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

TL;DR

This paper estimates the radiative lifetime and energy of the low-energy isomeric state in $^{229}$Th using phenomenological calculations based on experimental transition data, providing a favored range and proposing new measurements to refine these estimates.

Contribution

It offers a new estimation of the $^{229}$Th isomeric state's energy and lifetime, and highlights the importance of additional measurements to reduce current uncertainties.

Findings

Estimated the isomeric state's energy around 7.8 eV.

Predicted the transition lifetime with 90% confidence.

Identified key experimental parameters influencing current data.

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 $K^{\pi}[Nn_Z\Lambda]=5/2^+[633]$ 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.