Cross-shell excited configurations in the structure of Si34

The cross-shell excited states of Si34 have been investigated via β decays of the 4- ground state and the 1+ isomeric state of Al34. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder 1+ isomeric state of Al34, intruder levels of Si34 are populated via allowed β decays. Spin assignments to such intruder levels of Si34 were established through γ-γ angular correlation analysis for the negative-parity states with dominant configurations (νd3/2)-1⊗ - (νf7/2)1 as well as the positive-parity states with dominant configurations (νsd)-2⊗ - (νf7/2p3/2)2. The configurations of such intruder states play crucial roles in our understanding of the N=20 shell gap evolution. A configuration interaction model derived from the FSU Hamiltonian was utilized in order to interpret the intruder states in Si34. Shell model interaction derived from a more fundamental theory with the valence space in medium similarity renormalization group method was also employed to interpret the structure of Si34

High-precision half-life determination of 14^{14}O via direct ββ counting

The half-life of the superallowed Fermi $\beta^+$ emitter $^{14}$O was determined to high precision via a direct $\beta$ counting experiment performed at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF. The result, $T_{1/2}$($^{14}$O) = 70619.2(76) ms, is consistent with, but is more precise than, the world average obtained from 11 previous measurements. Combining the $^{14}$O half-life deduced in the present work with the previous most precise measurements of this quantity leads to a reduction in the overall uncertainty, by nearly a factor of 2. The new world average is $T_{1/2}$($^{14}$O) = 70619.6(63) ms with a reduced $\chi^2$ value of 0.87 obtained from 8 degrees of freedom

Configuration mixing investigation in germanium isotopes through measurement of E0 transition strengths

Experimental and theoretical studies of the germanium isotopes on the neutron-rich side of the stability valley point increasingly toward the emergence of triaxiality, configuration mixing, and shape coexistence phenomena. Studies of the E0 strengths, which can provide a direct measure of the amount of configuration mixing, are lacking. Thus, determining E0 transition strengths is essential for an understanding of the evolution of structures in the Ge isotopes. Beta-decay experiments populating excited states in the 72,74,76,78Ge isotopes were performed at the TRIUMF-ISAC radioactive beam facility. Gamma-ray and electron spectroscopic investigations have been performed, to measure E0 strengths between states of J > 0, exploiting the GRIFFIN spectrometer combined with the PACES silicon detector array. Preliminary results from this study are presented

Decay spectroscopy of Eu160: Quasiparticle configurations of excited states and structure of Kπ=4+ bandheads in Gd160

Background: Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the r-process path and following freeze-out region impact the resulting r-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei. Purpose: We aim to improve the understanding of the nuclear structure of Gd160, specifically the Kπ=4+ bands, as well as study the β decay of Eu160 into Gd160. Methods: High-statistics decay spectroscopy of Gd160 resulting from the β-decay of Eu160 was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility. Results: Two new excited states and ten new transitions were observed in Gd160. The β-decaying half-lives of the low- and high-spin isomers in Eu160 were determined, and the low-spin state's half-life was measured to be t1/2=26.0(8) s, ≈16% shorter than previous measurements. Lifetimes of the two Kπ=4+ bandheads in Gd160 were measured for the first time, as well as γ-γ angular correlations and mixing ratios of intense transitions out of those bandheads. Conclusions: Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the Kπ=4+ bandheads in Gd160 is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0-keV state in Gd160 heavily populated in β decay is shown to have positive parity, which raises questions regarding the structure of the high-spin β-decaying state in Eu160