Decay ofAr41

A weak gamma ray has been found in the decay of ${\mathrm{Ar}}^{41}$ to ${\mathrm{K}}^{41}$. The energy of the gamma ray is 1.664±0.007 MeV; and its intensity, relative to that of the strong 1.293-MeV gamma ray, is (5±2)×${10}^{-4\mathrm{}}$. It is concluded from the results of conincidence measurements that this gamma ray is the result of a beta-ray branch from ${\mathrm{Ar}}^{41}$ leading to an excited state in ${\mathrm{K}}^{41}$ at 1.664 MeV. The associated $log\mathrm{ft}$ value is found to be 7.7±0.3. The spin and parity of the 1.664-MeV state in ${\mathrm{K}}^{41}$ are most probably ${\frac{5}{2}}^{+}$ or ${\frac{7}{2}}^{+}$.