UC Berkeley

We have deduced the emission probability of the 447-keV γ ray from the ϵ+β+ decay of Ceg137 (9.0 h) relative to that of the 254-keV γ ray from the Cem137 (34.4 h) decay in transient equilibrium. The time-dependent factor in transient equilibrium was applied following the Bateman equation for a radioactive decay chain. The isotope was produced via the La139(p,3n)Cem,g137 reaction by bombarding natLa with a proton beam from the 88-in. cyclotron at Lawrence Berkeley National Laboratory. γ-ray intensities were measured using an HPGe detector. The emission probability for the 447-keV γ ray deduced in this work is 1.21(3) (that is 1.21 ± 0.03) per hundred parent decays, which differs significantly from an earlier published value of 2.24(10). We identify the source of this discrepancy to be an incorrect use of the time-dependent factor. Additionally, we have deduced the emission probability of the 504-keV γ ray from the decay of Yg85 (2.68 h) relative to that of the 232-keV γ ray from the Srm85 (1.127 h) decay in transient equilibrium. The isotope was produced via the Sr86(p,2n)Yg85 reaction by bombarding SrCO386 with a proton beam at the same facility. The study confirms the assumption of the time-dependent correction for recommending the emission probability of the 504-keV γ ray in the literature. Our work highlights the importance of explicit description by authors of any time-dependent correction they have made when reporting γ-ray intensities for nuclides in transient equilibrium. The need and significance of accurate and precise decay data of Ceg137 and Yg85 in basic science and medicine is briefly outlined.