Long-lived non-equilibrium population of Fe3+ electronic states after the K-capture of 57Co

Abstract Mossbauer emission spectra of a frozen aqueous solution of 57 CoCl 2 show contributions from the S z = + 5 2 and the S z = + 3 2 Zeeman levels of Fe 3+ ions at T = 4.2 K in H ⪆ 30 kG. The K-capture results in a non-equilibrium state of relaxation time comparable to the lifetime of the nuclear excited state (∼ 10 −7 s).