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Register a new userProperties of 187Ta revealed through isomeric decay
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Mass-separated 187Ta in a high-spin isomeric state has been produced for the first time by multi-nucleon transfer reactions, employing an argon gas stopping cell and laser ionisation. Internal gamma rays revealed a 7.3 s isomer at 1778 keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer decay reduced E2 hindrance factor of 27 supports the interpretation that axial symmetry is approximately conserved.
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We report the independent experimental confirmation of an isomeric state in the proton drip-line nucleus $^{26}$P. The ${gamma}$-ray energy and half-life determined are 164.4 $pm$ 0.3 (sys) $pm$ 0.2 (stat) keV and 104 $pm$ 14 ns, respectively, which are in agreement with the previously reported values. These values are used to set a semi-empirical limit on the proton separation energy of $^{26}$P, with the conclusion that it can be bound or unbound.
The isomeric and {beta} decays of the N = Z +2 nucleus 96Ag were investigated at NSCL. A cascade of {gamma}-ray transitions originating from the de-excitation of a {mu}s isomer was observed for the first time and was found in coincidence with two previously-known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) {mu}s, more precise than previously reported. The existence of a second, longer-lived {mu}s isomer, associated with a 743-keV transition, is also proposed here. Shell model results within the (p_{3/2}p_{1/2}f_{5/2}g_{9/2}) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.
Neutron-rich nuclei were populated in a relativistic fission of 238U. Gamma-rays with energies of 135 keV and 184 keV were associated with two isomeric states in 121Pd and 117Ru. Half-lives of 0.63(5) microseconds and 2.0(3) micrisecondss were deduced and the isomeric states were interpreted in terms of deformed single-particle states.
The ground-state properties of neutron-rich 106Nb and its beta decay into 106Mo have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a 252Cf fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN beta-decay-spectroscopy station. The measured 106Nb ground-state mass excess of -66202.0(13) keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, beta-decaying state in 106Nb above 5 keV in excitation energy. The decay half-life of 106Nb was measured to be 1.097(21) s, which is 8% longer than the adopted value. The level scheme of the decay progeny, 106Mo, has been expanded up to approximately 4 MeV. The distribution of decay strength and considerable population of excited states in 106Mo of J >= 3 emphasises the need to revise the adopted Jpi = 1- ground-state spin-parity assignment of 106Nb; it is more likely to be J => 3.
The $beta$-decay properties of the neutron-deficient nuclei $^{25}$Si and $^{26}$P have been investigated at the GANIL/LISE3 facility by means of charged-particle and $gamma$-ray spectroscopy. The decay schemes obtained and the Gamow-Teller strength distributions are compared to shell-model calculations based on the USD interaction. B(GT) values derived from the absolute measurement of the $beta$-decay branching ratios give rise to a quenching factor of the Gamow-Teller strength of 0.6. A precise half-life of 43.7 (6) ms was determined for $^{26}$P, the $beta$- (2)p decay mode of which is described.
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