Lifetime measurements of states of S 35 , S 36 , S 37 , and S 38 using the AGATA γ -ray tracking spectrometer

Le résumé fourni par la source

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers $A=35$, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of $^{36}\mathrm{S}$ ions of energy 225 MeV incident on a thin $^{208}\mathrm{Pb}$ target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA $\ensuremath{\gamma}$-ray tracking array was used to detect $\ensuremath{\gamma}$ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For $^{35}\mathrm{S}$, the lifetime was determined for the first $1/{2}^{+}$ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the ${3}^{\ensuremath{-}}$ state of $^{36}\mathrm{S}$ at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (${6}^{+}$) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For $^{37}\mathrm{S}$, the states for which lifetime limits were established were those at 646 keV with ${J}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}}$ and at 2776 keV with ${J}^{\ensuremath{\pi}}=11/{2}^{\ensuremath{-}}$; there are no previously published lifetime values for excited states of $^{37}\mathrm{S}$. Finally, a lifetime limit was established for the ${J}^{\ensuremath{\pi}}=({6}^{+})$ state of $^{38}\mathrm{S}$ at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

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