Ge Detector Research Articles

Half-life of the15/2+state ofI135: A test ofE2seniority relations

The half-life of the 15/21+ state of the 3-valence-proton nucleus I135 has been measured to be 1.74(8) ns using the EXILL-FATIMA mixed array of Ge and LaBr3 detectors. The nuclei were produced following the cold neutron-induced fission of a U235 target at the PF1B beam line of the Institut Laue-Langevin. The extracted B(E2;15/2+→11/2+) value enabled a test of seniority relations for the first time between E2 transition rates. Large-scale shell-model calculations were performed for Te134 and I135, and reinterpreted in a single-orbit approach. The results show that the two-body component of the E2 operator can be large whereas energy shifts due to the three-body component of the effective interaction are small.Received 23 November 2016Revised 20 January 2017Corrected 22 February 2017DOI:https://doi.org/10.1103/PhysRevC.95.021302©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsNuclear structure & decaysNuclear Physics

Toward single electron resolution phonon mediated ionization detectors

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14eVee. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5GeV/c2 but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7eVee for 0.25kg (d=75mm, h=1cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25mm) will reach a resolution of ∼2.8eVee. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

Measurements of radon activity concentration in mouse tissues and organs.

The purpose of this study is to investigate the biokinetics of inhaled radon, radon activity concentrations in mouse tissues and organs were determined after mice had been exposed to about 1MBq/m3 of radon in air. Radon activity concentrations in mouse blood and in other tissues and organs were measured with a liquid scintillation counter and with a well-type HP Ge detector, respectively. Radon activity concentration in mouse blood was 0.410 ± 0.016Bq/g when saturated with 1MBq/m3 of radon activity concentration in air. In addition, average partition coefficients obtained were 0.74 ± 0.19 for liver, 0.46 ± 0.13 for muscle, 9.09 ± 0.49 for adipose tissue, and 0.22 ± 0.04 for other organs. With these results, a value of 0.414 for the blood-to-air partition coefficient was calculated by means of our physiologically based pharmacokinetic model. The time variation of radon activity concentration in mouse blood during exposure to radon was also calculated. All results are compared in detail with those found in the literature.

Monte Carlo simulation of background characteristics of a HPGe detector operating underground in the Gran Sasso National Laboratory

Monte Carlo (MC) simulation of background components of an ultra-low background high purity germanium (HPGe) detector operating in a deep underground laboratory was carried out. The results show that the background of the HPGe detector is about two orders of magnitude higher than the MC prediction when accounting only for cosmic-ray induced background. The difference is due to natural radioactivity in the parts surrounding the Ge detector. To get reasonable agreement between MC simulations and the experiment, a contamination in the parts surrounding the Ge crystal from 40K, 208Tl and 214Bi of 0.1mBqkg−1 was required to include in the simulations.

Theoretical and experimental study of the electronic states and spectra of KBi and KSb

Gas phase emission spectra of the hitherto unknown free radicals KBi and KSb were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth or antimony vapor in argon carrier gas was passed through a microwave discharge and mixed with potassium vapor in an observation tube. For KBi, two systems of blue-degraded bands observed in the range 5800–7700cm−1 are assigned to the transitions A3Π (A20+)→X3Σ−(X10+, X21). Nine bands of the A20+→X10+ and three bands of the A20+→X21 system were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses yielded the spectroscopic parameters of the X10+, X21, and A20+ states. For KSb, in the range of the sensitive Ge detector, only one sequence of bands was measured near 6880cm−1. By analogy with the previously observed spectra of NaSb and NaAs these bands were identified to be the Δv=0 sequence of the a2→X21 transition of KSb. Some very weak bands observed at low resolution in the range 3800–5200cm−1 are assigned to the transitions A3Π (A21)→X3Σ −(X10+, X21).To aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential energy curves for the low-lying states of KBi and KSb, vibrational constants, equilibrium internuclear distances, and also electric dipole transition moments connecting the states.

Measurement of aluminum activation cross section and gas production cross section for 0.4 and 3-GeV protons

To estimate the lifetime and the radiation dose of the proton beam window used in the spallation neutron source at J-PARC, it is necessary to understand the accuracy of the production cross section of 3-GeV protons. To obtain data on aluminum, the reaction cross section of aluminum was measured at the entrance of the beam dump placed in the 3-GeV proton synchrotron. Owing to the use of well-calibrated current transformers and a well-collimated beam, the present data has good accuracy. After irradiation, the cross sections of Al(p,x)7 Be, Al(p,x)22 Na-22 and Al(p,x)24 Na were obtained by gamma-ray spectroscopy using a Ge detector. It was found that the evaluated data of JENDL/HE-2007 agree well with the current experimental data, whereas intra-nuclear cascade models (Bertini, INCL-4.6, and JAM) with the GEM statistical decay model underestimate by about 30% in general. Moreover, gas production, such as T and He, and the cross sections were measured for carbon, which was utilized as the muon production target in J-PARC. The experiment was performed with 3-GeV proton having beam power of 0.5 MW, and the gasses emitted in the process were observed using a quadrupole mass spectrometer in the vacuum line for beam transport to the mercury target. It was found that the JENDL/HE-2007 data agree well with the present experimental data.

COHERENT Experiment: current status

The COHERENT Collaboration is realizing a long term neutrino physics research program. The main goals of the program are to detect and study elastic neutrino-nucleus scattering (CEνNS). This process is predicted by Standard Model but it has never been observed experimentally because of the very low energy of the recoil nucleus. COHERENT is using different detector technologies: CsI[Na] and NaI scintillator crystals, a single-phase liquid Ar and a Ge detectors. The placement of all the detector setups is in the basement of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The current status of the COHERENT experimental program is presented.

Determination of activity of 51Cr on gamma radiation measurements

A method of determining the activity of intensive distributed -sources on the measurement of the continuous spectrum of radiation, for example the internal bremsstrahlung, is developed. The recurrent formula for reconstructing of a continuous spectrum, registered in a Ge detector, at distorting it in the detector. The method of precise measurements of the spectrum of 51Cr internal bremsstrahlung using two point sources of low activity is described.

Experimental programme on absolute fission fragment yields with the lohengrin spectrometer: New optical and statistical methodologies

The study of fission yields has a major impact on the characterization and understanding of the fission process and is mandatory for reactor applications. The mass and isotopic yields of the fission fragments have a direct influence on the amount of neutron poisons that limit the fuel burnup and on the evaluation of the residual power of the reactor after shutdown. The fission yields of the plutonium nuclides are also mandatory for the studies on the fuel multi-recycling. In order to significantly improve the precision of nuclear data, more and more fundamental fission models are used in the evaluation processing. Therefore, tests of fission models become a central issue to achieve a coherent libraries of nuclear data. In this framework, an important investigation in the experimental limits of facilities is required to provide complete sets of data with their coherent variance-covariance matrices. In the past with the LOHENGRIN spectrometer of the ILL, priority has been given for the studies in the light fission fragment mass range. The LPSC in collaboration with ILL and CEA has developed a measurement program on symmetric and heavy mass fission fragment distributions. The combination of measurements with ionisation chamber and Ge detectors is necessary to describe precisely the heavy fission fragment region in mass and charge. Recently, new measurements of fission yields and kinetic energy distributions, with different fissioning systems, were performed with this facility. The focus has been done on the selfnormalization of the data to provide new absolute measurements, independently of any libraries, and the experimental covariance matrix. To reach precise measurements, a new experimental procedure was developed along with a new analysis method based on metadata. Because of the complex correction scheme from count rates to yields, a classical propagation uncertainty is not possible. The new analysis path gives the mean value of mass yields, its probability density function and the associated experimental variance-covariance matrices. All this information is a first step to bring nuclear data into statistical tests of the underlying hypothesis of fission models.

Measurement of activation of helium gas by238U beam irradiation at about 11 A MeV

A new helium-gas stripper system has been applied at the ~11 A MeV uranium beam of the Radioactive Isotope Beam Factory of the RIKEN accelerator facility. Although the gas stripper is important for the heavy-ion accelerator facility, the residual radiation that is generated is a serious problem for maintenance work. The residual dose was evaluated by using three-layered activation samples of aluminium and bismuth. The γ-rays from produced radionuclides with in-flight fission of the 238 U beam and from the material of the chamber activated by neutrons were observed by using a Ge detector and compared with the values calculated by using the Monte-Carlo simulation code PHITS.

Status of the MAJORANA DEMONSTRATOR

The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultralow background, 40-kg modular high purity Ge (HPGe) detector array to search for neutrinoless double-beta decay (0νββ-decay) in 76Ge. The goal of the experiment is to demonstrate a background rate at or below 3 counts/(t-y) in the 4 keV region of interest (ROI) around the 2039 keV Q-value for 76Ge 0νββ-decay. In this paper, the status of the MAJORANA DEMONSTRATOR, including its design and measurements of properties of the HPGe crystals is presented.

Apparatus complex based on liquid xenon detector for gamma spectrometry in the intervals between pulses of intense radiation

To investigate the effects of intense radiation on the operation of the liquid xenon spectrometer we have created apparatus complex on the basis of the liquid xenon detector. The experimental setup consists of a multifunctional chamber, gas system, cooling system, temperature control system, X-ray generator, a special preamp, passive protection, scintillation monitor of the accelerator beam, thermoluminescent dosimeters, copper monitor bremsstrahlung, Ge(Li) detector. Multifunctional chamber includes a detecting unit (flat or cylindrical ionization chamber), the cleaning unit of the xenon, control unit of the purity of liquid xenon. The liquid xenon detector was irradiated by bremsstrahlung pulses of the microtron. The frequency of irradiation pulses was 400 Hz. The absorbed dose was varied from 10-7 to 0.1 Gy per pulse. The electronic and ionic processes in liquid xenon at different radiation doses were investigated. The recovery time of the spectrometric mode of operation of the liquid xenon detector after intense pulse irradiation has been studied. Stable operation of the liquid xenon spectrometer in the intervals between the pulses of the accelerator shown for a long time.

Developments of a new data acquisition system at ANNRI

A new data acquisition system (DAQ system) has been developed at the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) facility in the Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility (J-PARC/MLF). DAQ systems for both the Ge detector system and the Li-glass detector system were tested by using a gold sample. The applicability of the time-of-flight method was checked. System performance was evaluated on the basis of digital conversion nonlinearity, energy resolution, multi-channel coincidence and dead time.

Nondestructive Determination of 235U Enrichment of Uranium Samples in the Presence of Actinides (232Th, 236U, 237Np)

The measurements were performed using a planar Ge detector. The multi-group analysis (MGA) for the determination isotopic abundances in low enriched uranium samples is applied in this study. In order to perform the analysis of complex gamma-spectrums, were taken a number of gamma-spectrums of single reference samples, containing 235U, 238U, 232Th, 236U, 237Np with declared isotopic abundance. The gamma-ray spectrums in the range of low energy X-ray and gamma-ray peaks of these samples were obtained and analyzed.

Study of fission fragment de-excitation by gamma-ray spectrometry with the EXILL experiment

A large array of Ge detectors installed at ILL, around a 235 U target irradiated with cold neutrons, (EXILL) allowed measurement of prompt gamma-ray cascades occurring in fission fragments with an unambiguous determination of fragments. Here we present preliminary results of a systematic comparison between experimental γ-ray intensities and those obtained from the Monte-Carlo simulation code FIFRELIN, which is dedicated to the de-excitation of fission fragments. Major γ-ray intensities in the 142 Ba and 92 Kr fission products, extracted from EXILL data, were compared to FIFRELIN, as well as to reported values (when available) obtained with EUROGAM2 in the spontaneous fission of 248 Cm. The evolution of γ-ray intensities in 92 Kr versus the complementary partner in fission (i.e. versus the total number of evaporated neutrons by the fission pair) was then extracted and compared to FIFRELIN.

Thick target yields of proton induced gamma-ray emission from Al, Si and P

Thick target excitation yield curves of gamma-rays from the reactions 27Al(p,p′γ)27Al (Eγ=844 and 1014keV), 27Al(p,αγ)27Al (Eγ=1369keV), 28Si(p,p′γ)28Si (Eγ=1779keV), 29Si(p,p′γ)29Si (Eγ=1273keV) and 31P(p,p′γ)31P (Eγ=1266keV) were measured by bombarding pure-element targets with protons at energies below 3MeV. Gamma-rays were detected with a High Purity Ge detector placed at an angle of 90° with respect to the beam direction. The obtained thick target gamma-ray yields were compared with the previously published data. The overall systematic uncertainty of the thick target yield values was estimated to be better than ±9%.

Investigation of cosmic-ray induced background of Germanium gamma spectrometer using GEANT4 simulation

In this article, a GEANT4 Monte Carlo simulation toolkit was used to study the response of the cosmic-ray induced background on a High-Purity Germanium (HPGe) gamma spectrometer in the wide energy range, up to 100MeV. The natural radiation background measurements of the spectrometer were carried out in the energy region from 0.04 to 50MeV. The simulated cosmic-ray induced background of the Ge detector was evaluated in comparison with the measured data. The contribution of various cosmic-ray components including muons, neutrons, protons, electrons, positrons and photons was investigated. We also analyzed secondary particle showers induced by the muonic component.

Sensitivity to oscillation with a sterile fourth generation neutrino from ultralow threshold neutrino-nucleus coherent scattering

We discuss prospects for probing short-range sterile neutrino oscillation using neutrino-nucleus coherent scattering with ultra-low energy ($\sim 10$ eV - 100 eV) recoil threshold cryogenic Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A\&M University, and references developing technology based upon economical and scalable detector arrays. The baseline of the experiment is substantially shorter than existing measurements, as near as about 2 meters from the reactor core, and is moreover variable, extending continuously up to a range of about 10 meters. This proximity and variety combine to provide extraordinary sensitivity to a wide spectrum of oscillation scales, while facilitating the tidy cancellation of leading systematic uncertainties in the reactor source and environment. With 100~eV sensitivity, for exposures on the order of 200 kg$\cdot$y, we project an estimated sensitivity to first/fourth neutrino oscillation with a mass gap $\Delta m^2 \sim 1 \, {\rm eV}^2$ at an amplitude $\sin^2 2\theta \sim 10^{-1}$, or $\Delta m^2 \sim 0.2 \, {\rm eV}^2$ at unit amplitude. Larger exposures, around 5,000 kg$\cdot$y, together with 10 eV sensitivity are capable of probing more than an additional order of magnitude in amplitude.

Low-spin structure of Br513586 and Kr503686 nuclei: The role of the g7/2 neutron orbital

Low-spin excited levels in $_{35}^{86}\mathrm{Br}_{51}$ and $_{36}^{86}\mathrm{Kr}_{50}$, populated following ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay and the neutron-induced fission of $^{235}\mathrm{U}$, were measured using the Lohengrin fission-fragment separator and the EXILL array of Ge detectors at the PF1B cold-neutron facility of the Institute Laue-Langevin Grenoble. Improved populations of excited levels in $^{86}\mathrm{Br}$ remove inconsistencies existing in the literature on this nucleus. Directional-linear-polarization correlations, analyzed using newly developed formulas, as well as precise angular correlations allowed the unique ${1}^{\ensuremath{-}}$ and ${2}^{\ensuremath{-}}$ spin and parity assignments to the ground state of $^{86}\mathrm{Br}$ and the 4016.3-keV level in $^{86}\mathrm{Kr}$, respectively. Based on these results we propose that the Gamow-Teller ${\ensuremath{\beta}}^{\ensuremath{-}}$ decays of $^{86}\mathrm{Se}$ and $^{86}\mathrm{Br}$ involve the $\ensuremath{\nu}{g}_{7/2}\ensuremath{\rightarrow}\ensuremath{\pi}{g}_{9/2}$ transition in addition to the $\ensuremath{\nu}{p}_{3/2}\ensuremath{\rightarrow}\ensuremath{\pi}{p}_{3/2}$ transition proposed earlier. In $^{86}\mathrm{Kr}$ we have identified ${1}_{1}^{+}, {2}_{3}^{+}$, and ${3}_{1}^{+}$ levels, analogous to the mixed-symmetry states in $^{94}\mathrm{Mo}$, which in $^{86}\mathrm{Kr}$ are from proton excitations, only. Large-scale, shell-model calculations with refined interactions reproduce well excitations in $^{86}\mathrm{Br}$ and $^{86}\mathrm{Kr}$ and support our interpretations.

Structure of dipole bands in doubly odd Ag102

Excited states in the transitional doubly odd $^{102}\mathrm{Ag}$ nucleus were populated in the $^{75}\mathrm{As}(^{31}\mathrm{P},p3n)$ fusion-evaporation reaction using the 125 MeV incident $^{31}\mathrm{P}$ beam. The subsequent deexcitations were investigated through in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques using the Indian National Gamma Array spectrometer equipped with 21 clover Ge detectors. The level scheme in $^{102}\mathrm{Ag}$ has been established up to excitation energy $\ensuremath{\sim}6.5$ MeV and angular momentum $19\ensuremath{\hbar}$. The earlier reported level scheme is considerably extended and modified to result in a pair of nearly degenerate negative-parity dipole bands. Lifetime measurements for the states of these two dipole bands have been performed by using the Doppler-shift attenuation method. The two nearly degenerate bands exhibit different features with regard to kinetic moment of inertia, and the reduced transition probabilities $\mathrm{B}(M1)$ and $\mathrm{B}(E2)$, which do not favor these to be chiral partners. These bands are discussed in the framework of the hybrid version of tilted-axis cranking (tac) model calculations and assigned the $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}{({d}_{5/2}/{g}_{7/2})}^{2}$ configurations. The tac model calculations are extended to the nearly degenerate bands observed in the heavier doubly odd $^{104--108}\mathrm{Ag}$ isotopes.