α-cluster excited states in 32 S

The β decay of 100 Tc has been studied by using the total absorption γ -ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. In this work the new Decay Total Absorption γ -ray Spectrometer in coincidence with a cylindrical plastic β detector has been employed. The β intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double β decay of 100 Mo.

Section: A Description Of Nuclear Modelmentioning

confidence: 99%

Experimental study of Tc100 β decay with total absorption γ -ray spectroscopy

Guadilla¹,

Algora²,

Taín³

et al. 2017

“…More details of the calculation scheme are given in Ref. [27]. For the normal (particle-hole) part of the EDF, I employed mainly the SkM* functional [28] and secondarily the SLy4 functional [29].…”

Section: B Numerical Calculationsmentioning

confidence: 99%

Suddenly shortened half-lives beyond Ni78:N=50 magic number and high-energy nonunique first-forbidden transitions

Yoshida

2019

Background: β-decay rates play a decisive role in understanding the nucleosynthesis of heavy elements and are governed by microscopic nuclear-structure information. A sudden shortening of the half-lives of Ni isotopes beyond N = 50 was observed at the RIKEN-RIBF. This is considered due to the persistence of the neutron magic number N = 50 in the very neutron-rich Ni isotopes. Purpose: By systematically studying the β-decay rates and strength distributions in the neutronrich Ni isotopes around N = 50, I try to understand the microscopic mechanism for the observed sudden shortening of the half-lives. Methods: The β-strength distributions in the neutron-rich nuclei are described in the framework of nuclear density-functional theory. I employ the Skyrme energy-density functionals (EDF) in the Hartree-Fock-Bogoliubov calculation for the ground states and in the proton-neutron Quasiparticle Random-Phase Approximation (pnQRPA) for the transitions. Not only the allowed but the firstforbidden (FF) transitions are considered. Results: The experimentally observed sudden shortening of the half-lives beyond N = 50 is reproduced well by the calculations employing the Skyrme SkM* and SLy4 functionals in contrast to the monotonic shortening predicted in the preceding calculation using the SkO' functional. Conclusions: The sudden shortening of the half-lives beyond N = 50 in the neutron-rich Ni isotopes is due to the shell gap at N = 50 and cooperatively with the high-energy transitions to the low-lying 0 − and 1 − states in the daughter nuclei. The onset of FF transitions pointed out around N = 82 and 126 is preserved in the lower-mass nuclei around N = 50. This study suggests that needed is a microscopic calculation where the shell structure in neutron-rich nuclei and its associated effects on the FF transitions are selfconsistenly taken into account for predicting β-decay rates of exotic nuclei in unknown region.

“…1 presents also the ISM results of [40] (red horizontal bars), the pnQRPA results of [36] (thin black vertical bars), and the pnQRPA results of [41,42] (thick green vertical bars). The cross inside a circle presents the result g eff A = 0.293 of a ββ analysis of 128 Te using the microscopic interacting boson-fermion model (IBFFM-2) [46]. …”

Section: Theoretical Backgroundmentioning

confidence: 99%

Impact of the quenching of gA on the sensitivity of 0νββ experiments

Suhonen

2017

Detection of the neutrinoless ββ (0νββ) decay is of high priority in the particle-and neutrinophysics communities. The detectability of this decay mode is strongly influenced by the value of the weak axial-vector coupling constant gA. The recent nuclear-model analyses of β and ββ decays suggest that the value of gA could be dramatically quenched, reaching ratios of g free A /gA ≈ 4, where g free A = 1.27 is the free, neutron-decay, value of gA. The effects of this quenching appear devastating for the sensitivity of the present and future 0νββ experiments since the 4th power of this ratio scales the 0νββ half-lives. This, in turn, could lead to some two orders of magnitude less sensitivity for the 0νββ experiments. In the present article it is shown that by using a consistent approach to both the two-neutrino ββ and 0νββ decays by the proton-neutron quasiparticle random-phase approximation (pnQRPA), the feared two-orders-of-magnitude reduction in the sensitivity of the 0νββ experiments actually shrinks to a reduction by factors in the range 2 − 6. This certainly has dramatic consequences for the potential to detect the 0νββ decay.PACS numbers: 21.60.Jz, 23.40.Hc, 27.50.+e, 27.60.+j Keywords: Detectability of the neutrinoless double beta decay, nuclear matrix elements, quenching of the axial-vector coupling strength, sensitivity of the double-beta experiments