A. J. Boston

TIGRESS: TRIUMF-ISAC gamma-ray escape-suppressed spectrometer

The TRIUMF-ISAC gamma-ray escape-suppressed spectrometer (TIGRESS) is a new γ-ray detector array being developed for use at TRIUMFs Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. TIGRESS will comprise 12 32-fold segmented clover-type HPGe detectors coupled with 20-fold segmented modular Compton suppression shields and custom digital signal processing electronics. This paper provides an overview of the TIGRESS project and progress in its development to date.

The GRT4 VME pulse processing card for segmented germanium detectors

A four channel VME card with 14 bit, 80 MHz digitizers and powerful on-board processing has been designed, built and used in tests of digital pulse processing techniques for gamma-ray tracking. This paper explains the background (rationale for the project), describes the VME card (known as the GRT4) and presents a 64 channel GRT4 digitizing system which was used to instrument two segmented Germanium detectors during in-beam tests. Results obtained using the GRT4 card are presented as well as some applications.

First results on double β-decay modes of Cd, Te, and Zn Isotopes

T. Bloxham, A. Boston, J. Dawson, D. Dobos, S.P. Fox, M. Freer, B.R. Fulton, C. Gößling, P.F. Harrison, M. Junker, H. Kiel, J. McGrath, B. Morgan, D. Münstermann, P. Nolan, S. Oehl, Y. Ramachers, C. Reeve, D. Stewart, R. Wadsworth, J.R. Wilson, and K. Zuber School of Physics and Astronomy, University of Birmingham, B15 2TT, UK Lehrstuhl für Experimentelle Physik IV, Universität Dortmund, Otto–Hahn Str. 4,44227 Dortmund, Germany Laboratori Nazionali del Gran Sasso, S.S. 17 BIS km. 18.910, 67010, Assergi, L’Aquila, Italy Dept. of Physics, University of Liverpool, Liverpool L69 7ZE, UK Dept. of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK Dept. of Physics, University of Warwick, Coventry CV4 7AL, UK Dept. of Physics, University of York, Heslington, York, YO10 5DD, UK (Dated: February 5, 2008)

Production of antihydrogen at reduced magnetic field for anti-atom trapping

We have demonstrated production of antihydrogen in a 1 T solenoidal magnetic field. This field strength is significantly smaller than that used in the first generation experiments ATHENA (3 T) and ATRAP (5 T). The motivation for using a smaller magnetic field is to facilitate trapping of antihydrogen atoms in a neutral atom trap surrounding the production region. We report the results of measurements with the Antihydrogen Laser PHysics Apparatus (ALPHA) device, which can capture and cool antiprotons at 3 T, and then mix the antiprotons with positrons at 1 T. We infer antihydrogen production from the time structure of antiproton annihilations during mixing, using mixing with heated positrons as the null experiment, as demonstrated in ATHENA. Implications for antihydrogen trapping are discussed.

The Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND)

The observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neu-trinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 1028 years, using existing resources as appropriate to expedite physics results.

The TMR network project "Development of γ-ray tracking detectors"

The next generation of 4 pi arrays for high-precision gamma -ray spectroscopy will involve gamma -ray tracking detectors. They consist of high-fold segmented Ge detectors and a front-end electronics, based on new digital signal processing techniques, which allows to extract energy, timing and spatial information for a gamma -ray by pulse shape analysis of the Ge detector signals. Utilizing the information on the positions of the interaction points and the energies released at each point the tracks of the gamma -rays in a Ge shell can be reconstructed in three dimensions.

Validation of Pulse Shape Simulations for an AGATA Prototype Detector

An AGATA symmetric, coaxial, high-purity germanium (HPGe) detector has been scanned in coincidence mode. Charge pulse shapes from the 36-fold segmented outer contacts and center contact were stored for events at more than 2000 precisely determined 3-D interaction positions spread over ten depths (z). A database (basis) of the 37 average experimental pulse shapes at each position was generated. The electric field simulation code Multi Geometry Simulation (MGS) was used to generate the pulse shapes for the geometry on a 1.0-mm cubic grid. A minimization between the experimental pulse shapes at each position and the MGS basis yielded mean displacements of between 1.5 and 3.0 mm in the x- y plane. The vectors of these displacements were biased in the direction of the center of the detector. This effect is attributed to cross-talk. The maximum level of derivative cross-talk was measured and shown to be 534%ns. However due to the lack of a global clock in the acquisition system, it could not be accounted for throughout the basis.

Detailed spectroscopy of the normally deformed states in 132Ce

Abstract High-spin states have been studied in 132 Ce produced in the 100 Mo( 36 S,4nγ) reaction using the EUROGAM II spectrometer. The structure of the normally deformed states ( β 2 ∼ 0.2) has been investigated. Eight ΔI = 2 bands and three ΔI = 1 bands have been identified and the level scheme extended up to spin and parity (40 + ) at an excitation energy 19.79 MeV. The results are interpreted with the aid of Woods-Saxon cranking calculations, which suggest a variety of triaxial (γ) shapes in this nucleus stabilised by specific active quasiparticle orbitals.

Evidence for multiple band terminations in 102Pd

Abstract The level structure of 102 Pd has been investigated using data collected with the Eurogam 2 array. Several cascades of γ-rays have been established up to high spins. Termination of rotational bands has been observed at I π = 28 − and 32 + , and tentatively at I π = 38 + and 42 + . The nucleus 102 Pd is the first case where rotational bands built on valence space configurations are followed from spin close to zero up to termination and, at higher spins, a smooth rotational band which appears to terminate is built on core excited configurations.

Characterisation Results From an AGATA Prototype Detector

An Advanced GAmma Tracking Array (AGATA) symmetric prototype high purity Germanium (HPGe) detector has been tested. The detector was illuminated with a 1 mm collimated beam of 137Cs (662 keV) gamma rays. The beam was raster scanned across the front and sides of the detector and the charge sensitive preamplifier output pulse shapes from all 37 channels (36 segments plus the centre contact) were digitised and stored for off-line analysis. Rise time and image charge asymmetry magnitudes were measured as a function of interaction position to study the charge transport properties through the crystal volume. These parameters were then utilised as a calibrated look up table with which in-beam data was analysed and Doppler corrected. An average position resolution of approximately 9 mm (FWHM) was achieved with a crude analysis.