Speaker
Description
The determination of $\beta$-feeding values from $\gamma$-ray spectroscopy data is a fundamental step in constructing reliable nuclear decay schemes and extracting log ft values. In the standard approach, absolute $\gamma$-ray intensities are determined and the population of each excited level is obtained from the intensity balance between $\gamma$ transitions feeding and depopulating that level. However, this procedure becomes inadequate in the presence of isomeric states with intermediate half-lives, for which the assumption of instantaneous decay or complete time separation is not valid. In such cases, $\gamma$-ray intensities observed in $\beta$–$\gamma$ and $\gamma$–$\gamma$ coincidence spectra can be significantly distorted, leading to underestimated transition strengths and, consequently, incorrect $\beta$-feeding values.
Analytical solutions can be derived for simple cases involving a single isomer or even straightforward sequential isomeric cascades. However, when multiple coupled isomeric states are arranged in a complex level scheme with numerous branching transitions, the time-dependent population and depopulation pathways become strongly interdependent. In such situations, analytical treatments become impractical, and a more flexible computational approach is required to extract consistent $\beta$-feeding values.
To address this issue, we have developed a dedicated code based on Monte Carlo simulations combined with a genetic algorithm optimization procedure. The program takes as input a proposed $\gamma$-ray decay scheme, known $\beta$-feeding intensities and level lifetimes (where available), as well as experimental information on time-dependent $\gamma$-ray intensities. Unknown $\beta$-feeding values and, where necessary, level lifetimes are initially sampled within predefined physical ranges. Through successive generations, the genetic algorithm converges toward a solution that reproduces the experimentally observed $\gamma$-ray intensities within their uncertainties. The final output provides a self-consistent set of $\beta$-feeding intensities and lifetimes compatible with the measured data.
The method has been tested on experimental data from the $\beta$ decay of Indium-124 to Tin-124. The level scheme of the daughter nucleus includes two low-lying isomeric states, which complicates the extraction of $\beta$ feeding for four excited levels. The evolutionary approach successfully resolved the feeding pattern and produced results consistent with independently determined level lifetimes.
The presented framework provides a robust and flexible tool for the analysis of complex decay schemes involving multiple isomeric states and can be readily applied to other cases encountered in high-precision $\gamma$-ray spectroscopy studies. By combining Monte Carlo simulations with a genetic optimization algorithm in a fully time-dependent treatment, the method offers a novel strategy for the simultaneous extraction of $\beta$-feeding intensities and level half-lives in systems with coupled isomers.
| Contribution category | Experiment |
|---|---|
| Presenter status | Student |