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Half-lives of the low-lying yrast states of $^{212}$Po have been measured using the delayed coincidence fast-timing method. We report on the first measurement of the 41+ half-life, as well as a new measurement of the 61+ half-life with improved accuracy compared to previous studies. The extracted lifetime of the 41+ and 61+ state have been determined to be 100(14) ps and 1.66(28) ns respectively. With these measurements, precise values are now available for the reduced transition strengths B(E2) of all ground state band levels in $^{212}$Po up to the first 8+ state, in particular B(E2; 41+→21+) = 9.4(13) W.u. and B(E2;61+→41+) = 8.7(15) W.u. Comparison of the new available data with an α-clustering model calculation provides evidence that the inclusion of the α-cluster degree of freedom significantly improves agreement with experimental data compared to earlier shell model calculations.

International audience; The structure of $^{80}$Ge has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying $0^+_2$ intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV $γ$ ray, and suggested it as evidence for shape coexistence in $^{80}$Ge. We used the $\beta$ decay from the $3^-$ 22.4-keV state in $^{80}$Ga to enhance the population of low-spin states in $^{80}$Ge, including any excited $0^+$ level, and $\gamma \gamma$ coincidences to investigate it. We observed a 1764-keV $\gamma$ ray in coincidence with strong transitions in $^{80}$Ge, thus not feeding the proposed 639-keV $0^+_2$. No connecting transitions from previously known levels to the 639-keV and 2403-keV $2^+_3$ states could be established either. Shell-model calculations for Ge isotopes and $N=48$ isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a $0^+_2$ state below $≈1200$ keV in $^{80}$Ge. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying $0^+_2$ state in $^{80}$Ge.

12 pags., 8 figs., 1 tab., The structure of Ge80 has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying 02+ intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV γ ray, and suggested it as evidence for shape coexistence in Ge80. We used the β decay from the 3- 22.4-keV state in Ga80 to enhance the population of low-spin states in Ge80, including any excited 0+ level, and γγ coincidences to investigate it. We observed a 1764-keV γ ray in coincidence with strong transitions in Ge80, thus not feeding the proposed 639-keV 02+. No connecting transitions from previously known levels to the 639-keV and 2403-keV 23+ states could be established either. Shell-model calculations for Ge isotopes and N=48 isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a 02+ state below ≈1200 keV in Ge80. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying 02+ state in Ge80., This work was supported by Spanish national projects FPA2015-65035-P, RTI2018-098868-B-I00, and PID2019- 104390GB-I00, by Grupo de Física Nuclear (GFN) at Universidad Complutense (Spain), by the U.S. DoE Grant No. DE-FG02-94ER40834, and by the German BMBF Grant 05P19PKFNA. The support by the European Union Seventh Framework through ENSAR (Contract No. 262010) and by the ISOLDE Collaboration and technical teams is acknowledged.

The elastic scattering of the weakly bound radioactive nuclei B8 and Be7 from a Pb208 target was measured for the first time in the energy range around the Coulomb barrier. The data were analyzed using the optical model and the continuum discretized coupled channels (CDCC) formalisms. The reaction cross sections extracted from the optical model fits clearly indicate a remarkably enhanced reaction probability for the very weakly bound B8 (Sp=137.5keV) compared to similar mass nuclei interacting with the same target nucleus. CDCC calculations assuming a He3+He4 cluster model well described the Be7 experimental elastic scattering angular distributions, whereas the use of a Be7+p cluster model of B8 with an inert Be7 core gave a relatively poor description of the corresponding experimental data, suggesting that this model may be too simplistic and the possibility of core excitation should not be ignored.

18 pags., 10 figs., 4 tabs., The β- decay of Zn81 to the neutron magic N=50 nucleus Ga81, with only three valence protons with respect to Ni78, was investigated. The study was performed at the ISOLDE facility at CERN by means of γ spectroscopy. The Zn81 half-life was determined to be T1/2=290(4) ms while the β-delayed neutron emission probability was measured as Pn=23(4)%. The analysis of the β-gated γ-ray singles and γ-γ coincidences from the decay of Zn81 provides 47 new levels and 70 new transitions in Ga81. The β-n decay of Zn81 was observed and a new decay scheme into the odd-odd Ga80 nucleus was established. The half-lives of the first and second excited states of Ga81 were measured via the fast-timing method using LaBr3(Ce) detectors. The level scheme and transition rates are compared to large-scale shell-model calculations. The low-lying structure of Ga81 is interpreted in terms of the coupling of the three valence protons outside the doubly magic Ni78 core., This work was supported by the Spanish MINECO through the FPA2015-65035-P and RTI2018-098868-B-I00 projects, by the U.S. DoE Grant No. DE-FG02-94ER40834, by the German BMBF Grant 05P19PKFNA, and Grupo de Física Nuclear (GFN) at UCM. The support by the European Union Seventh Framework through ENSAR (Contract No. 262010) and ISOLDE (CERN) Collaboration is acknowledged. V.P. acknowledges support by the Spanish FPI-BES-2011-045931 grant.

The elastic scattering process for the nuclear reactions induced by the Radioactive Ion Beams Be-7 and B-8 on a Pb-208 target was measured for the first time in the energy range around the Coulomb barrier. Extensive theoretical calculations within the framework of the optical model were performed. An excellent agreement between experimental data and theoretical predictions was achieved for the reaction Be-7 + Pb-208 while a comprehensive understanding of the reaction dynamics induced by the more exotic projectile B-8 is still far to be reached. Predictions of the cross section for the breakup for both systems will also be given.

The elastic scattering of the weakly bound radioactive nuclei B8 and Be7 from a Pb208 target was measured for the first time in the energy range around the Coulomb barrier. The data were analyzed using the optical model and the continuum discretized coupled channels (CDCC) formalisms. The reaction cross sections extracted from the optical model fits clearly indicate a remarkably enhanced reaction probability for the very weakly bound B8 (Sp=137.5keV) compared to similar mass nuclei interacting with the same target nucleus. CDCC calculations assuming a He3+He4 cluster model well described the Be7 experimental elastic scattering angular distributions, whereas the use of a Be7+p cluster model of B8 with an inert Be7 core gave a relatively poor description of the corresponding experimental data, suggesting that this model may be too simplistic and the possibility of core excitation should not be ignored. © 2019 American Physical Society. UK.

The structure of 80Ge has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying 0+2 intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV γ ray, and suggested it as evidence for shape coexistence in 80Ge. We used the β decay from the 3− 22.4-keV state in 80Ga to enhance the population of low-spin states in 80Ge, including any excited 0+ level, and γγ coincidences to investigate it. We observed a 1764-keV γ ray in coincidence with strong transitions in 80Ge, thus not feeding the proposed 639-keV 0+2. No connecting transitions from previously known levels to the 639-keV and 2403-keV 2+3 states could be established either. Shell-model calculations for Ge isotopes and N=48 isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a 0+2 state below ≈1200 keV in 80Ge. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying 0+2 state in 80Ge.

We investigated the reaction dynamics induced by the Be-7, B-8+Pb-208 collisions at energies around the Coulomb barrier. Charged particles originated by both the collisions were detected by means of 6 Delta E-E-res telescopes of a newly developed detector array. Experimental data were analysed within the framework of the Optical Model and the total reaction cross-sections were compared together and with the Li-6,Li-7+Pb-208 collision data. According to the preliminary results, Be-7 nucleus reactivity is rather similar to the Li-7 one whereas the B-8+Pb-208 total reaction cross section appears to be much larger than those measured for reactions induced by the other weakly-bound projectiles on the same target.

this contribution we describe the first results obtained for the investigation of the elastic scattering process in the reactions induced by the Radioactive Ion Beams Be-7 and B-8 on a Pb-208 target at Coulomb barrier energies. The experimental data were analyzed within the framework of the optical model in order to extract the total reaction cross section. The comparison with data available in literature for reactions induced on Pb-208 by light ions in the mass range A = 6-8 shows that the loosely-bound( 8)B has the largest reactivity.