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Abstract: Methods of optimizing the performance of an array of Compton-suppressed, segmented HPGe clover detectors have been developed which rely on the physical position sensitivity of both the HPGe crystals and the Compton-suppression shields. These relatively simple analysis procedures promise to improve the precision of experiments with the TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). Suppression schemes will improve the efficiency and peak-to-total ratio of TIGRESS for high γ-ray multiplicity events by taking advantage of the 20-fold segmentation of the Compton-suppression shields, while the use of different summing schemes will improve results for a wide range of experimental conditions. The benefits of these methods are compared for many γ-ray energies and multiplicities using a GEANT4 simulation, and the optimal physical configuration of the TIGRESS array under each set of conditions is determined. [Copyright &y& Elsevier]

Abstract: Tests of the performance of a 32-fold segmented HPGe clover detector coupled to a 20-fold segmented Compton-suppression shield, which form a prototype element of the TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS), have been made. Peak-to-total ratios and relative efficiencies have been measured for a variety of -ray energies. These measurements were used to validate a GEANT4 simulation of the TIGRESS detectors, which was then used to create a simulation of the full 12-detector array. Predictions of the expected performance of TIGRESS are presented. These predictions indicate that TIGRESS will be capable, for single 1MeV rays, of absolute detection efficiencies of 17% and 9.4%, and peak-to-total ratios of 54% and 61% for the “high-efficiency” and “optimized peak-to-total” configurations of the array, respectively. [Copyright &y& Elsevier]

Abstract: Reports that incident photons near 10keV can induce the emission of gamma rays with concomitant energy release from the 31-year isomer of 178Hf challenge established models of nuclear and atomic physics. In order to provide a direct and independent assessment of these claims, a multi-detector system was designed as a specialized research tool. The YSU miniball is unique in its combination of performance characteristics, compact size and portability, enabling it to be easily transported to and placed within the confines of beamline hutches at synchrotron radiation sources. Monochromatic synchrotron radiation was used in the most recent studies from which evidence of prompt triggering was claimed, suggesting similar sites for independent tests of these results. The miniball array consists of six high-efficiency BGO scintillators coupled with a single 65% Ge detector and provides time-resolved gamma-ray calorimetry rather than purely spectroscopic data. The need to record high detected folds from the array (up to seven-fold gamma coincidences) makes this system different in practice from standard spectroscopic arrays for which data is typically restricted to triples or lower folds. Here the system requirements and design are discussed, as well as system performance as characterized using the well-known natural decay cascades of 178m2Hf. This serves as the foundation for subsequent high-sensitivity searches for low-energy triggering of gamma emission from this isomer. [Copyright &y& Elsevier]

Abstract: Sensitivity to the locations of -ray interactions within a 32-fold segmented clover-type HPGe detector has been investigated through Compton scattering of -rays from a collimated source. A mean position sensitivity of 0.44mm at an energy of 373keV is deduced by comparing the average pulse shapes for net charge collecting signals, as well as transient induced signals in neighbouring contacts, from 1007 pairs of three-dimensionally localized interaction points. The reconstruction of individual event locations based on a comparison with the measured set of basis waveforms is presented. [Copyright &y& Elsevier]