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Register a new userEvidence for a beta-decaying 1/2- isomer in 71Ni
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We report on the investigation of the population mechanism for the 454-KeV level in 71Cu. This level was identified for the first time in a recent Coulomb excitation measurement with a radioactive beam of 71Cu. The selective nature of the Coulomb-excitation process as well as nuclear-structure considerations constrain the possible spin values for the newly observed state to Ipi=1/2-. A re-examination of the data set obtained in a beta-decay study at the LISOL separator revealed that this state is also populated in the decay of 71Ni, most probably by direct feeding from a newly identified 1/2- beta-decaying isomer having a T1/2=2.34(25) s. In this paper we investigate the proposed scenario by reanalyzing the beta-gamma and gamma-gamma coincidences obtained in the beta-decay study at LISOL.
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The decay of odd-odd $^{150}$Pm has been studied by populating the nucleus with the $^{150}$Nd(p,n)$^{150}$Pm reaction at E$_{beam}$ = 8.0 MeV using 97$%$ enriched $^{150}$Nd target. The presence of an isomeric state with $beta$ decay half life of 2.2(1) h could be identified in $^{150}$Pm by following the half lives of the observed $gamma$ transitions. The decay of the isomer to the excited levels of $^{150}$Sm has been confirmed by observing the $gamma - gamma$ coincidence with the VENUS array of six Compton suppressed Clover HPGe detectors. The $beta$ decay end-point energies corresponding to the decay from the $^{150g}$Pm and $^{150m}$Pm have been measured using a $beta-gamma$ coincidence setup of two thin window Planar HPGe detectors and four Clover HPGe detectors of the VENUS array. The systematics of the similar isomeric states in neighboring nuclei has been studied to understand the underlying structure of these states. Shell model calculation has been performed by using OXBASH code which indicates the presence of a 5$^-$ isomeric state at very low excitation in the nucleus. The calculation also suggests hindered electromagnetic decay of this isomer and supports the possibility of its $beta$ decay to the excited levels of $^{150}$Sm.
Background: The evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the `southwest region of $^{78}$Ni, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. Purpose: We intend to measure the isomeric and $beta$ decay of $^{75}$Co, with one-proton and two-neutron holes relative to $^{78}$Ni, to access new nuclear structure information in $^{75}$Co and its $beta$-decay daughters $^{75}$Ni and $^{74}$Ni. Methods: The nucleus $^{75}$Co is produced in relativistic in-flight fission reactions of $^{238}$U at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and $beta$ decay are studied exploiting the BigRIPS and EURICA setups. Results: We obtain partial $beta$-decay spectra for $^{75}$Ni and $^{74}$Ni, and report a new isomeric transition in $^{75}$Co. The energy [$E_{gamma}=1914(2)$ keV] and half-life [$t_{1/2}=13(6)$ $mu$s] of the delayed $gamma$ ray lend support for the existence of a $J^{pi}=(1/2^-)$ isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in $^{75}$Ni, but the first calculated $1/2^-$ level in $^{75}$Co, a prolate $K=1/2$ state, is predicted about 1 MeV below the observed $(1/2^-)$ level. Conclusions: The spherical-like structure of the lowest-lying excited states in $^{75}$Ni is proved. In the case of $^{75}$Co, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below $^{78}$Ni. Further experimental efforts to discern the nature of the $J^{pi}=(1/2^-)$ isomer are necessary.
We report the first observation of the 2$^+$ isomer in $^{52}$Co, produced in the $beta$ decay of the 0$^+$, $^{52}$Ni ground state. We have observed three $gamma$-rays at 849, 1910, and 5185 keV characterizing the $beta$ de-excitation of the isomer. We have measured a half-life of 102(6) ms for the isomeric state. The Fermi and Gamow-Teller transition strengths for the $beta$ decay of $^{52m}$Co to $^{52}$Fe have been determined. We also add new information on the $beta$ decay of the 6$^+$, $^{52}$Co ground state, for which we have measured a half-life of 112(3) ms.
Collinear laser spectroscopy has been performed on the $^{79}_{30}$Zn$_{49}$ isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life was confirmed, and the nuclear spins and moments of the ground and isomeric states in $^{79}$Zn as well as the isomer shift were measured. From the observed hyperfine structures, spins $I = 9/2$ and $I = 1/2$ are firmly assigned to the ground and isomeric states. The magnetic moment $mu$ ($^{79}$Zn) = $-$1.1866(10) $mu_{rm{N}}$, confirms the spin-parity $9/2^{+}$ with a $ u g_{9/2}^{-1}$ shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment $mu$ ($^{79m}$Zn) = $-$1.0180(12) $mu_{rm{N}}$ supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the $N = 50$ shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state: $delta langle r^{2}_{c}rangle^{79,79m}$ = +0.204(6) fm$^{2}$, providing first evidence of shape coexistence.
The neutron rich nucleus $^{193}$Os was produced in the $^{192}$Os($^{7}$Li,$^{6}$Li)$^{193}$Os reaction. An isomeric state based on the $9/2^-$[505] nilsson orbital was identified in the present work. Half-life of the isomeric state was extracted and discussed in terms of the $K$ quantum number. Level scheme built on the isomeric state was proposed based on the experimental data.
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