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Register a new userSpectroscopic study of $^{47}$Ca from the $beta^-$ decay of $^{47}$K
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The $beta^-$ decay of $^{47}$K to $^{47}$Ca is an appropriate mechanism for benchmarking interactions spanning the $sd$ and $pf$ shells, but current knowledge of the $beta^-$-decay scheme is limited. We have performed a high-resolution, high-efficiency study of the $beta^-$-decay of $^{47}$K with the GRIFFIN spectrometer at TRIUMF-ISAC. The study revealed 48 new transitions, a more precise value for the $^{47}$K half-life (17.38(3)~s), and new spin and parity assignments for eight excited states. Levels placed for the first time here raise the highest state observed in $beta^-$ decay to within 568(3) keV of the $Q$-value and confirm the previously measured large $beta^-$-decay branching ratios to the low-lying states. Previously unobserved $beta^-$-feeding to 3/2$^+$ states between 4.5 and 6.1~MeV excitation energy was identified with a total $beta^-$-feeding intensity of 1.29(2)%. The sum of the $B(GT)$ values for these states indicates that the $1s_{1/2}$ proton hole strength near this excitation energy is comparable to the previously known $1s_{1/2}$ proton and neutron hole strengths near 2.6 MeV.
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We report on high-statistics data from the $beta^-$ decay of the $^{46}$K $J^{pi}$ = 2$^-$ ground state taken with the GRIFFIN spectrometer located at the TRIUMF-ISAC facility. In total, 199 $gamma$ rays and 42 excited states were placed in the level scheme, and from the observed $beta$ feeding and angular correlations of pairs of cascading $gamma$ rays, it was possible to assign spins and parities to excited states and determine mixing ratios for selected $gamma$ rays. The level structure of $^{46}$Ca is compared to theoretical predictions from a microscopic valence-space Hamiltonian derived from two- (NN) and three-nucleon (3N) forces. These calculations are in reasonable agreement with the experimental data and indicate that the protons in this region are not as inert as would be expected for semi-magic nuclei.
$^{48}$Ca, the lightest double beta decay candidate, is the only one simple enough to be treated exactly in the nuclear shell model. Thus, the $betabeta(2 u)$ half-life measurement, reported here, provides a unique test of the nuclear physics involved in the $betabeta$ matrix element calculation. Enriched $^{48}$Ca sources of two different thicknesses have been exposed in a time projection chamber, and yield T$_{1/2}^{2 u} = (4.3^{+2.4}_{-1.1} [{rm stat.}] pm 1.4 [{rm syst.}]) times 10^{19}$ years, compatible with the shell model calculations.
High signal-to-noise integrated spectra of the metal-rich globular cluster 47 Tuc, spanning the H-gamma(HR) and Fe4668 line indices, have been obtained. The combination of these indices has been suggested (Jones & Worthey 1995, ApJ, 446, L31) as the best available mechanism for cleanly separating the age-metallicity degeneracy which hampers the dating of distant, unresolved, elliptical galaxies. For the first time, we apply this technique to a nearby spheroidal system, 47 Tuc, for which independent ages, based upon more established methods, exist. Such an independent test of the techniques suitability has not been attempted before, but is an essential one before its application to more distant, unresolved, stellar populations can be considered valid. Because of its weak series of Balmer lines, relative to model spectra, our results imply a spectroscopic ``age for 47 Tuc well in excess of 20 Gyr, at odds with the colour-magnitude diagram age of 14+/-1 Gyr. The derived metal abundance, however, is consistent with the known value. Emission ``fill-in of the H-gamma line as the source of the discrepancy cannot be entirely excluded by existing data, although the observational constraints are restrictive.
A beta-decay study of Cu-77 has been performed at the ISOLDE mass separator with the aim to deduce its beta-decay properties and to obtain spectroscopic information on Zn-77. Neutron-rich copper isotopes were produced by means of proton- or neutron-induced fission reactions on U-238. After the production, Cu-77 was selectively laser ionized, mass separated and sent to different detection systems where beta-gamma and beta-n coincidence data were collected. We report on the deduced half-live, decay scheme, and possible spin assignment of 77Cu.
The $beta$-decay and isomeric properties of $^{54}$Sc, $^{50}$K and $^{53}$Ca are presented, and their implications with respect to the goodness of the N=32 sub-shell closure discussed.
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