Mw Greene

Lifetimes and decays of energy levels in 30Si and 30P

Abstract The mean lifetimes of 15 levels in 30 Si and of 7 levels in 30 P have been measured by the Doppler-shift attenuation method. Limits on the lifetimes of a further 8 levels in 30 Si and of the 3018 keV level in 30 P have been obtained. Branching ratios and excitation energies have been measured in both nuclei. The levels were populated by the reactions 27 Al(α, p) 30 Si and 27 Al(α, n) 30 P at α-particle bombarding energies of 5.0, 6.3 and 8.0 MeV. Theγ-rays were detected with a Ge(Li)-NaI(Tl) escape suppressed and pair escape spectrometer.

Lifetimes and decay modes of energy levels in 34S

Abstract The excitation energies, branching ratios, and mean lifetimes of the low-lying levels in 34 S were measured. The lifetimes were measured by the Doppler shift attenuation method using the 31 P(α, p) 34 S reaction at a bombarding energy of 7.0 MeV. The γ-rays were detected at six angles with a Ge(Li)-NaI(Tl) anti-Compton and pair spectrometer. The mean lifetimes, in fs, were found to be: 2127 keV, 440 ± 50; 3303 keV, 218±30; 3915 keV, 1600±130; 4075 keV,

Lifetime measurements in 40K

The Doppler-shift attenuation method has been used to measure the lifetimes of 19 levels in 40K and four levels in 40Ar. Limits have also been set on the lifetimes of other levels in 40K. The measurements were made using the 37Cl(α, n)40K and 37Cl(α, p)40Ar reactions. Enriched targets of lead chloride and barium chloride were used. The lifetimes obtained with different stopping materials and different recoil velocities were compared where possible and were found to be consistent. A γγ coincidence experiment was performed to elucidate the decay schemes in 40K and 40Ar. The negative-parity states of 40K have γ-ray decay schemes consistent with simple shell-model calculations for d32−1f72 and d32−1p32 configurations. More information is needed before the 2p-2h and 4p-4h positive-parity states can be classified.

Lifetime measurements of levels of 38Ar

Abstract Lifetimes have been measured for 11 levels of 38 Ar using the Doppler-shift attenuation method with the 35 Cl(α, p) 38 Ar reaction. Limits on the lifetimes of four other levels have also been obtained. Several previously unknown γ-ray decay branching ratios have been measured. The other measured branching ratios agree with earlier data except for the decay of the level at 5513 keV. Assignments of 2 + for the 5156 keV level and 3 − for the 5513 keV level are confirmed. The agreement of the lifetimes of the negative parity states with previous shell-model calculations is unsatisfactory for J π = 3 − levels.

Decay and lifetimes of levels in 21Ne

Levels in 21Ne have been studied using the reaction 18O( alpha ,n) 21Ne. Lifetimes have been obtained for the states at 350, 1745, 2866, 3662, 4432, 5772 and 6548 keV by the Doppler shift attenuation method. The lifetimes are generally a factor of two to four smaller than previous measurements. The major part of these differences may be accounted for by discrepancies between the Warburton and Blaugrund approaches to the stopping theory when heavy stoppers are used. The lifetimes are compared with Nilsson model calculations and with predictions of the projected Hartree-Fock model.

A study of the principal decay modes and lifetimes of levels in 29Si below 7.2 MeV

The principal decay modes and lifetimes of levels populated in the reaction 26Mg( alpha ,n)29Si have been studied. Lifetimes were measured by the Doppler shift attenuation method at beam energies of 5.0, 6.75, 8.0 and 9.25 MeV. There is good agreement with previous results and two new lifetimes of 20+or-8 fs for the 5813 keV level and 47+or-14 fs for the 7016 keV level have been measured. Thirteen new lifetime limits have also been obtained. The lifetime limit of the 5653 keV level restricts its spin to 9/2+. This level, and that at 7139 keV, are proposed as the 9/2+ and 11/2+ members of the Kpi =3/2+ rotational band and evidence is presented for the inclusion of the 6781 keV level in the Kpi =7/2+ band.