Nuclear spectroscopy with lithium beams. II. High-spin states inCr52,Mn54,Fe54, andFe56

The nuclei ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ have been investigated using ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ bombardment of ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ at about 25 MeV bombarding energy. Further information has been obtained on the nuclei ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$ and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ from the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ bombardment of ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ at the same energy. Experimental methods used included recoil distance lifetime measurements (RDM), $\gamma -\gamma$ coincidence measurements, angular distribution measurements, and Doppler shift attenuation lifetime measurements (DSAM) on $\gamma$ rays from high spin states in the various nuclei. Mean lifetimes determined by RDM were as follows: in ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, 3114-keV level ($\tau =60.0\mathrm{}\pm 2.6$ psec); in ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, 156-keV level ($\tau ={278}_{-120\mathrm{}}^{+40\mathrm{}}$ psec); 368 keV (10.4 ± 1.6 psec); 1073 keV (292 ± 50 psec); in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, 847-keV level ($\tau =7.9\mathrm{}\pm 1.2$ psec). Tentative spin assignments were made as follows: in ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, 4751-keV level, $J=\left(8\right)\mathrm{}$ (this state can be identified with the seniority 4, $J^{\pi }=8^{+}$ state predicted in this region); in ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, 1073-keV level $J=\left(6\right)\mathrm{}$; in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, 3389-keV level $J=\left(6\right)\mathrm{}$. Decay schemes observed in these nuclei are presented. Lifetimes (or limits) were also established from DSAM measurements for a number of other levels in these nuclei. Recent shell model calculations for these nuclei are discussed.