)K level scheme. The results have been compared to the spsdpf cross-shell FSU shell model interaction calculations. The theoretical results from configurations involving no or one additional nucleon promoted from the sd to the fp shell agree relatively well with the energies of known states, while those that involve multi-particle excitations paint an interesting and complex picture of interplay between single-particle excitations, collective pairing, and deformation. This presents an interesting challenge for future theory.

Shapes, softness, and nonyrast collectivity in W186

Non-yrast, excited states in neutron-rich $^{186}$W were populated via inelastic-scattering reactions using beams of $^{136}$Xe nuclei accelerated to 725 and 800 MeV. Levels populated in the reactions were investigated via particle-$ \gamma $ coincidence techniques using the Gammasphere array of High-Purity Germanium detectors and the compact heavy-ion counter, CHICO2. The $ K^{\pi} = 2 ^{+} $ ($\gamma$), $ K^{\pi} = 0^{+}$ and $ K^{\pi} = 2^{-} $ (octupole) rotational side bands were extended to spins $ 14\hbar $, $ 12\hbar $, and $ 13\hbar $, respectively. A staggering pattern observed in the energies of levels in the $ K^{\pi} = 2^{+} $ band was found to be consistent with a potential that gets softer to vibration in the $ \gamma $ degree of freedom with increasing spin. The odd-even staggering of states in the $ K^{\pi} = 2^{-}$ band was found to exhibit a phase opposite to that seen in the $ \gamma $ band; an effect most probably associated with Coriolis coupling to other, unobserved octupole vibrational bands in $^{186}$W.

The muX project

The project is conducting a series of muonic X-ray measurements in medium- and high-Z nuclei at PSI, utilizing a high-purity germanium detector array, in-beam muon detectors, and a modern digital data-acquisition system. A novel hydrogen target for muon transfer was developed, enabling measurements with as little as a few micrograms of target material. First measurements with radioactive Cm and Ra targets were conducted, aimed at determining their nuclear charge radii. These serve as important input for upcoming atomic parity violation experiments. The apparatus is also used to perform a feasibility study of an atomic parity violation experiment with the 2s-1s2s−1s muonic X-ray transition. In addition, the setup has been made available for a wider range of nuclear, particle, and solid-state physics measurements.

Search for double- β decay of Ge76 to excited states of Se76 with the majorana demonstrator

The majorana demonstrator is a neutrinoless double-β decay search consisting of a low-background modular array of high-purity germanium detectors, ∼2/3 of which are enriched to 88% in Ge76. The experiment is also searching for double-beta decay of Ge76 to excited states (e.s.) in Se76. Ge76 can decay into three daughter states of Se76, with clear event signatures consisting of a ββ-decay followed by the prompt emission of one or two γ rays. This results with high probability in multi-detector coincidences. The granularity of the demonstrator detector array enables powerful discrimination of this event signature from backgrounds. Using 41.9 kg yr of isotopic exposure, the demonstrator has set world leading limits for each e.s. decay of Ge76, with 90% CL lower half-life limits in the range of (0.75–4.0)×1024 yr. In particular, for the 2ν transition to the first 0+ e.s. of Se76, a lower half-life limit of 7.5×1023 yr at 90% CL was achieved.4 MoreReceived 14 August 2020Accepted 2 November 2020DOI:https://doi.org/10.1103/PhysRevC.103.015501©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDouble beta decayNeutrinoless double beta decayProperties59 ≤ A ≤ 89TechniquesRadiation detectorsNuclear Physics

Confirming band assignments in 167ytterbium with gamma-gamma-electron triple-coincidence spectroscopy

Multipolarity measurements are presented for transitions in the deformed odd-mass nucleus 167 Yb in support of tentative spin assignments and level interpretations based upon the cranked-Nilsson model. Internal-conversion coefficients were measured with the SAGE (Silicon And GErmanium) spectrometer confirming several E2 transition assignments. The array of high-purity germanium detectors enabled the recording of high-multiplicity events from which $\gamma\gamma\gamma$ and $\gamma\gamma e^{-}$ data sets were extracted and the technique of high-fold $\gamma$-ray gating was demonstrated to cleanly isolate transitions of interest.

Low-spin excitations in Zr97

The main goal of this work is the determination of spins and parities of excited states in $^{97}\mathrm{Zr}$, among others the 2264.3-keV level, which had previously been tentatively reported as the $11/{2}^{\ensuremath{-}}$ excitation corresponding to the ${h}_{11/2}$ neutron orbital. Low-spin excited states in $^{97}\mathrm{Zr}$ were populated via the cold-neutron capture reaction. The $\ensuremath{\gamma}$ rays emitted following the reaction were measured using the highly efficient array of high-purity germanium detectors, EXILL, at the Institut-Laue-Langevin (ILL), Grenoble. The primary $\ensuremath{\gamma}$ rays deexciting the capture state in $^{97}\mathrm{Zr}$ were identified for the first time. The new, precise neutron binding energy in $^{97}\mathrm{Zr}$ of 5569.15(4) keV differs significantly from the value reported in the literature. The previously reported level scheme has been amended by several new low-spin levels. The ($n,\ensuremath{\gamma}$) data were complemented by a measurement of the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{97}\mathrm{Y}$ at the Lohengrin fission-fragment separator of the ILL, and the observation of the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{97}\mathrm{Y}$ populated in neutron-induced fission of $^{235}\mathrm{U}$ and measured using the EXILL Ge array. The combined data allowed unique spin-parity assignments for many levels in $^{97}\mathrm{Zr}$. The 2264.3-keV level, with a new spin-parity assignment of $9/{2}^{+}$, may correspond to the $\ensuremath{\nu}{g}_{9/2}$ extruder orbital.

Revalidation of the isobaric multiplet mass equation for theA=20quintet

An unexpected breakdown of the isobaric multiplet mass equation in the $A=20$, $T=2$ quintet was recently reported, presenting a challenge to modern theories of nuclear structure. In the present work, the excitation energy of the lowest $T = 2$ state in $^{20}$Na has been measured to be $6498.4 \pm 0.2_{\textrm{stat}} \pm 0.4_{\textrm{syst}}$ keV by using the superallowed $0^+ \rightarrow 0^+$ beta decay of $^{20}$Mg to access it and an array of high-purity germanium detectors to detect its $\gamma$-ray deexcitation. This value differs by 27 keV (1.9 standard deviations) from the recommended value of $6525 \pm 14$ keV and is a factor of 28 more precise. The isobaric multiplet mass equation is shown to be revalidated when the new value is adopted.

Performance of a compact multi-crystal high-purity germanium detector array for measuring coincident gamma-ray emissions

The Multi-sensor Airborne Radiation Survey (MARS) detector is a 14-crystal array of high-purity germanium (HPGe) detectors housed in a single cryostat. The array was used to measure the astrophysical S-factor for the 14N(p,γ)15O⁎ reaction for several transition energies at an effective center-of-mass energy of 163keV. Owing to the granular nature of the MARS detector, the effect of gamma-ray summing was greatly reduced in comparison to past experiments which utilized large, single-crystal detectors. The new S-factor values agree within their uncertainties with the past measurements. Details of the analysis and detector performance are presented.

Evaluation of internal occupational exposure by 123I in a radiopharmaceutical production facility

123I is a photon emitter radionuclide (159 keV) used for diagnostic procedures of endocrinal diseases in nuclear medicine. Since 1998 it is produced at the industrial radiopharmaceutical plant operated by the Institute for Nuclear Energy (IEN-CNEN) and supplied to clinics located in the State of Rio de Janeiro, in Brazil. The production of this radionuclide represents a risk of internal occupational exposure. According to international recommendations, workers involved in this activity should be routinely monitored in order to comply with dose limits and keep individual exposures as low and reasonably achievable. The Radiation Protection Plan implemented at the IEN includes annual in vivo measurements of 123I in the thyroid performed at the In Vivo Monitoring Laboratory of the Institute for Radiation Protection and Dosimetry (IRD-CNEN). This work describes a series of improvements on the measurement techniques used for the monitoring of the workers from the facility, including (i) optimization of in vivo measurement of the thyroid using an array of high-purity germanium detectors, (ii) development of a new in vitro bioassay method for the determination of 123I in urine samples using a HPGe germanium detector and (iii) the establishment of a methodology for internal dose assessment, based on bioassay data. The sensitivity of the methods allow detection of 123I activities below derived registry level of 1 mSv for the incorporation scenarios of exposure assumed in this work. Thus, it can be concluded that the methods are suitable for application in routine monitoring of workers occupationally exposed to 123I in this facility.

Quadrupole collectivity in neutron-rich Cd isotopes

The investigation of the excitation energies of the 2 1 + –states in the neutron-rich Cd isotopes shows an irregular behaviour when approaching the neutron shell-closure at N = 82. The energy of the 2 1 + –state in 128 Cd is lower than the one in 126 Cd. The transition strength B(E2, 0 gs + → 2 1 + ) in the even isotopes 122−128 Cd was measured in Coulomb excitation experiments with the high-purity germanium detector array MINIBALL at REXISOLDE (CERN). The values for 122,124 Cd coincide with beyond-mean-field calculations with a resultant prolate deformation, whereas 126,128 Cd are better described by shell-model calculations.

Measurement and analysis of gamma-rays emitted from spent nuclear fuel above 3 MeV

The gamma-ray spectrum of spent nuclear fuel in the 3–6MeV energy range is important for active interrogation since gamma rays emitted from nuclear decay are not expected to interfere with measurements in this energy region. There is, unfortunately, a dearth of empirical measurements from spent nuclear fuel in this region. This work is an initial attempt to partially fill this gap by presenting an analysis of gamma-ray spectra collected from a set of spent nuclear fuel sources using a high-purity germanium detector array. This multi-crystal array possesses a large collection volume, providing high energy resolution up to 16MeV. The results of these measurements establish the continuum count-rate in the energy region between 3 and 6MeV. Also assessed is the potential for peaks from passive emissions to interfere with peak measurements resulting from active interrogation delayed emissions. As one of the first documented empirical measurements of passive emissions from spent fuel for energies above 3MeV, this work provides a foundation for active interrogation model validation and detector development.

Detection Efficiency for Measuring 241Am in Axillary Lymph Nodes Using Different Types and Sizes of Detectors

The detection efficiency and interference susceptibility of four different types of low energy photon detectors, each with a unique geometric arrangement, were compared for direct measurement of Am deposited in the axillary lymph nodes. Although the most efficient detector was a single large 23,226 mm square phoswich detector, it was also the most susceptible to confounding depositions from activity deposited in adjacent organs. The array of two 2,800 mm high purity germanium detectors exhibited the highest efficiency per unit detector area with some resistance to confounding from activity deposited in the lungs. The array of two 4,560 mm NaI(Tl) detectors was the least susceptible to confounding and nearly as efficient per square millimeter as the high purity germanium detector array. Thus, selection of a detector system for in vivo measurement of activity deposited in the axillary lymph nodes should consider whether there is a likelihood for activity deposited in other organs, such as the lungs, skeleton, or liver, to create an interference that will confound the measurement result.

Monte Carlo simulation of embedded 241Am activity in injured palm

This paper describes a methodology to estimate embedded activity of (241)Am and Pu isotopes in a wound at an unknown depth. Theoretical calibration of an array of high-purity germanium detectors is carried out using the Monte Carlo code 'FLUKA' for a (241)Am source embedded at different depths in a soft tissue phantom of dimension 10 × 10 × 4 cm(3) simulating the palm of a worker. It is observed that, in the case of contamination due to pure (241)Am, the ratio of counts in 59.5 and 17.8 keV (Ratio 1) should be used to evaluate the depth, whereas the ratio of counts in 59.5 and 26.3 keV (Ratio 2) should be used when the contamination is due to a mixture of Pu and (241)Am compounds. Variations in the calibration factors (CFs) as well as in the Ratio 1 and Ratio 2 values are insignificant when source dimensions are varied from a point source to a 15-mm diameter circle. It is observed that tissue-equivalent polymethyl methacrylate material can be used in the phantom to estimate the embedded activity, when the activity is located at a depth of <1 cm, as the corresponding CFs do not show much variation with respect to those estimated using the phantom containing soft tissue material. In all other cases, an appropriate soft tissue-equivalent material should be used in the phantom for the estimation of CFs and ratios. The CFs thus obtained will be helpful in an accurate estimation of the depth of the wound and the activity embedded therein in the palm of a radiation worker.

Off-line data quality monitoring for the GERDA experiment

Gerda is an experiment searching for the neutrinoless ββ decay of 76Ge. The experiment uses an array of high-purity germanium detectors, enriched in 76Ge, directly immersed in liquid argon. Gerda recently started the physics data taking using eight enriched coaxial detectors. The status of the experiment has to be closely monitored in order to promptly identify possible instabilities or problems. The on-line slow control system is complemented by a regular off-line monitoring of data quality. This ensures that data are qualified to be used in the physics analysis and allows to reject data sets which do not meet the minimum quality standards. The off-line data monitoring is entirely performed within the software framework Gelatio. In addition, a relational database, complemented by a web-based interface, was developed to support the off-line monitoring and to automatically provide information to daily assess data quality. The concept and the performance of the off-line monitoring tools were tested and validated during the one-year commissioning phase.

Off-line data processing and analysis for the GERDA experiment

Gerda is an experiment designed to look for the neutrinoless double beta decay of 76Ge. The experiment uses an array of high-purity germanium detectors (enriched in 76Ge) directly immersed in liquid argon. Gerda is presently operating eight enriched coaxial detectors (approximately 15 kg of 76Ge) and about 25 new custom-made enriched BEGe detectors will be deployed in the next phase (additional 20kg of 76Ge). The paper describes the Gerda off-line analysis of the high-purity germanium detector data. Firstly we present the signal processing flow, focusing on the digital filters and on the algorithms used. Secondly we discuss the rejection of non-physical events and the data quality monitoring. The analysis is performed completely with the Gerda software framework (Gelatio), designed to support a multi-channel processing and to perform a modular analysis of digital signals.

Lung counting: comparison of detector performance with a four detector array that has either metal or carbon fibre end caps, and the effect on mda calculation

This study described the performance of an array of high-purity Germanium detectors, designed with two different end cap materials-steel and carbon fibre. The advantages and disadvantages of using this detector type in the estimation of the minimum detectable activity (MDA) for different energy peaks of isotope (152)Eu were illustrated. A Monte Carlo model was developed to study the detection efficiency for the detector array. A voxelised Lawrence Livermore torso phantom, equipped with lung, chest plates and overlay plates, was used to mimic a typical lung counting protocol with the array of detectors. The lung of the phantom simulated the volumetric source organ. A significantly low MDA was estimated for energy peaks at 40 keV and at a chest wall thickness of 6.64 cm.

Re-evaluating reaction rates relevant to nova nucleosynthesis from a nuclear structure perspective

Conventionally, reaction rates relevant to nova nucleosynthesis are determined by performing the relevant proton capture reactions directly for stable species, or as has become possible more recently in inverse kinematics using short-lived accelerated radioactive beams with recoil separators. A secondary approach is to compile information on the properties of levels in the Gamow window using transfer reactions. We present a complementary technique where the states of interest are populated in a heavy-ion fusion reaction and their gamma decay studied with a state-of-the-art array of high-purity germanium detectors. The advantages of this approach, including the ability to determine resonance energies with high precision and the possibility of determining spins and parities from gamma-ray angular distributions are discussed. Two specific examples related to the 22Na(p, γ) and 30P(p, γ) reactions are presented.