The alpha decay of U-233 is a well-established approach to obtain Th-229 atoms or ions in the isomeric state. In fact, it is the only method to date that has been shown to be capable of populating the isomer. Still, the probability of feeding the isomer has not been measured. A value of 2% is often found in literature, yet retracing how this number was obtained is difficult.

We used the available U-233 decay data from the NuDat database and, based on this data, calculated a probability of at least 1.98% for the isomer population. The NuDat data was generated by estimating or assuming a set of branching ratios for gamma and internal conversion transitions. The NuDat database can therefore be used as a reference for the 2%-value, but this value is based on estimated (not measured) branching ratios.

A short essay on the topic can be found here, questions and comments to the author are more than welcome!