Search

In recent years, the exploitation of the iecoil-decay tagging (RDT) technique with,large arrays of germanium detectors has revealed much information about the structure of heavy nuclei approaching the proton drip line. The yrast bands of the N

Several nuclei in the A ∼ 190 region have been studied following deep-inelastic reactions using a 460 MeV 82 Se projectile impinging upon a thick 192 Os target. The GASP array (at the Legnaro National Laboratory in Italy) was used to measure the resulting γ-decays. The previously reported near-yrast structure of 191 Os is extended to a t 1 /2= 61 ns isomer, at an energy of 2640 keV. Branching ratios for ΔI = 1 and A/ = 2 transitions in the K π = 11/2 + band have been measured, giving |(g K - g R )/Q 0 | = 0.022(3) and 0.024(7) for transitions from the 17/2 + and (19/2 + ) states respectively. These are consistent with the theoretical calculation for the proposed v11/2 + [615] configuration of the band. Nilsson plus BCS calculations reveal that the isomer is likely to have a {v11/2 + [615] ⊗ π11/2-[505] ⊗ π9/2-[514]} configuration with J π = K π = 31/2 + . This yields an implied reduced hindrance of f v = 1.9, in accordance with empirical systematics of K isomers in the A ∼ 180-190 region.

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 world's most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

BaF 2 detectors for picosecond gamma-ray decay lifetime measurements have been installed into the 8π gamma-ray spectrometer as a proof-of-principle for a possible installation of a full array of ten detectors. Using four detectors a test measurement of the half-life of the 2 + state in 152 Sm resulted in a value of 1.33(6) ns, compared with a published value of 1.396 ns. Measurements with a 26 Na stopped beam were performed with various master-trigger conditions. Using a master trigger of germanium-SCEPTAR-BaF 2 OR BaF 2 -BaF 2 , the FWHM of the BaF 2 -BaF 2 triggered events was found to be ∼290 ps compared with ∼ 1.9 ns for the germanium-SCEPTAR-BaF 2 triggered events. Simulations using GEANT4 of a suggested BaF 2 lifetime measurement system have been carried out. These illustrate the considerable gain in spectrum quality which can be expected using simple add-back protocols.

The 8 pi spectrometer, installed at the TRIUMF-ISAC facility, was the world's 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.

The Di-pentagonal Array for Nuclear Timing Experiments (DANTE) is an array of ten BaF2 detectors used in conjunction with the 8π gamma-ray spectrometer at the TRIUMF-ISAC radioactive-ion beam facility. DANTE is used to conduct direct lifetime measurements of nuclear excited states in the picosecond - nanosecond range. This, in turn, will aid in probing the collective structures of deformed nuclei. The capability of DANTE to measure nanosecond-scale lifetimes is demonstrated by using a 152Eu source. The half-life of the Iπ = 21+ state of 152Sm is measured to be 1.426 ± 0.018 ns.