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Abstract: Methods to optimize the performance of the TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS), an array of 12 large-volume, 32-fold segmented HPGe clover detectors to be used at the ISAC-II radioactive ion beam facility, have been developed based on GEANT4 Monte Carlo simulations. These methods rely on the segmentation of the outer electrical contacts of the TIGRESS HPGe clovers, and on the 20-fold segmentation of the Compton-suppression shields. The clover segmentation is utilized to make event-by-event decisions as to whether the -ray energy depositions in neighbouring crystals and clovers will be summed. The Compton suppressor segmentation is used to veto events selectively, and to reduce false suppression in experiments with high -ray multiplicity. Procedures to determine the optimal techniques and configurations of the array for a particular experiment, dependent on the expected -ray energies and multiplicities, and the velocity of the recoil ions, are presented. [Copyright &y& Elsevier]

High-resolution γ-ray spectroscopy is one of the most powerful and versatile experimental techniques in low-energy nuclear physics research. With the continuing development of hyper-pure germanium (HPGe) detector technology, including multi-crystal detectors, contact segmentation, and digital signal processing techniques, large γ-ray detector arrays will continue to play a major role in the experimental programs at existing and future radioactive ion beam facilities. This paper provides an overview of recent progress in, and future plans for, the development of large γ-ray spectrometers at such facilities, including the recent commissioning of the 8π spectrometer at ISAC-I and the proposed TRIUMF-ISAC gamma-ray escape suppressed spectrometer array for the ISAC-II facility. [Copyright &y& Elsevier]

Abstract: The wave-function composition for the low-lying states in 29Na was explored by measuring their electromagnetic properties using the Coulomb-excitation technique. A beam of 29Na ions, postaccelerated to 70 MeV, bombarded a 110Pd target with a rate of up to 600 particles per second at the recently commissioned ISAC-II facility at TRIUMF. Six segmented HPGe clover detectors of the TIGRESS γ-ray spectrometer were used to detect deexcitation γ rays in coincidence with scattered or recoiling charged particles in the segmented silicon detector, BAMBINO. The reduced transition matrix element in 29Na was derived to be 0.237(21) e b from the measured γ-ray yields for both projectile and target. This first-time measured value is consistent with the most recent Monte Carlo shell-model calculation, indicating a significant admixture of both sd and pf components in the wave function, and also providing evidence for the narrowing of the neutron shell gap from for stable nuclei to for 29Na. [Copyright &y& Elsevier]

Abstract: The diffusion-limited release of radioactive 120Xe from several thin metal foils abruptly heated to temperatures of order 1000°C while in a vacuum is characterized and interpreted in terms of impurity atom diffusion coefficients. The 120Xe impurities were produced in situ from the decay of 120Cs implanted into Ta, Pt, and Zr foils from a 30keV mass-separated ion beam. The temperature dependence of the diffusion coefficients extracted from our data is well described by Arrhenius relations, for which best-fit parameters are presented. The fastest release of 120Xe for a given set of implantation conditions and temperature is observed for Zr, although its reactivity may prove problematic for its use as a catcher foil. A number of convenient analytic formulae for the diffusion-limited release of impurity atoms are presented. [Copyright &y& Elsevier]