Elucidating the nature of the proton radioactivity and branching ratio on the first proton emitter discovered 53mCo

The observation of a weak proton-emission branch in the decay of the 3174keV Co-53m isomeric state marked the discovery of proton radioactivity in atomic nuclei in 1970. Here we show, based on the partial half-lives and the decay energies of the possible proton-emission branches, that the exceptionally high angular momentum barriers, l(p) = 9 and l(p) = 7, play a key role in hindering the proton radioactivity from Co-53m, making them very challenging to observe and calculate. Indeed, experiments had to wait decades for significant advances in accelerator facilities and multi-faceted state-of-the-art decay stations to gain full access to all observables. Combining data taken with the TASISpec decay station at the Accelerator Laboratory of the University of Jyv & auml;skyl & auml;, Finland, and the ACTAR TPC device on LISE3 at GANIL, France, we measured their branching ratios as b(p1) = 1.3(1)% and b(p2) = 0.025(4)%. These results were compared to cutting-edge shell-model and barrier penetration calculations. This description reproduces the order of magnitude of the branching ratios and partial half-lives, despite their very small spectroscopic factors.

Automated summary

This article discusses the discovery of proton radioactivity in atomic nuclei in 1970. The authors show that high angular momentum barriers play a key role in hindering the observation and calculation of proton radioactivity in Co-53m. Despite the challenges faced in studying this phenomenon, significant advances have been made through the use of cutting-edge equipment and research methods.