Level Structure ofSn118andSn120from the Decay of Sb Isotopes

The decay of 5-hr ${\mathrm{Sb}}^{118}$ and 6-day ${\mathrm{Sb}}^{120}$ were studied. The spins, parities, and multipole orders of the transitions in both Sn isotopes are characterized by $7-\left(E2\mathrm{}\right)5-\left(E1\mathrm{}\right)4+\left(E2\mathrm{}\right)2+\left(E2\mathrm{}\right)0+$. Level ordering in both isotopes was determined to differ from the previously accepted order. The spins and multipole order assignments were determined from angular correlation and internal conversion measurements in ${\mathrm{Sn}}^{118}$ and from a reinterpretation of similar experimental results by Ikegami for ${\mathrm{Sn}}^{120}$. All $\beta$ decay is directly to the 7- states. The levels are at 2.57, 2.32, 2.28, and 1.23 Mev in ${\mathrm{Sn}}^{118}$ and 2.50, 2.30, 2.21, and 1.18 Mev in ${\mathrm{Sn}}^{120}$. Half-lives determined using delayed coincidence techniques were as follows: (7-), (2.3±0.1)×${10}^{-7\mathrm{}}$ sec; (5-), (2.0±0.3)×${10}^{-8\mathrm{}}$ sec in ${\mathrm{Sn}}^{118}$; and (7-), (1.12±0.10)×${10}^{-5\mathrm{}}$ sec; (5-), (5.2±0.4)×${10}^{-9\mathrm{}}$ sec in ${\mathrm{Sn}}^{120}$. Reduced transition probabilities are compared with current theories. No crossover transitions were found in either decay except for a weak 1.090-Mev $E3\mathrm{}$ transition from the 5- to 2+ levels in ${\mathrm{Sn}}^{118}$, which has a reduced transition probability close to single-particle speed. Triple coincidence experiments determined a ${\beta }^{+}$ to capture ratio of (1.6±0.1)×${10}^{-3\mathrm{}}$ in the ${\mathrm{Sb}}^{118}$ decay yielding an inferred transition energy of 1.32 Mev.