Gamma-Ray Transitions inA=35Nuclei

Abstract

The mean lifetime of the 1.99-MeV ${\frac{7}{2}}^{\ensuremath{-}}$ level of ${\mathrm{S}}^{35}$ was determined by a measurement of the delayed coincidence between protons and $\ensuremath{\gamma}$ rays in the reaction ${\mathrm{S}}^{34}(d,p\ensuremath{\gamma}){\mathrm{S}}^{35}$ at ${E}_{d}=4.48$ MeV, with the result ${\ensuremath{\tau}}_{m}=1.47\ifmmode\pm\else\textpm\fi{}0.07$ nsec. The $\ensuremath{\gamma}$ decay of the ${\frac{7}{2}}^{\ensuremath{-}}$, $T=\frac{3}{2}$ analog of this level at ${E}_{x}=7.55$ MeV in ${\mathrm{Cl}}^{35}$ was examined in detail with large-volume Ge(Li) detectors and Ge(Li)-NaI(Tl) coincidence techniques. The $\ensuremath{\gamma}$-ray spectra obtained at the analog state, which appears as a well-known resonance at ${E}_{p}=1211$ keV in the reaction ${\mathrm{S}}^{34}(p,\ensuremath{\gamma}){\mathrm{Cl}}^{35}$, revealed the presence of several previously unknown transitions in addition to the known strong analog-to-antianalog $M1$ transition to the ${\frac{7}{2}}^{\ensuremath{-}}$, $T=\frac{1}{2}$ level at 3.16 MeV. Examples are a crossover $M2$ transition from the analog resonance to the ${\frac{3}{2}}^{+}$ ground state of ${\mathrm{Cl}}^{35}$ with a strength of 3.0 \ifmmode\pm\else\textpm\fi{} 0.8 Weisskopf units, a mixed $E1\ensuremath{-}M2$ transition ($\ensuremath{\delta}=0.44\ifmmode\pm\else\textpm\fi{}0.12$) from the ${\frac{7}{2}}^{\ensuremath{-}}$ antianalog state to the ${\frac{5}{2}}^{+}$ level at 1.76 MeV, and a 160-keV transition between the antianalog state and the ${\frac{5}{2}}^{+}$ level at 3.00 MeV. Weak transitions which can be interpreted as members of cascades through levels in the region ${E}_{x}=4.3\ensuremath{-}5.7$ MeV were also identified. It is shown that the $M1$, $E2$, $M2$, and $E3$ strengths of transitions connecting members of the system of parent, analog, antianalog, and ground states can be accurately reproduced by a simple model based upon an inert ${\mathrm{S}}^{32}$ core with active nucleons in the ${d}_{\frac{3}{2}}$ and ${f}_{\frac{7}{2}}$ orbits, with bare-nucleon $g$ factors for the magnetic transitions, and with reasonable effective charges for the electric transitions. The wave functions for the ${\frac{7}{2}}^{\ensuremath{-}}$ levels derived from this model are used to predict strengths of mirror transitions in ${\mathrm{Ar}}^{35}$ and ${\mathrm{K}}^{35}$.