Isobaric Analog States inCl35

Abstract

The $\gamma$-ray yield from the ${\mathrm{S}}^{34}(p, \gamma ){\mathrm{Cl}}^{35}$ reaction shows strong resonances at proton energies of 1214 and 1512 keV. These resonance states occur at the correct energies to be isobaric analogs of the 1.99- and 2.35-MeV states in ${\mathrm{S}}^{35}$, respectively. Angular-distribution, triple-correlation, and polarization measurements have been performed at each of these resonances. The 1214-keV resonance, which corresponds to an excitation energy of 7.54 MeV in ${\mathrm{Cl}}^{35}$, has spin and parity of ${\frac{7}{2}}^{-}$, and decays almost entirely to the 3.16-MeV level, which was also found to have spin and parity of ${\frac{7}{2}}^{-}$. The transition is pure Ml and has a measured strength of 1.6±0.3 Weisskopf units (W.u.). The 1512-keV resonance, which corresponds to an excitation energy of 7.84 MeV, has a spin and parity of ${\frac{3}{2}}^{-}$, and decays strongly to the 4.17-MeV level, which was found to be a ${\frac{3}{2}}^{-}$ state. This transition is also pure Ml with a strength of 1.0±0.3 W.u. The value of ${{\theta }_p}^2$ is about 0.2 for both the 1214-keV and the 1512-keV resonance, which compares favorably with the value of ${{\theta }_p}^2=\frac{1}{3}$ calculated for the pure single-nucleon $f_{\frac{7}{2}}$, $T=\frac{3}{2}$ and $p_{\frac{3}{2}}$, $T=\frac{3}{2}$ configurations respectively. This agrees with the large ($d, p$) stripping width of the analog states at 1.99 and 2.35 MeV in ${\mathrm{S}}^{35}$. The levels at 3.16 and 4.17 MeV appear to be of the same configuration as the corresponding resonance states, and to differ only in isobaric spin, having $T=\frac{1}{2}$. Values for the reduced widths, energies, and isobaric-spin splitting of the $T_{>}$ and $T_{<}$ states, and for the Ml transition speeds assuming pure single-nucleon states, have been calculated and are in good agreement with observed values.