9 research outputs found
Shell model calculation of the beta- and beta+ partial halflifes of 54Mn and other unique second forbidden beta decays
The nucleus 54Mn has been observed in cosmic rays. In astrophysical
environments it is fully stripped of its atomic electrons and its decay is
dominated by the beta- branch to the 54Fe ground state. Application of 54Mn
based chronometer to study the confinement of the iron group cosmic rays
requires knowledge of the corresponding halflife, but its measurement is
impossible at the present time. However, the branching ratio for the related
beta+ decay of 54Mn was determined recently. We use the shell model with only a
minimal truncation and calculate both beta+ and beta- decay rates of 54Mn. Good
agreement for the beta+ branch suggests that the calculated partial halflife of
the beta- decay, (4.94 \pm 0.06) x 10^5 years, should be reliable. However,
this halflife is noticeably shorter than the range 1-2 x 10^6 y indicated by
the fit based on the 54Mn abundance in cosmic rays. We also evaluate other
known unique second forbidden beta decays from the nuclear p and sd shells
(10Be, 22Na, and two decay branches of 26Al) and show that the shell model can
describe them with reasonable accuracy as well.Comment: 4 pages, RevTeX, 2 figure
Excited States in 52Fe and the Origin of the Yrast Trap at I=12+
Excited states in 52Fe have been determined up to spin 10\hbar in the
reaction 28Si + 28Si at 115 MeV by using \gamma-ray spectroscopy methods at the
GASP array. The excitation energy of the yrast 10+ state has been determined to
be 7.381 MeV, almost 0.5 MeV above the well known \beta+-decaying yrast 12+
state, definitely confirming the nature of its isomeric character. The mean
lifetimes of the states have been measured by using the Doppler Shift
Attenuation method. The experimental data are compared with spherical shell
model calculations in the full pf-shell.Comment: 9 pages, RevTeX, 7 figures include