The 23-MeV proton beam from the Michigan State University sector-focused cyclotron was used to produce the ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ isotope by means of the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}\mathrm{}(p,n)\mathrm{}{}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ reaction. From measurements of $\gamma$ rays following the positron decay of ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$, the half-life of ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ was measured to be 0.265±0.025 sec, and energy levels in ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ were measured at 1.9701±0.0007, 4.1779±0.0007, 4.4401±0.0012, and 6.6119±0.0009 MeV. The 6.6119-MeV level is identified as the $T=1\mathrm{}$ analog of the ground states of ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$ and ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$. Branching ratios for the positron decay of ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ were obtained and the $log\mathrm{ft}$ values computed for each branch, using the observed partial half-life and a computed value of the ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ mass. Spin and parity assignments of 2+ have been made for the ground state of ${}_{}{}^{36}{}_{}{}^{}\mathrm{K}$ and the $T=1\mathrm{}$ level of ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$, in agreement with the expectation from the previously measured 2+ value of the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$ ground-state spin.

• Received 12 September 1966

DOI:https://doi.org/10.1103/PhysRev.153.1165