Abstract
Lifetimes of excited states of the phosphorus isotopes have been measured by using the differential recoil-distance method. The isotopes of phosphorus were populated in binary grazing reactions initiated by a beam of ions of energy 225 MeV incident on a thin target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA -ray tracking array was used to detect rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were made within the range from about 1 to 100 ps. The number of states for which lifetime measurements were possible was limited by statistics. For , lifetime limits were determined for the first and states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first state of at 429 keV was determined and compared with earlier measurements. For , the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with values of , , , and , respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched state of at 5212 keV and a lifetime limit was established for the stretched state at 2030 keV. There are no previously published lifetimes for states of . Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF effective interaction. In addition, measured branching ratios, published mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. In general, there is good agreement between experiment and the shell model; however there is evidence that the shell-model values of the transition rates for the (ground state) and transitions in underestimate the experimental values by a factor between 5 and 10. In there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited states. In particular, there is a serious disagreement for the decay characteristics of the second state at 4493 keV, for which the shell-model counterpart lies at 4754 keV. In this case, the shell-model competing electromagnetic decay branches are dominated by and transitions.
22 More- Received 23 May 2019
- Revised 12 September 2019
DOI:https://doi.org/10.1103/PhysRevC.100.064308
©2019 American Physical Society