In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton ($2p$) emission from ${}^{67}\mathrm{Kr}$. At the same time, no evidence for $2p$ emission of ${}^{59}\mathrm{Ge}$ and ${}^{63}\mathrm{Se}$, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with $Q$ value predictions which pointed to ${}^{67}\mathrm{Kr}$ as being the best new candidate among the three for two-proton radioactivity. ${}^{67}\mathrm{Kr}$ is only the fourth $2p$ ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the $2p$ emission branching ratio is 37(14)%, and the half-life of ${}^{67}\mathrm{Kr}$ is 7.4(30) ms.

The low-lying structure of ${}^{188,190,192}\mathrm{W}$ has been studied following $\beta$ decays of the neutron-rich mother nuclei ${}^{188,190,192}\mathrm{Ta}$ produced following the projectile fragmentation of a 1-GeV-per-nucleon ${}^{208}\mathrm{Pb}$ primary beam on a natural beryllium target at the GSI Fragment Separator. The $\beta$-decay half-lives of ${}^{188}\mathrm{Ta}$, ${}^{190}\mathrm{Ta}$, and ${}^{192}\mathrm{Ta}$ have been measured, with $\gamma$-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion $\beta -\gamma$ correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in ${}^{188}\mathrm{W}$, ${}^{190}\mathrm{W}$, and ${}^{192}\mathrm{W}$, which highlight a change in nuclear shape at ${}^{190}\mathrm{W}$ 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 $\gamma$-softness of the nuclear potential around $N~116$.

L. Pellegri et al. ; 5 pags. ; 6 figs. ; open access article under the CC BY license. Funded by SCOAP3© 2014 The Authors. The γ decay from the high-lying states of 124Sn was measured using the inelastic scattering of 17O at 340 MeV. The emitted γ rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented δE-E silicon telescopes. The angular distribution was measured both for the γ rays and the scattered 17O ions. An accumulation of E1 strength below the particle threshold was found and compared with previous data obtained with (γ, γ') and (α, α'γ) reactions. The present results of elastic scattering, and excitation of E2 and E1 states were analysed using the DWBA approach. From this comprehensive description the isoscalar component of the 1- excited states was extracted. The obtained values are based on the comparison of the data with DWBA calculations including a form factor deduced using a microscopic transition density.Grant No. 2011/03/B/ST2/01894; (iii) the National Superconducting Cyclotron Laboratory at MSU; (iv) the US NSF Grant PHY-1204486; and the German BMBF under Grant 06KY9136.Peer Reviewe

This Letter reports on a systematic study of $\beta$-decay half-lives of neutron-rich nuclei around doubly magic ${}^{208}\mathrm{Pb}$. The lifetimes of the 126-neutron shell isotone ${}^{204}\mathrm{Pt}$ and the neighboring ${}^{200–202}\mathrm{Ir}$, ${}^{203}\mathrm{Pt}$, ${}^{204}\mathrm{Au}$ are presented together with other 19 half-lives measured during the “stopped beam” campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of $r$-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden $\beta$ strength reveal significant deviations for most of the nuclei with $N<126$. In contrast, theories including a fully microscopic treatment of allowed and first-forbidden transitions reproduce more satisfactorily the trend in the measured half-lives for the nuclei in this region, where the r-process pathway passes through during $\beta$ decay back to stability.

The neutron-rich lead isotopes, up to ${}^{216}\mathrm{Pb}$, 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 ${}^{208}\mathrm{Pb}$.

The properties of pygmy dipole states in ${}^{208}\mathrm{Pb}$ were investigated using the ${}^{208}\mathrm{Pb}$(${}^{17}\mathrm{O}$, ${}^{17}\mathrm{O}’\gamma$) reaction at 340 MeV and measuring the $\gamma$ decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted $\gamma$ rays and of the scattered particles were measured. The results are compared with ($\gamma$, ${\gamma }^{\prime }$) and ($p$, $p^{\prime }$) data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the $2^{+}$ and $3^{-}$ states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first time. This has allowed us to extract the isoscalar component of the $1^{-}$ excited states from 4 to 8 MeV.