A new isomeric level at 561 keV [$T_{\frac{1}{2}}=87\mathrm{}\left(2\right)\mathrm{}$ nsec] in ${}_{}{}^{72}{}_{}{}^{}\mathrm{As}$ has been excited by the reaction ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, 2pn){}_{}{}^{72}{}_{}{}^{}\mathrm{As}$ using pulsed beams of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$. The spin-precession of this level has been observed in cobalt, and also, after recoil implantation, in nickel. The $g$ factor is measured to be $g=+0.116\mathrm{}\left(2\right)\mathrm{}$, which yields +274(7) kG for $B_{\mathrm{hf}}\left(\mathrm{As}\mathit{Co}\right)$.

NUCLEAR REACTIONS Pulsed beam: ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, 2pn)$; observed isomeric level; measured $T_{\frac{1}{2}}$, spin-precession in Co, Ni; deduced $g$, $B_{\mathrm{hf}}$.

• Received 20 December 1976

DOI:https://doi.org/10.1103/PhysRevC.15.1583