Yrast states inFe52,Mn52and the decay ofFem52

The properties of yrast states of $^{52}\mathrm{Fe}$ and $^{52}\mathrm{Mn}$ were studied using the $^{40}\mathrm{Ca}$ + $^{14}\mathrm{N}$ reaction. In-beam $\ensuremath{\gamma}$-ray singles, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence, and $n\ensuremath{-}\ensuremath{\gamma}$ coincidence data establish the positions of the lowest ${2}^{+}$ and ${4}^{+}$ states of $^{52}\mathrm{Fe}$ as 849.1\ifmmode\pm\else\textpm\fi{}0.3 and 2384.6\ifmmode\pm\else\textpm\fi{}0.7 keV, respectively. No $\ensuremath{\gamma}$ rays associated with other $^{52}\mathrm{Fe}$ states could be found. This is because an $^{52}\mathrm{Fe}$ isomer at 6.83 MeV ${\ensuremath{\beta}}^{+}$ decays to $^{52}\mathrm{Mn}$, diverting strength from the $^{52}\mathrm{Fe}$ $\ensuremath{\gamma}$ cascade. Delayed $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data give information on the high-spin yrast states of $^{52}\mathrm{Mn}$ populated in the ${\ensuremath{\beta}}^{+}$ decay of the isomer. The results are consistent with several recently published works, and unambiguously establish that the $^{52}\mathrm{Mn}$ ${8}^{+}$ state is at 2286.0\ifmmode\pm\else\textpm\fi{}0.4 keV. The delayed spectra show no indication of direct $\ensuremath{\gamma}$ decay of the $^{52}\mathrm{Fe}$ isomer. An upper limit on the $\ensuremath{\gamma}$ decay branch is 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$. On the basis of the ${(1{f}_{\frac{7}{2}})}^{n}$ model with "bare" nucleon charges, direct $E4$ $\ensuremath{\gamma}$ emission should be the dominant decay mode. It is argued that the absence of $E4$ decay, taken together with known $B(E4)$ data on $^{44}\mathrm{Sc}$, $^{52}\mathrm{Mn}$ and $^{53}\mathrm{Fe}$, shows $E4$ effective charges in the ($1{f}_{\frac{7}{2}}$) shell are different for nuclei located near the beginning or end of the shell. Further, the effective charges near the end of the shell seem to be quite different from those found in $E2$ transitions, i.e., ${e}_{p}\ensuremath{\sim}0.5$, ${e}_{n}\ensuremath{\sim}\ensuremath{-}0.5$. First order perturbation calculations in the ${(1f,2p)}^{n}$ model offer qualitative, but not quantitative, insight as to the $E4$ effective charge behavior.RADIOACTIVITY $^{52}\mathrm{Fe}^{m}$; measured ${T}_{\frac{1}{2}}$. $\ensuremath{\beta}\ensuremath{\gamma}$ coin., $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ coin; deduced $log\mathrm{ft}$, $E4$ limit. $^{52}\mathrm{Mn}$ deduced levels.NUCLEAR REACTIONS $^{40}\mathrm{Ca}$($^{14}\mathrm{N}$, $\mathrm{np}$)$^{52}\mathrm{Fe}$, $E=29 \mathrm{to} 38$ MeV; measured prompt $\ensuremath{\gamma}$ and $n\ensuremath{\gamma}$ coinc., deduced $^{52}\mathrm{Fe}$ levels.