Germanium Array Research Articles

Hypernuclear physics studies of the P̅ANDA experiment at FAIR

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). [1, 2] Thanks to the use of stored p beams, copious production of double Λ hypernuclei is expected at the PANDA experiment, which will enable high precision γ spectroscopy of such nuclei for the first time, and consequently a unique chance to explore the hyperon-hyperon interaction. In particular, ambiguities of past experiments in determining the strength of the ΛΛ interaction will be avoided thanks to the excellent energy precision of a few keV (FWHM) achieved by germanium detectors. Such a resolution capability is particularly needed to resolve the small energy spacing of the order of (10–100) keV, which is characteristic from the spin doublet in hypernuclei the so –called “hypernuclear fine structure”.In comparison to previous experiments, PANDA will benefit from a novel technique to assign the various observable γ -transitions in a unique way to specific double hypernuclei by exploring various light targets. Nevertheless, the ability to carry out unique assignments requires a devoted hypernuclear detector setup. This consists of a primary nuclear target for the production of Ξ− + pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform γ spectroscopy.Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. Accordingly, the need of an innovative detector concept will require dramatic improvements to fulfil these conditions and that will likely lead to a new generation of detectors. In the present work details concerning the current status of the activities related to the detector developments for this challenging programme will be given.Among these improvements is the new concept for a cooling system for the germanium detector based on a electro-mechanical device. In the present work, the cooling efficiency of such devices has been successfully tested, showing their capability to reach liquid nitrogen temperatures and therefore the possibility to use them as a good alternative to the standard liquid nitrogen dewars. Furthermore, since the momentum resolution of low momentum particles is crucial for the unique identification of hypernuclei, an analysis procedure for improving the momentum resolution in few layer silicon based trackers is presented.

Spectroscopy ofGd153andGd157using the(p,dγ)reaction

Low-spin single quasineutron levels in $^{153}\mathrm{Gd}$ and $^{157}\mathrm{Gd}$ have been studied following the $^{154}\mathrm{Gd}$($p,d\ensuremath{-}\ensuremath{\gamma}$)$^{153}\mathrm{Gd}$ and $^{158}\mathrm{Gd}$($p,d\ensuremath{-}\ensuremath{\gamma}$)$^{157}\mathrm{Gd}$ reactions. A combined Si telescope and high-purity germanium array was utilized, allowing $d\text{\ensuremath{-}}\ensuremath{\gamma}$ and $d\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements. Almost all of the established low-excitation-energy, low-spin structures were confirmed in both $^{153}\mathrm{Gd}$ and $^{157}\mathrm{Gd}$. Several new levels and numerous new $\ensuremath{\gamma}$ rays are observed in both nuclei, particularly for ${E}_{x}\ensuremath{\ge}1$ MeV. Residual effects of a neutron subshell closure at $N=64$ are observed in the form of a large excitation energy gap in the single quasineutron level schemes.

Hypernuclear physics studies of the PANDA experiment at FAIR

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). http://www. gsi.de, http://www.gsi.de/fair/ Thanks to the use of stored \(\overline {p}\) beams, copious production of double Λ hypernuclei is expected at the PANDA experiment, which will enable high precision γ spectroscopy of such nuclei for the first time, and consequently a unique chance to explore the hyperon-hyperon interaction. In particular, ambiguities of past experiments in determining the strength of the ΛΛ interaction will be avoided thanks to the excellent energy precision of a few keV (FWHM) achieved by germanium detectors. Such a resolution capability is particularly needed to resolve the small energy spacing of the order of (10–100) keV, which is characteristic from the spin doublet in hypernuclei the so -called ”hypernuclear fine structure”. In comparison to previous experiments, PANDA will benefit from a novel technique to assign the various observable γ-transitions in a unique way to specific double hypernuclei by exploring various light targets. Nevertheless, the ability to carry out unique assignments requires a devoted hypernuclear detector setup. This consists of a primary nuclear target for the production of \({\Xi }^{-}+\overline {\Xi }\) pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform γ spectroscopy. Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. Accordingly, the need of an innovative detector concept will require dramatic improvements to fulfil these conditions and that will likely lead to a new generation of detectors. In the present talk details concerning the current status of the activities related to the detector developments for this challenging programme will be given. Among these improvements is the new concept for a cooling system for the germanium detector based on a electro-mechanical device. In the present work, the cooling efficiency of such devices has been successfully tested, showing their capability to reach liquid nitrogen temperatures and therefore the possibility to use them as a good alternative to the standard liquid nitrogen dewars. Furthermore, since the momentum resolution of low momentum particles is crucial for the unique identification of hypernuclei, an analysis procedure for improving the momentum resolution in few layer silicon based trackers is presented.

Experimental study of bound states in12Be through low-energy11Be(d,p)-transfer reactions

The bound states of 12Be have been studied through a 11Be(d,p)12Be transfer reaction experiment in inverse kinematics. A 2.8 MeV/u beam of 11Be was produced using the REX-ISOLDE facility at CERN. The outgoing protons were detected with the T-REX silicon detector array. The MINIBALL germanium array was used to detect gamma rays from the excited states in 12Be. The gamma-ray detection enabled a clear identification of the four known bound states in 12Be, and each of the states has been studied individually. Differential cross sections over a large angular range have been extracted. Spectroscopic factors for each of the states have been determined from DWBA calculations and have been compared to previous experimental and theoretical results.

Study of collisions of 136Xe + 198Pt for the KEK isotope separator

Multinucleon transfer reactions between two heavy ions are an important tool for production and investigation of exotic neutron-rich nuclei, which are difficult to access by other methods. The 136Xe+198Pt system is a candidate to efficiently produce neutron-rich nuclei around the neutron magic number N=126 for the KEK isotope separation project. In order to confirm this, measurements of the production cross sections with the large acceptance magnetic spectrometer VAMOS++ and de-excitation gamma rays from target-like fragments using the high efficiency germanium array EXOGAM at GANIL are reported. The measured isotopic distributions of the projectile-like fragments are compared with GRAZING calculations. The proton stripping channels show rough agreements between measurements and calculations. For the proton pick-up channels, the measured distributions are shifted toward the heavier masses and show enhanced cross sections in transfers of two or more protons.

High precision γ spectroscopy of ΛΛ-Hypernuclei at the PANDA experiment

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at FAIR at Darmstadt (Germany). Thanks to the use of stored antiproton beams, copious production of double ΛΛ-Hypernuclei is expected at the PANDA experiment, which will enable high precision gamma spectroscopy of such nuclei for the first time. At PANDA excited states of hypernuclei will be used as a starting point for the formation of double ΛΛ-Hypernuclei. In order to predict the yield of particle-stable double hypernuclei a microcanonical decay model was developed. For the detection of these nuclei, a devoted hypernuclear detector setup is planned. This set-up consists, in addition to the general purpose of the PANDA set-up, of a primary nuclear target for the production of pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform gamma spectroscopy. Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. In these proceedings details concerning the identification procedure of double hypernuclei and the suppression of background will be presented. In addition, the current status of the activities related to the detector developments for this challenging programme will be briefly given.

Lifetime measurements on fission fragments in the A ∼ 100 region

Lifetimes of first 4+ and 6+ states have been measured in neutron-rich isotopes of Zr, Mo, Ru and Pd using the recoil distance Doppler shift method at GANIL. The nuclei were produced through a fusion-fission reaction in inverse kinematics. The fission fragments were fully identified in the large-acceptance VAMOS spectrometer and γ -rays were detected in coincidence with the EXOGAM germanium array. Lifetimes of excited states in the range of 1–100 ps were measured with the Cologne plunger. Preliminary lifetime results are presented as well as a discussion on the evolution of the collectivity in this region.

Neutron-inducedγ-ray production cross sections for the first excited-state transitions in20Ne and22Ne

Background: Neutron-induced reactions are a significant concern for experiments that require extremely low levels of radioactive backgrounds. Measurements of $\ensuremath{\gamma}$-ray production cross sections over a wide energy range help to predict and identify neutron backgrounds in these experiments.Purpose: The purpose of this experiment is to determine partial $\ensuremath{\gamma}$-ray production cross sections for neutron-induced reactions in natural neon.Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used for the measurement. Gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE).Results: Partial $\ensuremath{\gamma}$-ray cross sections were measured for the first excited-state transitions in ${}^{20}$Ne and ${}^{22}$Ne. The measured cross sections were compared to the talys and CoH${}_{3}$ nuclear reaction codes.Conclusions: These are the first experimental data for ($n,{n}^{\ensuremath{'}}$) reactions in neon. In addition to providing data to aid in the prediction and identification of neutron backgrounds in low-background experiments, these new measurements will help refine cross-section predictions in a mass region where models are not well constrained.

Empirical correction of crosstalk in a low-background germanium γ–γ analysis system

The Pacific Northwest National Laboratory (PNNL) is currently developing a custom software suite capable of automating many of the tasks required to accurately analyze coincident signals within gamma spectrometer arrays. During the course of this work, significant crosstalk was identified in the energy determination for spectra collected with a new low-background intrinsic germanium (HPGe) array at PNNL. The HPGe array is designed for high detection efficiency, ultra-low-background performance, and sensitive γ–γ coincidence detection. The first half of the array, a single cryostat containing seven HPGe crystals, was recently installed into a new shallow underground laboratory facility. This update will present a brief review of the germanium array, describe the observed crosstalk, and present a straight-forward empirical correction that significantly reduces the impact of this crosstalk on the spectroscopic performance of the system.

β-delayed proton emission in the100Sn region

Beta-delayed proton emission from nuclides in the neighborhood of 100Sn was studied at the National Superconducting Cyclotron Laboratory. The nuclei were produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be target. Beam purification was provided by the A1900 Fragment Separator and the Radio Frequency Fragment Separator. The fragments of interest were identified and their decay was studied with the NSCL Beta Counting System (BCS) in conjunction with the Segmented Germanium Array (SeGA). The nuclei 96Cd, 98Ing, 98Inm and 99In were identified as beta-delayed proton emitters, with branching ratios bp = 5.5(40)%, 5.5+3 -2%, 19(2)% and 0.9(4)%, respectively. The bp for 89Ru, 91,92Rh, 93Pd and 95Ag were deduced for the first time with bp = 3+1.9 -1.7%, 1.3(5)%, 1.9(1)%, 7.5(5)% and 2.5(3)%, respectively. The bp = 22(1)% for 101Sn was deduced with higher precision than previously reported. The impact of the newly measured bp values on the composition of the type-I X-ray burst ashes was studied.

Partialγ-ray production cross sections for (n,xnγ) reactions in natural argon at 1–30 MeV

Background: Neutron-induced backgrounds are a significant concern for experiments that require extremely low levels of radioactive backgrounds such as direct dark matter searches and neutrinoless double-beta decay experiments. Unmeasured neutron scattering cross sections are often accounted for incorrectly in Monte Carlo simulations. Purpose: Determine partial gamma-ray production cross sections for (n,xng) reactions in natural argon for incident neutron energies between 1 and 30 MeV. Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used used for the measurement. Neutron energies were determined using time-of-flight and resulting gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE). Results: Partial gamma-ray cross sections were measured for six excited states in Ar-40 and two excited states in Ar-39. Measured (n,xng) cross sections were compared to the TALYS and CoH3 nuclear reaction codes. Conclusions: These new measurements will help to identify potential backgrounds in neutrinoless double-beta decay and dark matter experiments that use argon as a detection medium or shielding. The measurements will also aid in the identification of neutron interactions in these experiments through the detection of gamma rays produced by (n,xng) reactions.

Near-yrast structure of odd-A, neutron-rich Pr isotopes

The neutron-rich praseodymium isotopes ${}^{151}$Pr and ${}^{153}$Pr have been studied by prompt $\ensuremath{\gamma}$-ray spectroscopy using ${}^{248}$Cm and ${}^{252}$Cf spontaneous-fission sources placed inside the EUROGAM-II and Gammasphere germanium arrays, respectively. Rotational bands based on $3/{2}^{\ensuremath{-}}$[541] states, with similar structures, have been assigned to these nuclei. These bands decay by intraband $E2$ transitions. Interband $E1$ transitions, reported in other works, were not observed. Delayed conversion-electron and $\ensuremath{\gamma}$-ray spectroscopy of an $A=151$ nucleus has been performed at the Lohengrin mass spectrometer. A previously reported 35.1-keV isomer of ${}^{151}$Pr has been determined to decay by an $E1$ transition, and its half-life of 50(8) $\ensuremath{\mu}$s has been measured. Calculations performed using a reflection-symmetric quasi-particle-rotor model successfully reproduce the energies of the excited states of these nuclei and their decay patterns. The spin of the isomer has been assigned to be (1/2${}^{+}$, 3/2${}^{+}$) from a comparison with the calculations. The long half-life of this isomer and the lack of intraband $E1$ transitions show an absence of strong octupole correlations in the observed states of ${}^{151,153}$Pr. This is explained in terms of increasing quadrupole deformation reducing the number of Nilsson orbitals close to the Fermi surface available to form octupole collectivity.

A new low-energy radioactive beam line for nuclear astrophysics studies in China

A gas-target system has been newly developed and installed at a Radioactive Ion Beam Line in Lanzhou (RIBLL), which makes RIBLL capable of delivering intense, low-energy RIBs for nuclear astrophysics studies. A 1.7×104-pps intensity 22Na RI beam has been achieved in a commissioning run. With further improvements, a 105-pps intensity of some RI beams with mass A<30 (close to the line of β-stability) can be expected in the near future. Some detection equipment including Germanium and Silicon arrays (or balls) available (or to be constructed) at IMP are briefly introduced. A new low-energy radioactive beam line in China is now ready for nuclear astrophysics studies.

From RISING to the DESPEC fast-timing project within NUSTAR at FAIR: Sub-nanosecond nuclear timing spectroscopy with LaBr3 scintillators

This paper summarises a presentation given at the IRRMA8 conference in June 2011 which reviewed briefly the topic of current research studies in the evolution of nuclear structure with changing proton and neutron numbers. A short review of relevant contemporary spectroscopic studies of the structure of nuclei with highly exotic N/Z ratios using projectile fragmentation and fission reactions is given, together with an overview of some of the physics research aims to be attacked using the proposed Decay Spectroscopy (DESPEC) LaBr3 Fast-Timing gamma-ray array for the NUSTAR project at the upcoming Facility for Anti-Proton and Ion Research (FAIR). Examples of recent results using both ‘isomer’ and β−-delayed gamma-ray decay measurements with the Stopped RISING hyper-pure germanium array at GSI are summarised and used to highlight some of the fundamental physics studies which are expected to become available in this area of research in the coming decade. Examples of the performance of cerium-doped LaBr3 detectors from ‘in-beam’ test experiments are presented together with initial plans for the geometry of the planned multi-detector LaBr3(Ce) array for DESPEC.

Double Λ-hypernuclei at the PANDA experiment

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). Thanks to the use of stored \(\overline{p}\) beams, copious production of double Λ hypernuclei is expected at the PANDA experiment, which will enable high precision γ spectroscopy of such nuclei for the first time. At PANDA excited states of Ξ − hypernuclei will be used as a starting point for the formation of double Λ hypernuclei. In order to predict the yield of particle stable double hypernuclei a microcanonical decay model was developed. For the detection of these nuclei, a devoted hypernuclear detector setup is planned. This set-up consists, in addition to the general purpose of the PANDA set-up, of a primary nuclear target for the production of \(\Xi^{-}+\overline{\Xi}\) pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform γ spectroscopy. Furthermore, the presence of \(\overline{\Xi}\) can be used as an alternative to tag the strangeness in the \(\Xi^{-}+\overline{\Xi}\). All systems need to operate in the presence of a high magnetic field and a large hadronic background. In the present talk details concerning simulations, the identification procedure of double hypernuclei and the suppression of background will be presented. In addition, the present status of the detector developments for this programme will be briefly given.

The gamma efficiency of the GAINS spectrometer

The GAINS (Germanium Array for Inelastic Neutron Scattering) setup was recently installed at the GELINA (Geel Linear Accelerator) neutron source of EC-JRC-IRMM. In order to produce reliable neutron inelastic cross-section data the setup requires a precise efficiency calibration for each sample under investigation. These samples represent extended sources in non-standard orientations and with significant self-attenuation of gamma rays. We present in detail the efficiency calibration procedure performed with two Monte Carlo simulations using MCNP and GEANT4. A good agreement is found between the two independent approaches. The general features of the simulations are discussed together with an in-depth description of the various factors influencing the efficiency.

Indian National Gamma Array at Inter University Accelerator Centre, New Delhi

A 4π multi-detector gamma-ray spectrometer named the Indian National Gamma Array (INGA) has been set up at the Inter University Accelerator Centre, New Delhi, for nuclear structure studies. The array is designed to incorporate twenty four Compton-suppressed Clover germanium detectors with a total photopeak efficiency ∼5%. The spectrometer along with sub-systems developed in-house like, mechanical support structure, high voltage power supplies, automatic liquid nitrogen filling system, front-end electronics and data acquisition system are described. The mechanical support structure facilitates the use of the Clover Germanium array with a recoil mass separator. The array has been used in a number of nuclear spectroscopic investigations. The in-beam and off-beam performance of the array are reported.

Isomeric states in neutron-deficientA~80–90nuclei populated in the fragmentation ofAg107

The relativistic projectile fragmentation of a 750 MeV per nucleon beam of Ag-107 was used to populate isomeric states in neutron-deficient nuclei around A=80-90. Reaction products were separated and unambiguously identified using the GSI FRagment Separator (FRS) and its ancillary detectors. At the final focal plane, the fragments were slowed from relativistic energies by means of an aluminium degrader and implanted in a passive stopper in the center of the high-efficiency, high-granularity Stopped Rare Isotope Spectroscopic INvestigation at GSI (RISING) germanium array. This allowed the identification of excited states in the N=Z nuclei Tc-86(43) and, for the first time, Nb-82(41). Isomeric states have also been identified for the first time in Tc-87,Tc-88, and a previously unreported isomer was observed in Nb-84. Experimental results are presented along with a discussion on the structure of these nuclei based on interpretations provided by several theoretical models. (Less)

( n,2 n) and ( n,3 n) cross-sections of neutron-induced reactions on 150Sm for [formula omitted] MeV

Cross-section measurements were made of prompt discrete γ -ray production as a function of incident neutron energy ( E n = 1 – 135 MeV ) on a 150Sm sample of 1550 mg / cm 2 of Sm 2 O 3 enriched to 95.6% in 150Sm. Results are compared with enhanced Hauser–Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ -rays were detected with the compton-suppressed germanium array for neutron-induced excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ -rays up to E x = 0.8 MeV in 149Sm and one γ -ray transition between the first excited and ground state in 148Sm were measured. Partial γ -ray cross-sections were calculated using GNASH, an enhanced Hauser–Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic “global” optical model potential parameters. A coupled-channels optical model based on a soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin-distribution in 150Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. The partial cross-sections for discrete γ -ray cascade paths leading to the ground state in 149Sm and 148Sm have been summed (without double counting) to estimate lower limits for reaction cross-sections. These lower limits are combined with Hauser–Feshbach model calculations to deduce the reaction channel cross-sections. These reaction channel cross-sections agree with previously measured experimental and ENDF/B-VII evaluations.

Digital Data Acquisition System for experiments with segmented detectors at National Superconducting Cyclotron Laboratory

A 624-channel Digital Data Acquisition System capable of instrumenting the Segmented Germanium Array at National Superconducting Cyclotron Laboratory has been implemented using Pixie-16 Digital Gamma Finder modules by XIA LLC. The system opens an opportunity for determination of the first interaction position of a γ ray in a SeGA detector from implementation of γ ‐ ray tracking. This will translate into a significantly improved determination of angle of emission, and in consequence much better Doppler corrections for experiments with fast beams. For stopped-beam experiments the system provides means for zero dead time measurements of rare decays, which occur on time scales of microseconds.