Lifetime measurements of N similar or equal to 20 phosphorus isotopes using the AGATA gamma-ray tracking spectrometer

Lifetimes of excited states of the phosphorus isotopes P-33, 34, 35, 36(15) 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 S-36 ions of energy 225 MeV incident on a thin Pb-208 target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA gamma-ray tracking array was used to detect gamma-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 P-33, lifetime limits were determined for the first 3/2(+) and 5/2(+) states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first 2(+) state of P-34 at 429 keV was determined and compared with earlier measurements. For P-35, the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with J(pi) values of 3/2(+), 5/2(+), 7/2(1)(-) and 7/2(2)(-), respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched pi(1f(7/2)) circle times nu(1f(7/2)) J(pi )= (7(+)) state of P-36 at 5212 keV and a lifetime limit was established for the stretched pi(1d(3/2)) circle times nu(1f(7/2)) J(pi )= (5(-)) state at 2030 keV. There are no previously published lifetimes for states of P-36. 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 M1 transition rates for the 3/2(1)(+)-> 1/2(+) (ground state) and 5/2(1)(+) -> 3/2(1)(+) transitions in P-33 underestimate the experimental values by a factor between 5 and 10. In P-35 there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited 7/2(-) states. In particular, there is a serious disagreement for the decay characteristics of the second 7/2(-) 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 E1 and M1 transitions.