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In this work we present the results from two experiments dedicated to search for quadrupolecollective isovector valence-shell excitation, the states with so-called mixed proton-neutron symmetry (MSS), in nuclei around the doubly magic nucleus 208Pb. 212Po was studied in an α-transfer reaction. 204Hg was studied in an inverse kinematics Coulomb excitation reaction on a carbon target. Both experiments provide indications for existence of one-phonon MSSs. Those are the first experimentally identified MSSs in the mass A ≈ 208 region.

A program of high-precision half-life and branching-ratio measurements for superallowed Fermi β emitters is being carried out at TRIUMF’s Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14O, 18Ne, and 26Alm, as well as branching-ratio measurements for 26Alm and 74Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi β decays.

The lifetimes of the $ 2^+_1$ , the $ 2^+_2$ and the $ 3^-_1$ states of Po have been measured in the Pb(C,Be)Po transfer reaction by the Doppler-shift attenuation method. The result for the lifetime of the $ 2^+_1$ state is about three times shorter than the adopted value. However, the new value still does not allow for a consistent description of the properties of the yrast $ 2^+_1$ , $ 4^+_1$ , $ 6^+_1$ , and $ 8^+_1$ states of Po in the framework of nuclear shell models. Quasi-particle Phonon Model (QPM) calculations also cannot overcome this problem thus indicating the existence of a peculiarity which is neglected in both theoretical approaches. [ABSTRACT FROM AUTHOR]

States in 26Na were populated in the (d, pγ) reaction, induced by bombarding deuterium target nuclei with an intense reaccelerated beam of 25Na ions from the ISAC2 accelerator at TRIUMF. Gamma-rays were recorded in coincidence with protons and used to extract differential cross sections for 21 states up to the neutron decay threshold of 5 MeV. Results for levels below 3 MeV are discussed in detail and compared with shell model calculations and with previous work. The angular distributions of decay gamma-rays were measured for individual states and are compared to theoretically calculated distributions, highlighting some issues for future work. [ABSTRACT FROM AUTHOR]

The highly-efficient and segmented TIGRESS y-ray spectrometer at TRIUMF has been used to perform a reorientation-effect Coulomb-excitation study of the 2+ state at 3.368 MeV in l0Be. This is the first Coulomb-excitation measurement that enables one to obtain information on diagonal matrix elements for such a high-lying first excited state from y-ray data. With the availability of accurate lifetime data, a value of --0.110 ± 0.087 eb is determined for the 〈2+1||Ê2||2+1|〉 diagonal matrix element, which assuming the rotor model, leads to a negative spectroscopic quadrupole moment of Qs(2+1) = --0.083 ± 0.066 eb. This result is in agreement with both no-core shell-model calculations performed in this work with the CD-Bonn 2000 two-nucleon potential and large shell-model spaces, and Green's function Monte Carlo predictions with two- plus three-nucleon potentials. [ABSTRACT FROM AUTHOR]

We present the results from an experiment dedicated to search for quadrupole-collective isovector valence-shell excitations, states with so-called mixed proton-neutron symmetry (MSS), of 212Po. This nucleus was studied in an α-transfer reaction. The lifetimes of two short-lived excited states, candidates for the one-phonon MSS, were determined by utilizing the Doppler shift attenuation method. The experimental results are in qualitative agreement with a simple single-j shell model calculation, which, together with the observed lack of quadrupole collectivity, indicates that the isovector nature of low-lying states is a property of the leading single-particle valence shell configuration. [ABSTRACT FROM AUTHOR]

Abstract: The first measurement of inelastic scattering of 9Li from deuterons at the ISAC facility is reported. The measured angular distribution for the first excited state confirms the nature of excitation to be an E2 transition. The quadrupole deformation parameter is extracted from an analysis of the angular distribution. [Copyright &y& Elsevier]

Background: Nuclei in the A " 190 mass region show gradual shape changes from prolate through nonaxial deformed shapes and ultimately towards spherical shapes as the Pb region is approached. Exploring how this shape evolution occurs will help us understand the evolution of collectivity in this region. Purpose: The level scheme of the 192 Au nucleus in A "190 region was studied in order to deduce its deformations. Methods: High-spin states of 192Au have been populated in the 186W("B, 5n) reaction at a beam energy of 68 MeV and their ? decay was studied using the YRAST Ball detector array at the Wright Nuclear Structure Laboratory (WNSL), Yale University. Results: Based on double and triple ?-ray coincidence data the level scheme of 192 Au has been extended up to Ip = 32+ at an excitation energy of ~6 MeV. Conclusion: The results are discussed in the framework of pairing and deformation self-consistent total Routhian surface (TRS) and cranked shell model (CSM) calculations. The comparison of the experimental observations with the calculations indicates that this nucleus takes a nonaxial shape similar to other Au nuclei in this region. [ABSTRACT FROM AUTHOR]

We report a precise determination of the 19Ne half-life to be T1/2 = 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. [ABSTRACT FROM AUTHOR]

High-spin properties of the nucleus 117Hf were studied through the 128Te(48Ca,5n) reaction. Previously known bands have been extended to significantly higher spins and four new bands have been extracted from these data. The results are discussed within the framework of the cranked shell model aided by a comparison with level structures in the neighboring nuclei. The band crossings at rotational frequencies ∼500 keV are interpreted as caused by the alignments of h11/2 and h9/2 proton Orbitals. Band ED2 exhibits an alignment pattern similar to that of band EDI which was reported in a recent paper and proposed to be built on a second potential energy minimum involving the deformation-driving proton i13/2 ⊗ h19/2 configuration. It is likely that band ED2 is also associated with a deformation enhanced with respect to that of the normal deformed structures. Further experimental investigation is needed to ascertain the nature of this band. [ABSTRACT FROM AUTHOR]

A high-precision branching-ratio measurement for the superallowed ß+ emitter 26Alm was performed at the TRIUMF-ISAC radioactive ion beam facility. An upper limit of <12 ppm at 90% confidence level was found for the second forbidden yS+ decay of 26Alm to the 2 state at 1809 keV in 26Mg. An inclusive upper limit of 15 ppm at 90% confidence level was found when considering all possible nonanalog jö+/EC decay branches of 26 Alm, resulting in a superallowed branching ratio of 100.0000+0-0.0015 %. [ABSTRACT FROM AUTHOR]

The level scheme of 18176Os has been investigated with the 150Nd(36S,5n) reaction. The low-K rotational bands built upon the 9/2+[624], 7/2−[514] and 1/2−[521] neutron configurations have been extended and other new bands established. The configurations of these low-K bands are discussed within the framework of the cranked-shell model. The lifetimes for some of the states in the 9/2+[624] and 1/2−[521] collective rotational bands were also measured using the Doppler Shift Attenuation method. The large deformations deduced are found to be consistent with those predicted from theoretical Total Routhian Surface calculations. These results support the idea that for these low-K states the nuclear shape is axially symmetric and allows the K quantum number to be defined and the associated K-selection rule to be upheld. This behaviour apparently contrasts with that of the higher-K states in 181Os. In the higher-spin regime, two new high-K intrinsic states, with Kπ=37/2+ and Kπ=41/2+, were established, along with the fragmented decay of a Kπ=33/2− intrinsic state. The configurations and excitation energies of these experimentally determined intrinsic states are found to be in excellent agreement with theoretical calculations based on a fixed shape Nilsson model plus BCS pairing. The structures on top of these intrinsic states do, however, show very different behaviour. A relatively regular high-K rotational band was observed on top of the Kπ=41/2+ state but not for the other newly-established intrinsic states. Theoretical configuration-constrained potential energy surface calculations suggest that the irregular transition sequence above the Kπ=37/2+ intrinsic bandhead state, the limited excitations observed above the other intrinsic states and the observation of fragmented and non-hindered decays, are due to these configurations being subject to an appreciable γ softness. These calculations reveal that the Kπ=41/2+ configuration is less susceptible to distortions in the γ plane than any of the other high-K states. [Copyright &y& Elsevier]