Large-volume Germanium Detectors Research Articles

Measuring the Bremsstrahlung Yield upon the Alpha-Decay of 214Po

The results are presented from an experiment to measure the probability of internal bremsstrahlung upon the α-decay of the 214Po nucleus using a large-volume germanium detector and fast-time digitizers of signals from gamma and alpha detectors. Satisfactory agreement is obtained betw een the experimental data and the results from calculations in the literature, performed with the realistic and oscillatory nuclear potentials.

COMPASS—A COMPAct decay spectroscopy set-up

A compact silicon detector array with high spatial granularity and fast, fully digital data recording has been developed and commissioned for the investigation of heavy and superheavy nuclear species. The detector array can be combined in close geometry with large volume germanium detectors. It offers comprehensive particle and photon coincidence and correlation spectroscopy by highly efficient evaporation residue, α, γ, conversion electron and X-ray detection supported by the high granularity of the implantation chip. Access to fast decay events in the sub-microsecond region is made possible by the fast timing properties of the digital signal processing. A novel Si-chip support design allows direct cooling of the Si-chips and short signal transport. The compact and modular mechanical design equipped with a standard flange facilitates its transport and connection to different separators at different ion beam facilities. After initial tests, first α-γ coincidence spectroscopy experiments have been performed at the LISE separator of GANIL in Caen, France, in FULIS (velocity filter) mode and at the velocity filter SHIP of GSI in Darmstadt, Germany.

Using fast digital converters to detect bremsstrahlung radiation during the alpha decay of heavy nuclei

A large-volume germanium detector coupled with fast signal digitizers is proposed for use in experiments to study interference effects in yields of the bremsstrahlung radiation that accompanies alpha decays of heavy nuclei. When wavelet processing is applied to the signals from detectors, the time resolution can be as fine as ~30 ns for a detector with a volume of ≥100 cm3. This method is used to measure experimentally the probability of the emission of γ-quanta from excited states of daughter nuclei produced in the α-decay chain of 226Ra.

The Silicon Cube detector

A new experimental device, the Silicon Cube detector, consisting of six double-sided silicon strip detectors placed in a compact geometry was developed at CENBG. Having a very good angular coverage and high granularity, it allows simultaneous measurements of energy and angular distributions of charged particles emitted from unbound nuclear states. In addition, large-volume Germanium detectors can be placed close to the collection point of the radioactive species to be studied. The setup is ideally suited for isotope separation on-line (ISOL)-type experiments to study multi-particle emitters and was tested during an experiment at the low-energy beam line of SPIRAL at GANIL.

Towards a high-precision measurement of the 3He(α,γ)7Be cross section at LUNA

The 3He(4He, γ)7Be reaction is the key process for the production of 7Be and 8B neutrinos in the Sun. We have designed a new experimental setup to study this reaction with high accuracy at low energies using two different experimental techniques. The first method consists in measuring the prompt capture gamma-ray transitions with an ultra-low background germanium detector heavily shielded and placed at close distance from a 3He windowless gas target. With another fully shielded large-volume germanium detector we will also measure the β-decay of the 7Be residual nuclei. The aim of the experiment is to reduce the error on the astrophysical factor S3,4 to 4%.

Application of Hypermet-PC in PGAA

Hypermet-PC has been developed in the mid-nineties at the Institute of Isotopes and Surface Chemistry based on a successful FORTRAN code from the seventies. With additional calibration routines and other helping features it has proved to be a very useful tool in quantitative analysis performed either with NAA or with PGAA. The sophisticated built-in peak-shape function allows the fitting of asymmetric peaks from large-volume germanium detectors over a very wide energy range needed for PGAA. The experience collected when evaluating several thousands gamma-spectra acquired for routine analysis and spectroscopic research, is summarized in the paper.

An automatic energy-calibration method for segmented germanium detectors

An automatic gain-matching method has been developed for the energy calibrations of the 32 segments of a large-volume germanium detector. The method calibrates the small-volume segments relative to the central contact, which collects the charge from the total germanium crystal volume and can be efficiently calibrated with known sources. The method presented here can employ photons of arbitrary energy. With the use of in-beam γ-rays for segment calibrations it presents an efficient way to perform continuous energy calibrations in experiments.

Polarization sensitivity of a segmented HPGe detector up to [formula omitted

Linear γ-ray polarization can be measured using segmented germanium detectors. The polarization sensitivity of the Compton scattering process leads to asymmetries in the signals of a segmented detector. We have measured the polarization sensitivity of a four-fold segmented large volume germanium detector up to photon energies of approximately 10 MeV for the first time. The detector and its performance are compared to smaller Compton polarimeters which have been analyzed in previous work. A possible application of the described Compton polarimeter will be parity assignments in photon scattering experiments.

Studies of weak capture-γ-ray resonances via coincidence techniques

A method for measuring weak capture-γ-ray resonances via γγ-coincidence counting techniques is described. The coincidence apparatus consisted of a large-volume germanium detector and an annular NaI(Tl) crystal. The setup was tested by measuring the weak E R=227 keV resonance in 26Mg(p,γ) 27Al. Absolute germanium and NaI(Tl) counting efficiencies for a range of γ-ray energies and for different detector–target geometries are presented. Studies of the γ-ray background in our spectra are described. Compared to previous work, our method improves the detection sensitivity for weak capture-γ-ray resonances by a factor of ≈100. The usefulness of the present technique for investigations of interest to nuclear astrophysics is discussed.

Thirty-two-fold segmented germanium detectors to identify γ-rays from intermediate-energy exotic beams

Thirty-two-fold segmented coaxial high-purity large-volume germanium detectors for use in intermediate-energy radioactive-ion-beam experiments have been developed and tested. This high degree of segmentation will allow a precise localization of the point of photon interaction in the detector, thus allowing accurate doppler reconstruction of the energy of a γ-ray emitted in flight. In this article we report on the design of these detectors and their operational characteristics.

Radioactivity of neutron-rich oxygen, fluorine, and neon isotopes

The γ radiation and neutrons emitted following the β decays of 24O, 25–27F, and 28−30Ne have been measured. The nuclides were produced in the quasifragmentation of a 2.8 GeV 36S beam, separated in-flight and identified through time-of-flight and energy-loss measurements. The ions were stopped in a silicon detector telescope, which was used to detect the β particles emitted in their subsequent radioactive decay. The coincident γ rays were measured using four large volume germanium detectors mounted close to the implantation point and the neutrons were detected using 42 3He proportional counters. The measured γ-ray energy spectra are compared with shell model calculations and, where available, the level energies deduced from multinucleon transfer reactions.Received 1 February 1999DOI:https://doi.org/10.1103/PhysRevC.60.024311©1999 American Physical Society

Energy and efficiency calibration of an array of six Euroball Cluster detectors used for beta-decay studies

The use of an array of six Euroball Cluster detectors, i.e. 42 large-volume germanium detectors, for beta-decay studies is described. The solid angle with respect to a source placed in the center of the array amounts to 65% of 4π sr. The total photo-peak efficiency for 1.33 MeV γ-rays is 10.2(5)%, without “adding back” the Compton-scattered events. For this γ-ray energy, the energy resolution of the entire setup is 2.8 keV. The performance of the array up to γ-ray energies of 8 MeV is discussed, and alternative ways of determining the photo-peak efficiency are presented.

Beta decay of 31Ar

A complete study of 31Ar beta decay has been made by high-resolution charged-particle and gamma-ray spectroscopy. Beta-delayed radiation was detected by an array of three charged-particle detectors and a large-volume germanium detector. Fifteen new energy levels were discovered in 31Cl. The beta-strength distribution, measured to 14.5 MeV, is compared with a shell-model calculation in the full sd space. The quenching of the Gamow-Teller strength and the isospin impurity of the IAS in 31Cl are discussed.

Temperature and vacuum measurements on the commercial assembly of a large-volume Ge detector

This work reports on tests which have been extensively made on the assembly of a “dummy” large-volume germanium detector with the aim of measuring temperature gradients along the crystal, as well as in different parts of the cryostat, during the steady cold, room temperature and annealing phases and in the transitions between them. Measurements of the vacuum level and trends of the residual gas composition in the cryostat in the different phases of operation are also reported.

High count rate particle spectroscopy with silicon surface-barrier detectors

The technique of producing trapezoidal signals by means of a modified version of the DL-RC filter, which proved to work successfully when applied to gamma spectroscopy with large volume germanium detectors [1], has been extended to particle spectroscopy. The trapezoidal pulses, synthesized for particle energy measurements, have a flat top of 70 ns and a total duration of 270 ns. A fast stretcher was designed in order to properly process these short signals. A description of the trapezoidal DL-RC shaper, as well as of the fast linear gate and stretcher is given.The performance (linearity, energy resolution, throughput rate) of the overall system is reported.

Gamma spectroscopy at high counting rates with large volume germanium detectors

The energy resolution and the throughput rate of a quasi-trapezoidal filter, based on a modified version of the DL-RC circuit, have been studied as a function of the counting rate up to ∼10 5 counts per second. The performance of the modified DL-RC circuit is compared with that of a semi-Gaussian active filter and that of a quasi-trapezoidal gated integrator.

Spectroscopy of gamma rays fromAs78decay

Gamma rays accompanying the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{78}\mathrm{As}$ to $^{78}\mathrm{Se}$ have been studied using a high purity source and large volume germanium detectors. Seventeen new $\ensuremath{\gamma}$ rays have been observed and eight previously reported gamma rays have been excluded. From singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data new levels are proposed at 1758.9, 2334.9, 2647.7, and 3372.7 keV, whereas the 1693-, 1721-, 2452-, 2798-, 3192-, 3528-, and 3984-keV levels proposed in earlier studies have been withdrawn from the $^{78}\mathrm{As}$ decay scheme. Deduced $B(E2)$ ratios have been compared with theoretical calculations based on an anharmonic oscillator model.RADIOACTIVITY $^{78}\mathrm{As}$ [from $^{78}\mathrm{Se}$ ($n$,$p$)]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin; deduced: $^{78}\mathrm{Se}$ levels, $B(E2)$ ratios. Enriched $^{78}\mathrm{Se}$ target, Ge and Ge(Li) detectors.