Lifetime measurements in ²⁷Al

Abstract

The Doppler-shift attenuation method has been used to obtain lifetime estimates of 27Al levels up to 4.6 MeV. Gamma rays following inelastic scattering of protons at Ep = 4.5 and 6.0 MeV were detected in a 40-cm3 Ge(Li) detector surrounded by a shielded split annulus NaI(Tl) detector. The mean lives of the indicated states were determined as: 1014 keV, 1.5 ± 0.4 ps; 2211 keV, 55 ± 9 fs; 2734 keV. 16 ± 7 fs; 2980 keV, 14 ± 6 fs; 3003 keV, 83 ± 7 fs; 3678 keV, < 30 fs; 3955 keV. < 20 fs; 4054 keV, < 20 fs; 4408 keV, < 22 fs; 4509 keV, 300 ± 30 fs; 4580 keV, < 30 fs. Branching ratios for these states are reported. The lifetime and decay mode of the 4509-keV level, which decays to the 7/2+ 2211-keV state and the 9/2+ 3003-keV state, indicate that this state is possibly the 11/2+ member of the ground-state rotational band. The lifetime of the 3003-keV state is inconsistent with a recent assignment of spin-parity 7/2+ to this level.