Decay of the 22-μs isomeric state of K38

The decay of the 22.5-μs isomer of K38 has been studied by observing the delayed γ rays following the Mg22(O16,pn)K38 and Cl35(α,n)K38 reactions. γ-ray singles and γ-γ coincidence measurements were made and the reaction threshold for production of the isomer was determined for the (α,n) reaction. The 3458-keV metastable state decays by an apparent E1 transition (αT=0.58) to a level at 3420 keV and by an 812-keV transition to a level at 2646 keV. The isomerism is understood in terms of the selection rules for the decay of E1 transitions in T=0 nuclei. A weak-coupling estimate of the excitation energy of the 7+(1f72)2 state in K38 yields a value in excellent agreement with that observed for this isomer. [RADIOACTIVITY K38 (3458-keV level) [from Mg24(O16,pn), Cl35(α,n)]; measured Eγ, Iγ, T12, γ-γ coin, (α,n) reaction threshold. Natural targets. Ge, Ge(Li), NaI(Tl) detectors.]