Array Of HPGe Detectors Research Articles

Development of a charged particle-[formula omitted] coincidence system for nuclear structure and reaction studies at TIFR

A new detector system for measurements of charged particles and γ-rays in coincidence has been developed at TIFR Mumbai, by coupling an annular double-sided segmented Si detector with an array of Compton-suppressed clover HPGe detectors. Digital data acquisition system has been configured for the setup, which has been calibrated and tested using the 229Th radioactive source that emits α-particles along with γ-rays. The functionality and performance of the coincidence apparatus for Doppler correction of γ-transitions emitted during the in-flight de-excitation of the projectile and the target in the 30Si + 197Au Coulomb excitation experiment have been demonstrated.

Laboratory magnetoplasmas as an ideal experimental environment for nuclear astrophysics β-decay studies

The PANDORA project proposes a new experimental approach aimed at using laboratory magnetoplasmas (which emulate some stellar conditions) as an environment for in-plasma β-decays investigations. In the superconducting PANDORA trap, a hot plasma containing a known concentration of β-decaying atoms can be confined and kept in dynamic equilibrium for weeks. The decay rate can be measured by detecting the γ-rays emitted by the daughter nuclei (through HPGe detector array) and correlated with the charge state distribution of radioactive ions and with the plasma thermodynamic properties using a multi-diagnostic system, whose tools and techniques are here presented.

Precision measurements of the 12C(αγ) reaction with gamma beams and TPC detector(s)

The cross section of the 12C(α,γ)16O reaction, well-recognized as the most important nuclear input of stellar evolution theory, has eluded precise measurements over the last few decades, as evident in the lack of precise confirmation of an elementary prediction of quantum mechanics of the E1-E2 mixing phase angle (ϕ12). More troubling are modern data, measured with 4π array of HPGe detectors, that are in conflict with this prediction. A new method to measure this cross section with TPC detectors and gamma-beams, by measuring the time reverse 16O(γ,α)12C reaction discussed here, shows great promise, for example the measured data do not disagree with the predicted π12 and agree with the predicted trend.

Design study of a HPGe detector array for β-decay investigation in laboratory ECR plasmas

In the frame of the PANDORA project, a new experimental approach aims at measuring in-plasma β-decay rate as a function of thermodynamical conditions of the environment, namely a laboratory magnetized plasma able to mimic some stellar-like conditions. The decay rates (expected to change dramatically as a function of the ionization state) will be measured as a function of the charge state distribution of the in-plasma ions. The new experimental approach aims at correlating the plasma environment and the decay rate. This can be performed by simultaneously identifying and discriminating—through an innovative multi-diagnostic system working synergically with a γ-ray detection system —the photons emitted by the plasma and γ-rays emitted after the isotope β-decay. In this study, the numerical simulations supporting the design of the γ-ray detector array, including a statistical significance study to check the feasibility of measuring the in-plasma decay rates, are presented. Geant4 simulations focused on the design of the array of γ-ray detectors and the evaluation of total efficiency depending on the detector type and the optimal displacement of detectors around the trap (including collimation systems and shielding). The simulation results showed that, due to technical limitations in the number of apertures that can be created in the magnetic trap, the best compromise is to use 14 HPGe (70% of relative efficiency) detectors surrounding the magnetic trap. The HPGe detectors were chosen for their excellent energy resolution (0.2% @ 1 MeV), since the harsh environment (the background is represented by the intense plasma self-emission) strongly affects the signal-to-background ratio. Once determined the total photopeak efficiency (0.1–0.2%), the sensitivity of the PANDORA experiment was checked in a “virtual experimental run,” by exploring the measurability of isotope decay rates for the first three physical cases of PANDORA: 176Lu, 134Cs and 94Nb. The preliminary results demonstrated the feasibility of the measurement in terms of the signal-to-background ratio and significance that it is possible to reach. The results indicated that experimental run durations could take from several days to 3 months, depending on the isotope under investigation, thus shedding new light on the role of weak interactions in stellar nucleosynthesis.

Optimization of FLUKA detector model for HPGe array

Monte Carlo codes, such as FLUKA, are widely used to optimize calibration of spectrometric systems. HPGe detector array (HDA) for lung monitoring was modeled in FLUKA code using available information about their geometry and optimized for efficiency using 241Am point source at smaller distances (<10 cm) as in case of in-vivo monitoring scenarios. Thickness of dead layer (DL) on the top and lateral detector surfaces for low energy counting was determined by considering the experimental and simulated efficiency for various energies. Using trial and error method, optimized DL thickness was found out to be 2.5 μm on top surface and 1.8 mm on lateral surfaces for each HPGe detector in the array. For the optimized model, it was found that the simulated and experimental efficiency and the simulated and experimental spectra were in reasonable agreement. Optimization of the HDA was an important benchmarking step to reduce the simulation errors before they are implemented in complex numerical problems using computational phantoms.

Low-spin particle-core and hole-core excitations in Ca41,47,49 isotopes studied by cold-neutron-capture reactions

We present recent results on the structure of the one-valence-particle $^{41}$Ca and $^{49}$Ca, and one-valence-hole $^{47}$Ca, nuclei. The isotopes of interest were populated via the cold-neutron capture reactions $^{40}$Ca(n,$\gamma$), $^{48}$Ca(n,$\gamma$) and $^{46}$Ca(n,$\gamma$), respectively. The experiments were performed at the Institut Laue-Langevin, within the EXILL campaign, which employed a large array of HPGe detectors. The $\gamma$ decay and level schemes of these nuclei were investigated by $\gamma$-ray coincidence relationships, leading to the identification of 41, 10, and 6 new transitions in $^{41}$Ca, $^{47}$Ca, and $^{49}$Ca, respectively. Branching ratios and intensities were extracted for the $\gamma$ decay from each state, and $\gamma$-ray angular correlations were performed to establish a number of transition multipolarities and mixing ratios, thus helping in the spin assignment of the states. The experimental findings are discussed along with microscopic, self-consistent beyond-mean-field calculations performed with the Hybrid Configuration Mixing model, based on a Skyrme SkX Hamiltonian. The latter suggests that a fraction of the low-spin states of the $^{41}$Ca, $^{49}$Ca, and $^{47}$Ca nuclei is characterized by the coexistence of either 2p-1h and 1p-2h excitations, or couplings between single-particle/hole degrees of freedom and collective vibrations (phonons) of the doubly-magic "core".

Intrinsic electric quadrupole moment of the Kπ=8− isomeric state in Hf178

The lifetime of the ${9}^{\ensuremath{-}}$ state in the rotational band based on the 4.0 s, ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$, isomeric state ($^{178}\mathrm{Hf}^{{m}_{1}}$) from the decay of the 31-yr isomer ($^{178}\mathrm{Hf}^{{m}_{2}}$) was determined to be 99(2) ps by means of the fast-timing technique using two ${\mathrm{LaBr}}_{3}$(Ce) scintillators. The $\ensuremath{\delta}(E2/M1)$ mixing ratios of the $\mathrm{\ensuremath{\Delta}}I=1\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ rays depopulating levels in this band were deduced from $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ angular correlations by using a $^{178}\mathrm{Hf}^{{m}_{2}}$ radioactive source located at the center of the Gammasphere HPGe detector array. The new results, together with previous spectroscopic information, provide a different way to extract the intrinsic quadrupole moment of ${Q}_{0}=6.45(14)\phantom{\rule{4pt}{0ex}}e\text{b}$ for the $^{178}\mathrm{Hf}^{{m}_{1}}$ band. A possible explanation for the reduction of the $^{178}\mathrm{Hf}^{{m}_{1}}$ nuclear charge radius is presented.

Efficient determination of HPGe [formula omitted]-ray efficiencies at high energies with ready-to-use simulation software

The full-energy-peak efficiency of HPGe detectors at γ-ray energies around 10MeV is not easily accessible with experimental methods. Monte-Carlo simulations with Geant4 can provide these efficiencies. G4Horus is a ready-to-use Geant4 application for the HORUS HPGe-detector array. Users can configure the modular parts to match their experiment with minimal knowledge of the simulation software and limited time commitment. In our case, knowing and implementing the geometry with high precision is the biggest challenge. To implement the different target chambers, we transform the existing CAD models to Geant4 geometry with CADMesh. We also found a large discrepancy between experimental and simulated efficiency for some older HPGe detectors, which could be remedied by introducing a large dead region around the inner core. This project is open source and available from https://github.com/janmayer/G4Horus (Mayer 2020). We invite everyone to adapt the project or adopt parts of the code for other projects.

Post-upgrade performance of GERDA Phase II

Excellent spectroscopic performance, event topology information and outstanding radiopurity are unique properties of HPGe detectors that facilitate the search for 0vββ decay of 76Ge. A detection of this process would shed light onto physics beyond the standard model, as it would uncover the Majorana nature of neutrinos. The GERDA experiment employs an array of HPGe detectors, made from isotopically modified material, in an active liquid argon shield at the LNGS underground laboratory. The combination of an ultra-low background environment with active background rejection techniques allows the exploration of 0vββ decay half-lives beyond 1026 yr. No signal has been found in the first 58.9 kg⋅yr of Phase II data, from which the most stringent limit on 0vββ decay of 76Ge has been derived. In the course of an upgrade new HPGe detectors of novel type have been added to the array, increasing the total mass of enriched germanium to 44.2 kg. More than one year of data has been collected in this configuration. The first 24.9 kg⋅yr reveal encouraging performance for the ongoing 0vββ decay search.

Measurement of Gamma-Ray from Inelastic Neutron Scattering on 56Fe

In nuclear reactors, inelastic neutron scattering is a significant energy-loss mechanism which has deep impacts on designments of nuclear reactor and radiation shielding. Iron is an important material in reactor. However, for the existing nuclear data for iron, there exists an obvious divergence for the inelastic scattering cross sections and the related gamma production sections. Therefore the precise measurements are urgently needed for satisfying the demanding to design new nuclear reactors (fast reactors), Accelerator Driven Subcritical System (ADS), and other nuclear apparatus. In this paper, we report a new system with an array of HPGe detectors, electronics and acquisition system. Experiments had been carried out on three neutron facilities.

Identification of different reaction channels in 6Li + 89Y experiment by the particles-γ coincidence measurement

This short paper presents the investigation of reaction mechanism induced by 6Li through a particle­γ coincidence measurement. The data have been taken from a 6Li+89Y experimentwhich is performed inINFN-LNL, Italy. In this experiment, the light charged particles are detected by a Si­ball, named EUCLIDES, and the γ rays are collected by a HPGe detector array, called GALILEO. In this contribution, scientific motivations, experimental details and some results, such as α­γ analysis, are presented.

The γ-γ fast-timing technique and the EXILL&FATIMA campaign

At the Institut Laue-Langevin in Grenoble, germanium-gated γ-γ fast-timing lifetime measurements of nuclear excited states in neutron-rich nuclei have been performed within a prompt γ-ray spectroscopy experimental campaign. We report on results obtained from the cold-neutron induced fission of 235U. The excited secondary fission products were stopped almost instantaneously within the thick target and the γ rays emitted were collected triggerlessly using the EXILL&FATIMA mixed array of HPGe and LaBr3(Ce) detectors. Precise lifetimes could be determined by analysing the γ-γ time difference spectra using the generalized centroid difference method. This picosecondsensitive method provides many advantages and is briefly explained. Still, the major source of systematic errors is related to the contribution of time-correlated Compton background. The EXILL&FATIMA results are discussed with respect to the typical energy-dependent timing behaviour of the background. According to the time response of the background, appropriate methods and a time correction for the sub-nanosecond regime are proposed.

(n,γ) reactions on rare Ca isotopes: Valence-hole - core excitation couplings in 47Ca

Recent results on the structure of 47Ca will be presented. The nucleus of interest was populated via the cold-neutron capture 46Ca(n,γ) reaction, on a rare 46Ca target, during the EXILL experimental campaign at the nuclear reactor of Institut Laue- Langevin in Grenoble. High-resolution γ-ray spectroscopy, performed with a composite array of HPGe detectors, enabled the identification of new transitions deexciting states between the neutron-capture level and the ground state. Experimental data will be compared with a novel microscopic theoretical model, currently under development, specifically designed to describe the low-lying structure of odd-mass nuclei with one valence particle/hole outside a spherical doubly-magic core, using the Skyrme effective interaction self-consistently.

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Background: In the neutron-rich $A\ensuremath{\approx}100$ mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change.Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass $A=100$ up to mass $A=108$, and the results that were obtained.Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the $\ensuremath{\gamma}$ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a $\ensuremath{\gamma}$-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps.Results: Even-even molybdenum isotopes from mass $A=100$ to $A=108$ were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: $\ensuremath{\tau}=29.{7}_{\ensuremath{-}9.1}^{+11.3}$ ps for the ${4}^{+}$ state of $^{108}\mathrm{Mo}$ and $\ensuremath{\tau}=3.{2}_{\ensuremath{-}0.7}^{+0.7}$ ps for the ${6}^{+}$ state of $^{102}\mathrm{Mo}$.Conclusions: The reduced transition strengths $B(E2)$, calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from $A=100$ to $A=108$ with a maximum reached at $N=64$. The transition probabilities decrease for $^{108}\mathrm{Mo}$ which may be related to its well-pronounced triaxial shape indicated by the calculations.

Status of the MAJORANA DEMONSTRATOR

The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44-kg (29 kg 76Ge and 15 kg natGe) to search for neutrinoless double beta decay in Ge-76. The next generation of tonne-scale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstrate a path forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. The MAJORANA DEMONSTRATOR follows a modular implementation to be easily scalable to the next generation experiment. First, the prototype module was assembled; it has been continuously taking data from July 2014 to June 2015. Second, Module 1 with more than half of the total enriched detectors and some natural detectors has been assembled and it is being commissioned. Finally, the assembly of Module 2, which will complete MAJORANA DEMONSTRATOR, is already in progress.

Inelastic neutron scattering with GAINS at GELINA: An overview of the last decade

GAINS is an array of HPGe detectors installed at the GELINA neutron source of Joint Research Center, Geel, Belgium. It served to measure the cross section for (n,n’γ) reactions on many isotopes. The paper presents the experimental setup and reviews the main results obtained in the last decade

METHODOLOGY FOR THE ASSESSMENT OF INGESTED ACTINIDES FROM MONTE CARLO SIMULATION OF VOXEL PHANTOM

In case of internal contamination of actinides by ingestion pathway, activity will be transferred to various regions of the alimentary tract over a period of time. In this article, counting efficiencies (CEs) of Phoswich and an array of HPGe detectors are estimated for source in alimentary tract of voxel phantom. The phantom as well as Phoswich, and an array of three HPGe detectors are incorporated in Monte Carlo code 'FLUKA'. Human alimentary tract model is solved using default parameters to identify different compartments where activity will accumulate after an ingestion intake of 1 Bq as a function of time. Accordingly, CEs are evaluated on 0.5-5 d post ingestion intake for the source distributed in the contents of alimentary tract for photon energies in 18-238 keV range representing sources of actinides. The assessment of ingested activity of actinides from abdomen measurements is discussed. Higher CEs are observed with Phoswich detector compared with HPGe array due to its large size and high effective Z. Also, the CEs observed on Days 1-5 using both the detectors are found to decrease by 16-75 % with respect to the CE on half day. Thus, there is need to use CEs according to the observed activity distribution post ingestion intake. The contribution in the abdomen measurements due to source in the lungs and vice versa is also studied for intake by both inhalation and ingestion pathways. The contribution of source in the liver is found to be ∼30-50 % in chest and 75 % in abdomen measurements.

Search for E1 strength in 62,64Fe around the threshold

The structure and nature of the pygmy dipole resonance (PDR) states below and above the neutron threshold is a recent open problem, particularly in exotic, neutron rich nuclei. Present experimental observations give only limited information on this subject. New experiments using different methods are needed. A recent measurement at the GSI laboratories on 62,64Fe with the PRESPEC (2014) setup, following a past experiment with the RISING (2005) setup on 68Ni, will contribute to solve the open questions. The setup located at GSI consists of the segmented HPGe detector array AGATA, scintillators (HECTOR), an Energy Loss / Total Energy time of flight measuring detector system called LYCCA and the fragment separator (FRS) apparatus. The experiment is based on relativistic Coulomb excitation together with the detection of the incoming and outgoing particles event by event. The detection of the produced y-rays in the reactions, provides insight into the problem of the electric dipole response and E1 strength distribution around particle separation threshold.

Assessment of uncertainties in the lung activity measurement of low-energy photon emitters using Monte Carlo simulation of ICRP male thorax voxel phantom.

Assessment of intake due to long-lived actinides by inhalation pathway is carried out by lung monitoring of the radiation workers inside totally shielded steel room using sensitive detection systems such as Phoswich and an array of HPGe detectors. In this paper, uncertainties in the lung activity estimation due to positional errors, chest wall thickness (CWT) and detector background variation are evaluated. First, calibration factors (CFs) of Phoswich and an array of three HPGe detectors are estimated by incorporating ICRP male thorax voxel phantom and detectors in Monte Carlo code 'FLUKA'. CFs are estimated for the uniform source distribution in lungs of the phantom for various photon energies. The variation in the CFs for positional errors of ±0.5, 1 and 1.5 cm in horizontal and vertical direction along the chest are studied. The positional errors are also evaluated by resizing the voxel phantom. Combined uncertainties are estimated at different energies using the uncertainties due to CWT, detector positioning, detector background variation of an uncontaminated adult person and counting statistics in the form of scattering factors (SFs). SFs are found to decrease with increase in energy. With HPGe array, highest SF of 1.84 is found at 18 keV. It reduces to 1.36 at 238 keV.

High-resolution two-proton stripping to 2p-1h 7/2- states via the 59Co(3He,n $\gamma$ )61Cu reaction

The challenge of achieving high resolution in binary reactions involving an outgoing high-energy neutron is solved by detecting the \( \gamma\)-ray decay of populated excited states in an array of escape-suppressed HPGe detectors in coincidence with fast neutrons. The selectivity of the arrangement is of the order of 1 in 1000 and is demonstrated by L = 0 two-proton stripping to 7/2- 2p-1h levels using the 59Co(3He,\(n \gamma\))61Cu reaction at Elab = 22.5 MeV. The observed relative two-proton stripping strengths are compared with large-basis shell-model calculations.