Half-lives and branchings forβ-delayed neutron emission for neutron-rich Co–Cu isotopes in ther-process

Abstract

The β-decays of very neutron rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL β-counting station in conjunction with the neutron detector NERO. We measured the branchings for β-delayed neutron emission (Pn values) for 74 Co (18±15%), and 75−77 Ni (10±2.8%, 14±3.6%, and 30±24%, respectively) for the first time, and remeasured the Pn values of 77−79 Cu, 79,81 Zn, and 82 Ga. For 77−79 Cu and for 81 Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75 Co (30±11 ms) and 80 Cu (170 +110 −50 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron capture process (r-process) is explored. We find that with our new data the classical rprocess model is better able to reproduce the A = 78 − 80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino driven high entropy winds in core collapse supernovae.

βdecay of nuclei around90Se: Search for signatures of aN=56subshell closure relevant to theQuinn1, Aprahamian2, Pereira3 et al. 2012Phys. Rev. CSelf Cite

“…The speed of the r-process reaction sequence and the resulting abundances of the elements are significantly influenced by the β-decay properties of the nuclei involved, which are in turn directly related to the evolution of nuclear structure and deformation. In a recent measurement of the half life of the doubly-magic nucleus 78 Ni [8,9], it was shown that the persistence of the closed neutron and proton shells had a significant impact on the r-process abundance patterns, and theoretical predictions for the half life were significantly longer than observed.…”

“…The results are used as a nuclear-structure probe to study the deformation of the β-decay mother/daughter system, which in turn can provide first hints of the underlying shell structure (see for instance Refs. [9,[16][17][18][19][20]). …”

Impact of Nuclear Mass Uncertainties on therProcess

“…Some studies show that neutron star mergers provide an important contribution to the solar system rprocess, but this is not enough to explain the abundances in the oldest observed stars, see e.g., [12][13][14]. In contrast, other models can explain the r-process abundances at all metallicities solely based on the neutron star merger scenario [15].Experimentally, there has been impressive progress in approaching r-process nuclei, see [16][17][18][19][20][21] and references quoted therein. New-generation radioactive ion beam facilities [22][23][24] will be able to reach a range of nuclei…”

“…Experimentally, there has been impressive progress in approaching r-process nuclei, see [16][17][18][19][20][21] and references quoted therein. New-generation radioactive ion beam facilities [22][23][24] will be able to reach a range of nuclei never possible before, including the neutron-rich frontier of the nuclear landscape.…”

Novel technique for Constrainingr-Process (n,γ) Reaction Rates

“…A large effort has been devoted to the measurement of masses, β -decay half-lives, and β -delayed neutron emission probabilities (e.g. recently [3][4][5]), however, the majority of the r-process nuclei are still not accessible. In addition, although in many environments the neutron-capture reaction rates do not play significant role in the r-process flow due to (n, γ)-(γ, n) equilib- * spyrou@nscl.msu.edu † liddick@nscl.msu.edu ‡ a.c.larsen@fys.uio.no rium, recent studies have shown significant sensitivity to the neutron-capture reaction rates in certain conditions [6].…”