G. Hackman

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.

Radioactive beam experiments with large gamma-ray detector arrays

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.

High-resolution γ-ray spectroscopy: a versatile tool for nuclear β-decay studies at TRIUMF-ISAC

High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the worlds most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

SHARC: Silicon Highly-segmented Array for Reactions and Coulex used in conjunction with the TIGRESS γ-ray spectrometer

The combination of γ-ray spectroscopy and charged-particle spectroscopy is a powerful tool for the study of nuclear reactions with beams of nuclei far from stability. This paper presents a new silicon detector array, SHARC, the Silicon Highly-segmented Array for Reactions and Coulex. The array is used at the radioactive-ion-beam facility at TRIUMF (Canada), in conjunction with the TIGRESS γ-ray spectrometer, and is built from custom Si-strip detectors utilising a fully digital readout. SHARC has more than 50% efficiency, approximately 1000-strip segmentation, angular resolutions of Δθ ≈ 1.3 deg and Δ ≈ 3.5 deg, 25–30 keV energy resolution, and thresholds of 200 keV for up to 25 MeV particles. SHARC is now complete, and the experimental program in nuclear astrophysics and nuclear structure has commenced.

Lifetime of 19 Ne * (4.03 MeV)

The Doppler-shift attenuation method was applied to measure the lifetime of the 4.03 MeV state in {sup 19}Ne. By utilizing a {sup 3}He-implanted Au foil as a target, the state was populated using the {sup 20}Ne({sup 3}He, {alpha}){sup 19}Ne reaction in inverse kinematics at a {sup 20}Ne beam energy of 34 MeV. De-excitation {gamma} rays were detected in coincidence with {alpha} particles. At the 1{sigma} level, the lifetime was determined to be 11{sub -3}{sup +4} fs and at the 95.45% confidence level the lifetime is 11{sub -7}{sup +8} fs.

High-precision measurement of the 19Ne half-life and implications for right-handed weak currents.

We report a precise determination of the (19)Ne half-life to be T(1/2)=17.262±0.007 s. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.

Far from 'Easy' Spectroscopy with the 8π and GRIFFIN Spectrometers at TRIUMF-ISAC

The 8 pi spectrometer, installed at the TRIUMF-ISAC facility, was the worlds most sensitive gamma-ray spectrometer dedicated to beta-decay studies. A description is given of the 8 pi spectrometer and its auxiliary detectors including the plastic scintillator array SCEPTAR used for beta-particle tagging and the Si(Li) array PACES for conversion electron measurements, its moving tape collector, and its data acquisition system. The recent investigation of the decay of Cs-124 to study the nuclear structure of Xe-124, and how the beta-decay measurements complemented previous Coulomb excitation studies, is highlighted, including the extraction of the deformation parameters for the excited 0(+) bands in Xe-124. As a by-product, the decay scheme of the (7(+)) Cs-124 isomeric state, for which the data from the PACES detectors were vital, was studied. Finally, a description of the new GRIFFIN spectrometer, which uses the same auxiliary detectors as the 8 pi spectrometer, is given.

Two-neutron transfer reaction mechanisms in 12 C(6 He, 4 He) 14 C using a realistic three-body 6 He model

The reaction mechanisms of the two-neutron transfer reaction 12C(6He,4He) have been studied at Elab=30 MeV at the TRIUMF ISAC-II facility using the Silicon Highly-segmented Array for Reactions and Coulex (SHARC) charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 2+2 8.32 MeV state in 14C, using a realistic three-body 6He model and advanced shell-model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30-MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at Elab=18 MeV, however, is not as well described by the same reaction model, suggesting that one needs to include higher-order effects in the reaction mechanism.

Towards 26Na via (d,p) with SHARC and TIGRESS and a novel zero-degree detector

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus 26Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×107 pps of 25Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD)2 target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction.

Precision half-life measurement of 62Ga

A measurement of the half-life of 62Ga was made as part of a programme of high-precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by counting β+ particles from the decay of 62Ga in a 4π gas proportional counter. The half-life was measured to be 116.01 ± 0.19 ms. Several parameters were varied during the experiment to test for systematic effects, but no significant effects were found.