This is an accepted version of a paper published in Nature. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the published paper: Hinke, C., Boehmer, M., Boutachkov, P., Faestermann, T., Geissel, H. et al. (2012) "Superallowed Gamow-Teller decay of the doubly magic nucleus 100 Sn" Nature, 486 (7403): [341][342][343][344][345] Access to the published version may require subscription.

Neutron-rich isotopes around lead, beyond N=126, have been studied exploiting the fragmentation of an uranium primary beam at the FRS-RISING setup at GSI. For the first time β-decay half-lives of 219 Bi and 211,212,213 Tl isotopes have been derived. The half-lives have been extracted using a numerical simulation developed for experiments in high-background conditions. Comparison with state of the art models used in r-process calculations is given, showing a systematic underestimation of the experimental values, at variance from close-lying nuclei.

The neutron-rich lead isotopes, up to 216 Pb, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond 208 Pb. The shell model is nowadays able to provide a comprehensive view of the atomic nucleus [1]. It is a many-body theoretical framework, successful in explaining various features of the structure of nuclei, based on the definition of a restricted valence space where a suitable Hamiltonian can be diagonalized. This effective interaction originates from realistic two-body nuclear forces based on phenomenological nucleon-nucleon potentials, renormalized to be adapted to the truncated model space. Although the renormalization process can be treated in a rigorous mathematical way, the appearance of effective terms is often neglected in calculations, as a common but incorrect practice. The presence and relevance of these effective forces is well known also in other fields of physics, as for example in condensed matter studies [2]. Indeed, effective three-body terms appear already at the lower perturbation order [3]: PRL 109, 162502 (2012) P H Y S I C A L

The low-lying structure of 188,190,192 W has been studied following β decays of the neutron-rich mother nuclei 188,190,192 Ta produced following the projectile fragmentation of a 1-GeV-per-nucleon 208 Pb primary beam on a natural beryllium target at the GSI Fragment Separator. The β-decay half-lives of 188 Ta, 190 Ta, and 192 Ta have been measured, with γ -ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion β-γ correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in 188 W, 190 W, and 192 W, which highlight a change in nuclear shape at 190 W compared with that of lighter W isotopes. This evolution of ground-state structure along the W isotopic chain is discussed as evidence for a possible proton subshell effect for the A ∼ 190 region and is consistent with maximization of the γ -softness of the nuclear potential around N ∼ 116.