LIFETIMES ENERGIES AND BRANCHING RATIOS OF 28SI EXCITED STATES

The γ decay of Si28 energy levels excited in the Al27(p,γ)Si28 reaction has been investigated with a 20-cm3 Ge(Li) detector. Energies of levels below 7 MeV have been measured to an accuracy of <1 keV by comparison with the Co56 spectrum. The 6878-keV 3- and 6889-keV 4+ doublet is found to be split by 10.9±0.5 keV; decay of the 6878-keV state to the 4617-keV level has been definitely established. Several branching ratios have been measured for the first time, or with improved accuracy. Mean lifetimes of excited states have been derived from observed γ-ray Doppler shifts, with the following results: 4617 keV (0.061±0.004 psec), 7380 keV (0.013±0.003 psec), 7416 keV (0.040±0.003 psec), 8260 keV (0.014±0.006 psec), 8588 keV (0.025±0.005 psec), 9163 keV (0.039±0.005 psec), 9316 keV (<0.01 psec), and 10 213 keV (0.015±0.007 psec); previously published lifetimes have been confirmed for levels at 1779, 6276, 6878, 7798, and 8413 keV. A probable spin-parity assignment of 2+ is made for the 9163-keV state. The small E2 transition strengths from the level at 7416 keV to the ground and first excited states are consistent with Hartree-Fock predictions that this is the 2+ member of a rotational band whose ground state is the 6.68 (0+) level. © 1968 The American Physical Society.