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A program of high-precision superallowed Fermi β decay studies is being carried out at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. Recent high-precision branching ratio measurements for the superallowed decays of 74Rb and 26Alm, as well as a half-life measurement for 26Alm that is the most precise half-life measurement for any superallowed emitter to date, are reported. These results provide demanding tests of the theoretical isospin symmetry breaking corrections in superallowed Fermi β decays. [ABSTRACT FROM AUTHOR]

The TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer (TIGRESS) is a state-of-the-art γ-ray spectrometer being constructed at the ISAC-II radioactive ion beam facility at TRIUMF. TIGRESS will be comprised of twelve 32-fold segmented high-purity germanium (HPGe) clover-type γ-ray detectors, with BGO/CsI(Tl) Compton-suppression shields, and is currently operational at ISAC-II in an early-implementation configuration of six detectors. Results have been obtained for the first experiments performed using TIGRESS, which examined the A = 20, 21, and 29 isotopes of Na by Coulomb excitation. [ABSTRACT FROM AUTHOR]

The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186–192Os as Kπ = 4+ two-phonon vibrations, whereas inelastic scattering, and (t,α) work imply a hexadecapole phonon description. To clarify the nature of these Kπ = 4+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets using 30 MeV 3He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5° to 50°. Results indicate a significant 52+[402]π+32+[402]π component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure. [ABSTRACT FROM AUTHOR]

Levels in 186,188Os have been investigated using the (3He,d) reaction with 30 MeV 3He beams. Absolute level-population cross sections have been determined, and angular distributions measured between 5° and 50°. The 43+ levels are observed to be some of the strongest populated states below 2 MeV excitation energy, and the magnitudes of the 5/2+[402]π+3/2+[402]π configuration extracted are in line with quasiparticle-phonon model predictions which state that the lowest-lying Kπ = 4+ band is predominantly a hexadecapole excitation. [ABSTRACT FROM AUTHOR]

High-spin states in 3674Kr38 were studied using the 40Ca(40Ca,α2p)74Kr fusion evaporation reaction at a beam energy of 165 MeV with GAMMASPHERE and MICROBALL and at a beam energy of 185 MeV with EUROBALL and ISIS multi-detector arrays. Lifetimes of the high-spin states for the ground-state band and the favoured negative-parity band have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments show a marginal decrease as a function of spin, suggesting that the rotational bands do not terminate at the maximum spin Imax. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A measurement of the ground state β-decay branching ratio of 62Ga has been made as part of a program of high-precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by detecting γ rays and β particles from the decay of 62Ga using the 8π γ-ray spectrometer and the SCEPTAR plastic scintillator array. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The 8π spectrometer at TRIUMF-ISAC consists of 20 Compton-suppressed germanium detectors and various auxiliary devices. The Ge array, once used for studies of nuclei at high angular momentum, has been transformed into the world’s most powerful device dedicated to radioactive-decay studies. Many improvements in the spectrometer have been made, including a high-throughput data acquisition system, installation of a moving tape collector, incorporation of an array of 20 plastic scintillators for β-particle tagging, 5 Si(Li) detectors for conversion electrons, and 10 BaF2 detectors for fast-lifetime measurements. Experiments can be performed where data from all detectors are collected simultaneously, resulting in a very detailed view of the nucleus through radioactive decay. A number of experimental programmes have been launched that take advantage of the versatility of the spectrometer, and the intense beams available at TRIUMF-ISAC. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fragmentation reactions, typically performed at energies ∼E/A > 50 MeV, produce neutron-rich nuclei but leave little angular momentum in the residues. In this work we have examined the product distribution and angular momentum input for a 12C beam at 30 MeV/A on a thick (40 mg/cm2) target of 51V, testing the feasibility of in-beam gamma-ray spectroscopy study of target fragments at this lower energy. This technique allows the study of some neutron-rich nuclei to moderate spins, complementing the beam fragmentation studies. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have performed three separate experiments at LBNL’s 88-Inch Cyclotron over a period of several years in which 235U (thick target) was Coulomb-excited. It involved stand-alone experiments with Gammasphere and with the 8PI Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with an 40Ar beam at 180 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases ( e.g. [631]1/2, [624]7/2 and [622]5/2) strongly populated by E3 excitation. The CHICO data has been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many E1 and M1 matrix elements could be extracted from the γ-ray branching ratios. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recent experiments with GAMMASPHERE and the MICROBALL charged-particle detector array have led to the identification, and have enabled the detailed spectroscopic study, of highly-deformed and superdeformed rotational bands in a number of A ∼ 40, N ≈ Z nuclei. These rotational bands are built on multi-particle multi-hole excitations across the N, Z = 20 shell gap from the sd to the pf shell and, in the context of the Nilsson scheme, are associated with the shell gaps formed at large prolate deformation for particle numbers N, Z = 16, 18,20 as pf-shell intruder orbitals are occupied. In analogy with well-developed rotational motion in heavy nuclei, these highly collective rotational structures involve active valence particles in two major shells for both protons and neutrons, yet the A ∼ 40 bands possess the unique advantage that the valence space dimension remains small enough to be approached from a shell-model perspective. These rotational bands thus provide an ideal opportunity for detailed comparisons between experimental data and both microscopic and macroscopic models of collective motion in nuclei. [ABSTRACT FROM AUTHOR]

High-spin states have been studied in [sup 72,73]Kr using [sup 40]Ca+[sup 40]Ca and [sup 36]Ar+[sup 40]Ca reactions at 160, 164 and 145 MeV respectively. The properties and configurations of the bands observed are interpreted with the aid of unpaired cranked Nilsson-Strutinsky/cranked relativistic mean-field calculations and paired total routhian surface and cranked relativistic Hartree-Bogoliubov calculations. In [sup 73]Kr the three previously known structures have been extended to a spin of ∼30h and a fourth structure, which is believed to be the signature partner to the g[sub 9/2] band, has been identified. The negative parity bands show evidence for an unusual type of band crossing. It is currently unclear whether this is a consequence of T=0 n-p pairing. At the highest spins the unpaired calculations can reproduce the observed data, suggesting that there is little evidence for pairing correlations in this spin regime. In [sup 72]Kr a new band has been identified that has the properties expected from the missing doubly aligned S-band configuration. The properties of this band can be reproduced by the unpaired CNS/CRMF calculations, again suggesting that the structure has little pairing. However, paired calculations appear to be necessary to reproduce the properties of the previously known structure in this nucleus. The [sup 72]Kr results are also compared with projected shell model calculations. [ABSTRACT FROM AUTHOR]

High-spin states in [sup 108]Cd were studied following the reaction [sup 64]Ni([sup 48]Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structures e.g. in the A ≈ 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the πi[sub 13/2] hyper-intruder orbital is occupied in these newly observed bands. [ABSTRACT FROM AUTHOR]

We have studied the continuous gamma radiation from reactions of [sup 48]Ca beams on targets of [sup 50]Ti, [sup 64]Ni, [sup 96]Zr, and [sup 124]Sn at very high angular momentum. In all but the heaviest target, the nuclear moments of inertia rise rapidly with increasing angular momentum and the data suggest that the gamma ray energies may reach a maximum value. Whether this arises from a gradual transition towards a highly deformed Jacobi-like shape, or from other effects, is unclear. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intrinsic quadrupole moment Q[sub 0] of superdeformed rotational bands in A∼150 nuclei depends on the associated single-particle configuration. We have derived an empirical formula based on the additivity of effective quadrupole moments of single-particle orbitals that describes existing measurements from [sup 142]Sm to [sup 152]Dy. To further test the formula, the predicted Q[sub 0] moments for two superdeformed bands in [sup 146]Gd of 14.05 eb were confronted with a new measurement yielding 13.9±0.4 eb and 13.9±0.3 eb respectively. This excellent agreement provides empirical evidence of extreme single-particle behavior in highly deformed, collective systems. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In response to new opportunities presented by re-accelerated beams from the ISAC-II facility at TRIUMF, a plunger-type Recoil Distance Method device, the TIGRESS Integrated Plunger, is under construction to be used with the TIGRESS segmented germanium array. An experimental program aimed in nuclear structure measurements along the N=Z line is planned. Lifetime measurements in the shape-coexistence region near N∼Z∼36 are anticipated to provide information of significance to Vud matrix element evaluation from superallowed beta-decay measurements. [ABSTRACT FROM AUTHOR]

The present work reports on the 76195Os isotope, which is the most neutron-rich osmium isotope for which transitions have been measured. It has been populated following a multi-nucleon transfer reaction between a thin 78198Pt target and an 850-MeV 54136Xe beam. Evidence from γ-ray coincidences has been found for an Iπ = (27/2-) isomeric state with a measured half-life of 26±9ns. [ABSTRACT FROM AUTHOR]