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Abstract: The observation of anomalous charge collection in a P-type Point Contact (PPC) High Purity Germanium (HPGe) detector is reported. By studying preamplifier charge signals from the detector, these anomalous events are shown to be consistent with charge carrier drift along the surface of the detector, prior to collection at the contact. It is believed that these events arise from the formation of a surface channel in the detector. By coupling analysis of these experimental signals with field calculations, an estimate of the radial drift velocity of holes at the surface has been made. This value is found to be around 40 times slower than the accepted value for saturated hole drift in the bulk, and is in good agreement with that calculated using a newly developed technique for modelling carrier transport. [Copyright &y& Elsevier]

Abstract: A novel, large-volume High Purity Germanium (HPGe) detector that will provide gamma-ray detection with both sub-mm position resolution and high efficiency is under development. This design is based on a coaxial HPGe geometry and employs a point contact along with segmentation of the outer electrode. Calculations indicate that this device will be capable of achieving values of position sensitivity which are approximately a factor of four or five greater than conventional gamma-ray tracking detectors. [Copyright &y& Elsevier]

Abstract: In order to achieve background count rates sufficiently low so as to allow the observation of rare events such as neutrinoless double beta (0νββ) decay, background suppression techniques are routinely employed. In this paper we present details of a novel Pulse Shape Analysis algorithm, which allows single-site events such as 0νββ decay to be distinguished from multi-site background events in germanium detectors. The algorithm, which is based on the event-by-event χ 2 fitting of experimental signals to a basis data set of unique single-site pulse shapes, has been developed through simulation studies and tested experimentally using a Broad Energy Germanium detector. It is found experimentally that the technique is able to successfully identify and reject 99% of multi-site events in the single escape peak associated with the gamma decay of 208Tl, whilst maintaining a survival probability of 98% for neutrinoless double-beta-decay-like double escape peak events. [ABSTRACT FROM AUTHOR]

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the 132Sn region, including Coulomb excitation, fusion-evaporation, and neutron transfer. The value for first 2+ excited states of even-even neutron-rich 132–136Te and 126–134Sn have been measured by Coulomb excitation in inverse kinematics. The results are discussed in terms of the shell model and the quasiparticle random phase approximation. Neutron transfer onto a 134Te beam, from 9Be and 13C targets to populate single-particle states in 135Te, has also been studied. Gamma rays from the 13C(134Te, 12C) reaction were used to identify the state in 135Te, at an energy of 2109 keV. These and other results, and plans for future experiments with these neutron-rich beams, are presented. [Copyright &y& Elsevier]

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of exciting measurements around the 132Sn region, including Coulomb excitation, fusion-evaporation, and neutron transfer. The value for first 2+ excited states of neutron-rich 132,134,136Te and 126,128,130,132,134Sn have been measured by Coulomb excitation in inverse kinematics. The results are discussed in terms of the shell model and the quasiparticle random phase approximation. Neutron transfer onto a 134Te beam, from 9Be and 13C targets to populate single-particle states in 135Te, has also been studied. Results, and plans for future experiments with these neutron-rich beams, are presented. [Copyright &y& Elsevier]

Abstract High Purity germanium point-contact detectors have low energy thresholds and excellent energy resolution over a wide energy range, and are thus widely used in nuclear and particle physics. In rare event searches, such as neutrinoless double beta decay, the point-contact geometry is of particular importance since it allows for pulse-shape discrimination, and therefore for a significant background reduction. In this paper we investigate the pulse-shape discrimination performance of ultra-high purity germanium point contact detectors. It is demonstrated that a minimal net impurity concentration is required to meet the pulse-shape performance requirements. [ABSTRACT FROM AUTHOR]

Abstract: An approximate method for signal decomposition in -ray tracking detectors is presented, based on Singular Value Decomposition (SVD). With this algorithm, the CPU time scales linearly with the number of possible interaction sites for any number of interactions per ray. The method is also robust to uncertainty in the signal start time and is applicable to any -ray detectors with highly segmented crystals as well as any inverse problem that can be reduced to a search among a countable set of precalculated forward solutions. [Copyright &y& Elsevier]

The SIGMA Germanium detector has the potential to revolutionise γ -ray spectroscopy, providing superior energy and position resolving capabilities compared with current large volume state-of-the-art Germanium detectors. The theoretical position resolution of the detector as a function of γ -ray interaction position has been studied using simulated detector signals. A study of the effects of RMS noise at various energies has been presented with the position resolution ranging from 0.33 mm FWHM at E γ = 1 MeV , to 0.41 mm at E γ = 150 keV. An additional investigation into the effects pulse alignment have on pulse shape analysis and in turn, position resolution has been performed. The theoretical performance of SIGMA operating in an experimental setting is presented for use as a standalone detector and as part of an ancillary system. [ABSTRACT FROM AUTHOR]

We have characterized, for the first time, an n-type segmented inverted coaxial point-contact detector. This novel detector technology relies on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ -ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in this detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 ± 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values. [ABSTRACT FROM AUTHOR]

A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich 110 Ru ( t 1 / 2 = 12 s ) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations. [ABSTRACT FROM AUTHOR]

The sensitivity of the position resolution of the gamma-ray tracking array GRETINA to the hole charge-carrier mobility parameter is investigated. The χ 2 results from a fit of averaged signal (“superpulse”) data exhibit a shallow minimum for hole mobilities 15% lower than the currently adopted values. Calibration data on position resolution is analyzed, together with simulations that isolate the hole mobility dependence of signal decomposition from other effects such as electronics cross-talk. The results effectively exclude hole mobility as a dominant parameter for improving the position resolution for reconstruction of gamma-ray interaction points in GRETINA. [ABSTRACT FROM AUTHOR]

Abstract: The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is a new generation high-resolution spectrometer consisting of electrically segmented high-purity germanium crystals. GRETINA is capable of reconstructing the energy and position of each interaction point inside the crystal with high resolution. This enables energy tracking which in turn provides an array with large photopeak efficiency, high resolution and good peak-to-total ratio. GRETINA is used for nuclear structure studies with demanding detection requirements and it is suitable for experiments with radioactive-ion beams with high recoil velocities. The GRETINA array has a solid angle coverage and constitutes the first stage towards the full array GRETA. We present in this paper the main parts and the performance of the GRETINA system. [Copyright &y& Elsevier]

Abstract: In the crystal bulk of group IV covalent semiconductors such as germanium (Ge), simple analytic models for the valence band structure can provide fast, accurate computations of hole mobility for moderate energy ranges up to a few eV. On the surfaces of these materials, such as on Ge-vacuum or Ge–GeO2 interfaces, the transport rates differ significantly from the bulk. This can be problematic for both point contact and segmented Ge gamma ray detectors, that require accurate carrier drift rates for computing signal basis sets, which themselves are necessary for the precise determination of gamma-ray induced compton scattering events. While several techniques exist for computing surface hole mobilities, more often than not, these methods are complex to implement, require significant computational resources, and lack the simplicity of bulk models for interpreting results. This paper presents a new technique for computing Ge surface hole mobility that can give a first estimate for the surface transport rates after tuning a physically based computational parameter. This model is used in conjunction with particle-in-cell (PIC) simulations for modeling hole-dynamics inside a Ge p-type point contact detector. The results of our calculations agree with experimental data gathered from Ge p-type point contact detectors at Oak Ridge National Laboratory. [Copyright &y& Elsevier]

Abstract: The g factor of the state in 132 52Te, , , was measured by the transient field technique applied to a radioactive beam. The development of an experimental approach necessary for work in radioactive beam environments is described. The result agrees with the previous measurement by the recoil-in-vacuum technique, but here the sign of the g factor is measured as well. [Copyright &y& Elsevier]

Abstract: We demonstrate that the recoil-in-vacuum (RIV) method can be used to determine the g-factor of the Coulumb excited first 2+ state of 132Te. This was possible owing to advantages provided by CLARION (ORNL clover multi-detector array) and the segmented charged particle detector HyBall. Calibratory experiments were performed with 122,126,130Te and a g-factor of 132Te was deduced g =(+)0.35(5). [Copyright &y& Elsevier]

Abstract: The position resolution of a highly segmented coaxial germanium detector was determined by analyzing the 2055keV -ray transition of excited in a fusion–evaporation reaction. The high velocity of the nuclei imparted large Doppler shifts. Digital analysis of the detector signals recovered the energy and position of individual -ray interactions. The location of the first interaction in the crystal was used to correct the Doppler energy shift. Comparison of the measured energy resolution with simulations implied a position resolution (root mean square) of 2mm in three-dimensions. [Copyright &y& Elsevier]

We have measured the B(E;0+ → 2+) for the first excited 2+ states in the double-closed shell nucleus 132Sn and the two-neutron nucleus 134Sn. The results, based on a preliminary analysis are shown in Fig. 1 along with measurements on the stable Sn isotopes, and earlier results on 126,128,130Sn . The experimental setup developed for the 132,134Sn measurements was also employed in a successful measurement of B(E;0+ → 2+) for the closed-neutron-shell nucleus 82Ge. [Copyright &y& Elsevier]

Evaporation residue cross sections have been measured with neutron-rich radioactive 132Sn beams on 64Ni in the vicinity of the Coulomb barrier. The average beam intensity was 2 × 104 particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. The measurement is compared to coupled-channel calculations taking into account inelastic excitation and nucleon transfer. [Copyright &y& Elsevier]

A method whereby mass differences can be measured using the 25-MV tandem accelerator at the Holifield radioactive ion beam facility (HRIBF) is presented. The technique is unconventional in that mass differences will be measured as position differences at the image of the energy-analyzing magnet following the accelerator and will be made at energies where independent isobaric determination will be possible by a ΔE measurement. The technique is appropriate where the unknown mass is the most neutron-rich isobaric constituent of the beam, such as for neutron-rich fission fragments. [Copyright &y& Elsevier]

A novel background subtraction method for Doppler-shift attenuation and angular correlation measurements with large multi-detector HpGe arrays is presented. The formalism is designed for recently developed data base storage techniques with the event format resembling the original raw data structure. The background spectrum is constructed based on parameters extracted from one-dimensional spectra; the method, therefore, is complementary to currently applied methods which are designed for multi-dimensional, symmetrized histograms. [Copyright &y& Elsevier]

The SIGMA project aims to develop a p-type segmented inverted coaxial point contact germanium detector for gamma-ray tracking and imaging. The performance of the first prototype of this type of detector is reported. The measurements performed verified the size and shape of the crystal and determined the location of the complex active volumes of the detector segments. The latter determines the charge collection times that are related to the position of interaction. Good agreement is found between the results and the specified crystal design. The energy resolution of the point contact has been measured to be 0.84 keV and 2.21 keV at 122 keV and 1332 keV, respectively. [ABSTRACT FROM AUTHOR]