$^{133}$In: A Rosetta Stone for decays of r-process nuclei

The <math display="inline"><mi>β</mi></math> decays from both the ground state and a long-lived isomer of <math display="inline"><mrow><mmultiscripts><mrow><mi>In</mi></mrow><mprescripts/><none/><mrow><mn>133</mn></mrow></mmultiscripts></mrow></math> were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to <math display="inline"><mi>β</mi></math>, <math display="inline"><mi>γ</mi></math>, and neutron spectroscopy, the comparative partial half-lives (<math display="inline"><mi>log</mi><mi>f</mi><mi>t</mi></math>) have been measured for all their dominant <math display="inline"><mi>β</mi></math>-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their <math display="inline"><mi>β</mi></math> decays selectively populate only a few isolated neutron unbound states in <math display="inline"><mrow><mmultiscripts><mrow><mi>Sn</mi></mrow><mprescripts/><none/><mrow><mn>133</mn></mrow></mmultiscripts></mrow></math>. Precise energy and branching-ratio measurements of those resonances allow us to benchmark <math display="inline"><mi>β</mi></math>-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the <math display="inline"><mi>β</mi></math> decay of neutron-rich nuclei southeast of <math display="inline"><mrow><mmultiscripts><mrow><mi>Sn</mi></mrow><mprescripts/><none/><mrow><mn>132</mn></mrow></mmultiscripts></mrow></math> and will serve as a guide for future theoretical development aiming to describe accurately the key <math display="inline"><mi>β</mi></math> decays in the rapid-neutron capture (<math display="inline"><mi>r</mi></math>-) process.