Beta-decay half-lives of new neutron-rich chromium-to-nickel isotopes and their consequences for the astrophysical r-process

Calculation of beta-decay properties of neutron-rich nickel isotopes

“…While with the use of the -on the average -distinctly shorter T1/2 of [11] in an explosive He-burning scenario [29] considerable improvement over earlier attempts could be obtained as far as the reproduction of positions and relative heights of the r-abundance peaks at A ~ 130 and 195 are concerned [32], difficulties were met in the region around A=80 [12,33]. These calculations showed that, when starting from the Fe group seed nuclei, not even the N = 50 shell (corresponding to the A ~ 80 abundance peak) could be reached during the short duration of the neutron flux of a few tenths of a second in explosive He-burning, and solar-system r-abundances could not be re-produced anymore (see also [34]).…”

“…3.3, the amount of neutron branching close to the N=50 magic shell, and in particular sudden jumps in P~. of neighbouring nuclei, may be of interest for the interpretation of the 'r-abundance puzzle' in the A-~ 80 mass region [12,27,28].…”

“…These features may already be hidden in the Tx/2 of 24Cr to 2sNi isotopes with (N-Z)> 10 which are up to an order of magnitude shorter than the two available predictions [10,11]. As far as astrophysics is concerned, a general trend towards short T~/2 up to the neutron drip line in the Fe group region would be of importance for calculations of rapid neutroncapture (r-process) nucleosynthesis (see, e.g., [12,13]). …”

βdecay of71,73Co: Probing single-particle states approaching doubly magic78<

“…In addition to the nuclear structure motivated study, 78 Ni is also of interest to nuclear astrophysics [12,17]. Theoretical models of the astrophysical rapid neutron capture process (r-process) [18][19][20] predict a bottleneck around 78 Ni before continuing on and ultimately leading to the creation of heavier elements.…”

Discovery of the cobalt isotopes

“…"The 0.4 sec activity can be tentatively assigned to 64 Co since its β end point energy of 7.0±0.5 MeV is within reasonable agreement with the estimate of 7.5 MeV by Yamada and Matumoto." This half-life agrees with the currently adopted value of 0.30(3) s. Previously, several measurements of different incorrect half-life measurements were reported, for example, 4-5 m by Parmley et al [38], 2.0(2) m and 7.8(2) m for the ground and an isomeric state, respectively by Preiss and Fink [42], and 28 (2) 66 Co and 67 Co in 1985 as described in Beta-decay half-lives of new neutronrich chromium-to-nickel isotopes and their consequences for the astrophysical r-process [44]. 76 Ge was accelerated to 11.4 MeV/u at GSI and bombarded a natural tungsten target.…”