Resolution of a discrepancy in the γ-ray emission probability from the β decay of 137Ceg

We have deduced the emission probability of the 447-keV gamma ray from the epsilon + beta(+) decay of Ce-137(g) (9.0 h) relative to that of the 254-keV gamma ray from the Ce-137(m) (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 La-139(p, 3n) Ce-137(m,g) reaction by bombarding La-nat with a proton beam from the 88-in. cyclotron at Lawrence Berkeley National Laboratory. gamma-ray intensities were measured using an HPGe detector. The emission probability for the 447-keV gamma-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 gamma ray from the decay of Y-85(g) (2.68 h) relative to that of the 232-keV gamma ray from the Sr-85(m) (1.127 h) decay in transient equilibrium. The isotope was produced via the Sr-86(p, 2n) Y-85(g) reaction by bombarding (SrCO3)-Sr-86 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 gamma ray in the literature. Our work highlights the importance of explicit description by authors of any time-dependent correction they have made when reporting gamma-ray intensities for nuclides in transient equilibrium. The need and significance of accurate and precise decay data of Ce-137(g) and Y-85(g) in basic science and medicine is briefly outlined.