Radiative lifetime and energy of the low-energy isomeric level in ${}^{229}$Th

Abstract

We estimate the range of the radiative lifetime and energy of the anomalous, low-energy $3/2^{+}(7.8\pm 0.5$ eV) state in the ${}^{229}$Th nucleus. Our phenomenological calculations are based on the available experimental data for the intensities of $M1$ and $E2$ transitions between excited levels of the ${}^{229}$Th nucleus in the $K^{\pi }[N{n}_Z\Lambda ]=5/2^{+}[633]$ and $3/2^{+}[631]$ rotational bands. We also discuss the influence of certain branching coefficients, which affect the currently accepted measured energy of the isomeric state. From this work, we establish a favored region where the transition lifetime and energy should lie at roughly the 90% confidence level. We also suggest new nuclear physics measurements, which would significantly reduce the ambiguity in the present data.

Comments: 12 pages, 5 figures