Resolution of a discrepancy in the γ -ray emission probability from the β decay of Ceg137

Abstract

We have deduced the emission probability of the 447-keV $\ensuremath{\gamma}$ ray from the $\ensuremath{\varepsilon}+{\ensuremath{\beta}}^{+}$ decay of $^{137}\mathrm{Ce}^{g}$ (9.0 h) relative to that of the 254-keV $\ensuremath{\gamma}$ ray from the $^{137}\mathrm{Ce}^{m}$ (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 $^{139}\mathrm{La}(p,3n)^{137}\mathrm{Ce}^{m,g}$ reaction by bombarding ${}^{\mathrm{nat}}\mathrm{La}$ with a proton beam from the 88-in. cyclotron at Lawrence Berkeley National Laboratory. $\ensuremath{\gamma}$-ray intensities were measured using an HPGe detector. The emission probability for the 447-keV $\ensuremath{\gamma}$ ray deduced in this work is 1.21(3) (that is 1.21 \ifmmode\pm\else\textpm\fi{} 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 $\ensuremath{\gamma}$ ray from the decay of $^{85}\mathrm{Y}^{g}$ (2.68 h) relative to that of the 232-keV $\ensuremath{\gamma}$ ray from the $^{85}\mathrm{Sr}^{m}$ (1.127 h) decay in transient equilibrium. The isotope was produced via the $^{86}\mathrm{Sr}(p,2n)^{85}\mathrm{Y}^{g}$ reaction by bombarding $^{86}\mathrm{SrCO}_{3}$ 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 $\ensuremath{\gamma}$ ray in the literature. Our work highlights the importance of explicit description by authors of any time-dependent correction they have made when reporting $\ensuremath{\gamma}$-ray intensities for nuclides in transient equilibrium. The need and significance of accurate and precise decay data of $^{137}\mathrm{Ce}^{g}$ and $^{85}\mathrm{Y}^{g}$ in basic science and medicine is briefly outlined.