Levels ofSi29below 4.1-MeV Excitation Energy

Abstract

The states of ${\mathrm{Si}}^{29}$ at 1.28-, 2.03-, 2.43-, 3.07-, 3.62-, and 4.08-MeV have been studied using the particle-$\ensuremath{\gamma}$ angular-correlation method of Litherland and Ferguson. The ${\mathrm{Si}}^{28}(d, p){\mathrm{Si}}^{29}$ reaction was used to populate the levels of ${\mathrm{Si}}^{29}$ at several bombarding energies in the neighborhood of 3 MeV. Charged particles were detected near 180\ifmmode^\circ\else\textdegree\fi{} with respect to the incident-beam direction in a solid-state annular counter, and $\ensuremath{\gamma}$ radiation was detected in a 10.2\ifmmode\times\else\texttimes\fi{}10.2 cm NaI(Tl) crystal at angles between 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} relative to the incident-beam direction. The $p\ensuremath{-}\ensuremath{\gamma}$ coincident data were stored in a 2-parameter pulse-height analyzer. $\ensuremath{\gamma}$-ray branching ratios derived from these data are presented for the levels mentioned above. In addition to an independent confirmation of the spin assignments $\frac{3}{2}$, $\frac{5}{2}$, and $\frac{3}{2}$ for the ${\mathrm{Si}}^{29}$ levels at 1.28-, 2.03-, and 2.43-MeV, respectively, an assignment $J=\frac{7}{2}$ for the 3.62-MeV level and a most probable assignment $J=\frac{5}{2}$ for the 3.07-MeV level are established. For the 4.08-MeV level, $J\ensuremath{\ge}\frac{3}{2}$. Some $\ensuremath{\gamma}$-ray mixing ratios are also presented, and an upper limit for the mean lifetime, ${\ensuremath{\tau}}_{m}\ensuremath{\le}{90}^{\ensuremath{-}8}$ sec, was obtained for all the levels studied.