Investigation of the 3.46 MeV isomeric level of 38K with the 24Mg( 16O, pnγ) 38K reaction

Abstract

The τ 1 2 = 22 μs isomeric level of 38K at an excitation energy of 3458.0 ± 0.2keVf is strongly populated in the 24Mg( 16O, pnγ) 38K reaction. Delayed γ-rays are studied with Ge(Li), Si(Li), and NaI detectors. Accurate excitation energies, branching ratios and lifetimes of levels involved in the decay of the isomeric state are determined. The isomeric level predominantly decays by a dipole transition of 38.03±0.03 keV with a total conversion coefficient of α T = 0.42 ± 0.15. Mean lives of 38K levels are measured with the recoil-distance method. The results are τ m = 10.1 ± 0.9 ps, 1.41 ± 0.14 ns and 101 ± 15 ps for the levels at excitation energies of 0.46, 2.65 and 3.42 MeV, respectively. It is suggested that the (1f 7 2 ) 2 structure of a low-lying J π = 7 + state in combination with the selection rules for γ-decay in a self-conjugate nucleus is responsible for the isomerism.