Lifetime of the , 1.013 MeV state and the excited-core model of 27Al

Abstract

Nuclear resonance fluorescence scattering was observed to measure the lifetime of the second excited state in 27Al at 1.013 MeV. The 27Al(p, p′γ)-reaction in a solid aluminium target served as a Doppler-broadened gamma source. The scattering experiment yielded a mean life of tm = 2.2±0.3 ps, corresponding to a magnetic dipole transition strength of (11.5±1.6)·10−3 Weisskopf units. The low-lying levels of 27Al are discussed in detail in terms of the excited-core model, taking a mixing of the two 32+ excited states into account. Agreement between the model predictions and the experimental data are obtained for a 15% quasi-particle admixture to the 32+ state at 1.013 MeV. To fit the energies of the multiplet states the core-hole interaction must contain multipoles of orders up to four.