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Register a new userBeta decay of Neutron-Rich 53-56Ca
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Beta-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for 54Ca [86(7) ms], 55Ca [22(2) ms], and 56Ca [11(2) ms]. The half-life of 230(6) ms deduced for 53Ca is significantly longer than reported previously, where the decay chain 53K -> 53Ca -> 53Sc was considered. A delayed gamma ray with energy 247 keV as identified following beta decay of 54Ca, and is proposed to depopulate the first 1+ level in 54Sc. The beta-decay properties compare favorably with the results of shell model calculations completed in the full pf-space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross beta-decay theory. The systematic trend of the neutron-rich Ca half-lives is consistent with the presence of a subshell gap at N=32.
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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.
The $beta$-decay half-lives of 55 neutron-rich nuclei $^{134-139}$Sn, $^{134-142}$Sb, $^{137-144}$Te, $^{140-146}$I, $^{142-148}$Xe, $^{145-151}$Cs, $^{148-153}$Ba, $^{151-155}$La were measured at the Radioactive Isotope Beam Factory (RIBF) employing the projectile fission fragments of $^{238}$U. The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly-measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of $r$ process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second ($A$ $approx$ 130) peak.
Precision measurements in neutron beta decay serve to determine the coupling constants of beta decay and allow for several stringent tests of the standard model. This paper discusses the design and the expected performance of the Nab spectrometer.
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 of neutron-rich $^{129}$In into $^{129}$Sn was studied using the GRIFFIN spectrometer at the ISAC facility at TRIUMF. The study observed the half-lives of the ground state and each of the $beta$-decaying isomers. The level scheme of $^{129}$Sn has been expanded with thirty-one new $gamma$-ray transitions and nine new excited levels, leading to a re-evaluation of the $beta$-branching ratios and level spin assignments. The observation of the $beta$-decay of the (29/2$^{+}$) 1911-keV isomeric state in $^{129}$In is reported for the first time, with a branching ratio of 2.0(5)$%$.
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