The new isotope ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ was produced via the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}({}_{}{}^{11}{}_{}{}^{}\mathrm{B},pn){}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ reaction at $E\left({}_{}{}^{11}{}_{}{}^{}\mathrm{B}\right)=21\mathrm{}$ MeV. Delayed singles $\gamma$ spectra, and $\gamma -\gamma$ and $\beta -\gamma$ coincidences were measured, using large Ge(Li) detectors and a plastic scintillator. The half-life of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ was measured to be 21.1 ± 1.0 s, and its ground-state spin and parity have been assigned as 3/$2^{-}$. Spin restrictions have been placed on a number of levels in the daughter nucleus ${}_{}{}^{57}{}_{}{}^{}\mathrm{Mn}$. The mass excess of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ was determined to be -52.39 ± 0.10 MeV. The measured ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ mass excess is compared with various predictions.

RADIOACTIVITY ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cr}$ [from ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}({}_{}{}^{11}{}_{}{}^{}\mathrm{B},pn)$]; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $\gamma -\gamma$ coin, $E_{\beta }$, $\beta -\gamma$ coin; deduced decay scheme, $log\mathrm{ft}$ values, $J^{\pi }$, mass excess. ${}_{}{}^{57}{}_{}{}^{}\mathrm{Mn}$ deduced levels, $J^{\pi }$ restrictions. Enriched targets, multiple rabbit, helium jet, Ge(Li) and plastic detectors.

• Received 3 January 1978

DOI:https://doi.org/10.1103/PhysRevC.17.1815