[en] The 8π γ-ray spectrometer has been used to resolve high-spin states in the nucleus ⁵⁶Fe following the reaction ⁴⁸Ca(¹³C,5n)⁵⁶Fe at a beam energy of 65 MeV. This study has extended the known decay scheme of ⁵⁶Fe to J^π=(13⁺)ℎ. The experimental decay scheme is compared with theoretical shell model calculations within the pf shell valence space

[en] High-spin states in the N=Z nucleus ⁷²Kr have been populated in the ⁴⁰Ca(⁴⁰Ca, 2α)⁷²Kr fusion-evaporation reaction at a beam energy of 165 MeV and using a thin isotopically enriched ⁴⁰Ca target. The experiment, performed at Argonne National Laboratory close to Chicago, USA, employed the Gammasphere array for γ-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in ⁷²Kr were extended to a higher excitation energy of ∼24 MeV and higher angular momentum of 30ℎ. Using the Doppler-shift attenuation method, the lifetimes of high-spin states were measured for the first time in order to investigate deformation changes associated with the g_9/2 proton and neutron alignments in this N=Z nucleus. An excellent agreement with theoretical calculations including only standard t=1 np pairing was observed

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[en] High-resolution gamma-ray spectroscopy is essential to fully exploit the unique scientific opportunities at the next generation radioactive ion beam facilities such as the TRIUMF Isotope Separator and Accelerator (ISAC). At ISAC the 8π spectrometer and its associated auxiliary detectors is optimize for β-decay studies while TIGRESS an array of segmented clover HPGe detectors has been designed for studies with accelerated beams. This paper gives a brief overview of these facilities and also presents recent examples of the diverse experimental program carried out at the 8π spectrometer.

[en] A high-precision branching ratio measurement for the superallowed β⁺ decay of ⁶²Ga was performed at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. The 8π spectrometer, an array of 20 high-purity germanium detectors, was employed to detect the γ rays emitted following Gamow-Teller and nonanalog Fermi β⁺ decays of ⁶²Ga, and the SCEPTAR plastic scintillator array was used to detect the emitted β particles. Thirty γ rays were identified following ⁶²Ga decay, establishing the superallowed branching ratio to be 99.858(8)%. Combined with the world-average half-life and a recent high-precision Q-value measurement for ⁶²Ga, this branching ratio yields an ft value of 3074.3±1.1 s, making ⁶²Ga among the most precisely determined superallowed ft values. Comparison between the superallowed ft value determined in this work and the world-average corrected Ft value allows the large nuclear-structure-dependent correction for ⁶²Ga decay to be experimentally determined from the CVC hypothesis to better than 7% of its own value, the most precise experimental determination for any superallowed emitter. These results provide a benchmark for the refinement of the theoretical description of isospin-symmetry breaking in A≥62 superallowed decays

[en] The stable Cd isotopes have long been used as paradigms for spherical vibrational motion. Extensive investigations with in-beam γ spectroscopy have resulted in very-well-established level schemes, including many lifetimes or lifetime limits. A programme has been initiated to complement these studies with very-high-statistics β decay using the 8π spectrometer at the TRIUMF radioactive beam facility. The decays of ¹¹²In and ¹¹²Ag have been studied with an emphasis on the observation of, or the placement of stringent limits on, low-energy branches between potential multi-phonon levels. A lack of suitable 0⁺ or 2⁺ three-phonon candidates has been revealed. Further, the sum of the B(E2) strength from spin 0⁺ and 2⁺ states up to 3 MeV in excitation energy to the assigned two-phonon levels falls far short of the harmonic-vibrational expectations. This lack of strength points to the failing of collective models based on vibrational phonon structures.

[en] Excitations in 94Ru were populated through the β+/ε decay of 94Rh following the fusion evaporation reaction 58Ni(40Ca,3pn)94Rh. Recoiling nuclei were implanted on the Yale moving tape collector at the Wright Nuclear Structure Laboratory, and delayed γ-rays were observed via an array of four Compton suppressed HPGe clover detectors. Nine new γ-transitions and five new levels were added to the level scheme of (π1g(9/2))Jπ=6+4 level, in close agreement with prediction

[en] The half-life of the superallowed β⁺ emitter ⁶²Ga has been measured at TRIUMF's Isotope Separator and Accelerator facility using a fast-tape-transport system and 4π continuous-flow gas proportional counter to detect the positrons from the decay of ⁶²Ga to the daughter ⁶²Zn. The result, T_1/2=116.100±0.025 ms, represents the most precise measurement to date (0.022%) for any superallowed β-decay half-life. When combined with six previous measurements of the ⁶²Ga half-life, a new world average of T_1/2=116.121±0.021 ms is obtained. This new half-life measurement results in a 20% improvement in the precision of the ⁶²Ga superallowed ft value while reducing its mean by 0.9σ to ft=3074.3(12) s. The impact of this half-life measurement on precision tests of the CVC hypothesis and isospin symmetry breaking corrections for A≥62 superallowed decays is discussed

[en] The branching ratio for the superallowed β⁺ decay of ³⁸K^m was measured at TRIUMF's ISAC radioactive ion beam facility. The M3 internal transition between the isomer and the ground state of ³⁸K^m was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue β-decay branch to the first excited 0⁺ state in ³⁸Ar was also performed and yielded an upper limit of ≤12 ppm at 90% C.L. These measurements lead to a revised superallowed branching ratio for ³⁸K^m of 99.967(4)%, and increase the ³⁸K^m ft value by its entire quoted uncertainty to ft=3052.1(10) s. Implications for tests of the nuclear-structure dependent corrections in superallowed β decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element V_ud are discussed