Positron Decays ofTi42andCa38

The positron decay of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ti}$ has been investigated using the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}(h, n)$ reaction with a natural calcium target. A strong 610.7±0.5-keV $\gamma$ ray with a half-life $T_{\frac{1}{2}}=0.202\mathrm{}\pm 0.005$ sec is attributed to a positron branch to the 611-keV level of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Sc}$. A weak 2222±2-keV $\gamma$ ray has been observed, which corresponds to a positron branch to the 2223-keV level of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Sc}$. Using this measured half-life and the $\beta$-decay energies, the branching ratios are calculated from $\beta$-decay systematics to be ${r_{\beta 0}}^{+}=(44.1\mathrm{}\pm 1.2)\%$, ${r_{\beta 1}}^{+}=(55.2\mathrm{}\pm 1.2)\%$, and ${r_{\beta 9}}^{+}=(0.7\mathrm{}\pm 0.3)\%$. The $log\mathrm{ft}$ values 3.179±0.015 and ${4.36}_{-0.24\mathrm{}}^{+0.16\mathrm{}}$ establish $J^{\pi }=1^{+}$ for both the 611- and the 2223-keV states of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Sc}$. The positron decay of ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$ has been investigated using the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}(h, n)$ reaction. The half-life 0.439±0.012 sec has been measured for this decay. In addition to the strong Gamow-Teller transition feeding the 1695-keV level of ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$, a weak 3210±2-keV $\gamma$-ray line has been observed which is tentatively attributed to a transition from the 3337-keV level in ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$ fed by a (0.6±0.2)% ${\beta }^{+}$ branch of ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$. Its $log\mathrm{ft}$ (${3.90}_{-0.13\mathrm{}}^{+0.10\mathrm{}}$) then establishes the $J^{\pi }=1^{+}$ assignment for this state.