Spectroscopy of 26^{26}F

The structure of the weakly-bound $^{26}_{\;\;9}$F$_{17}$ odd-odd nucleus, produced from $^{27,28}$Na nuclei, has been investigated at GANIL by means of the in-beam $\gamma$-ray spectroscopy technique. A single $\gamma$-line is observed at 657(7) keV in $^{26}_{9}$F which has been ascribed to the decay of the excited J=$2^+$ state to the J=1$^+$ ground state. The possible presence of intruder negative parity states in $^{26}$F is also discussed.Comment: 3 pages, 1 figure, accepted for publication in Physical Review

Isomeric ratios in Hg-206

T. Alexander et al.; 5 págs.; 2 figs.; 1 tab.; PACS numbers: 25.70.Mn, 23.35.+g, 27.80.+w; Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 31–September 7, 2014.206Hg was populated in the fragmentation of an E∕A = 1 GeV 208Pb beam at GSI. It was part of a campaign to study nuclei around 208Pb via relativistic Coulomb excitation. The observation of the known isomeric states confirmed the identification of the fragmentation products. The isomeric decays were also used to prove that the correlations between beam identification detectors and the AGATA γ-ray tracking array worked properly and that the tracking efficiency was independent of the time relative to the prompt flash.Peer Reviewe

Collapse of the N=28 shell closure in 42^{42}Si

The energies of the excited states in very neutron-rich $^{42}$Si and $^{41,43}$P have been measured using in-beam $\gamma$-ray spectroscopy from the fragmentation of secondary beams of $^{42,44}$S at 39 A.MeV. The low 2$^+$ energy of $^{42}$Si, 770(19) keV, together with the level schemes of $^{41,43}$P provide evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that $^{42}$Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let

β decay of 129Cd and excited states in 129In

J. Taprogge et al.; 11 pags.; 8 figs.; 2 tabs.; PACS number(s): 23.20.Lv, 23.40.−s, 21.60.Cs, 27.60.+j©2015 American Physical Society. The β decay of 129Cd, produced in the relativistic fission of a 238U beam, was experimentally studied at the RIBF facility at the RIKEN Nishina Center. From the γ radiation emitted after the β decays, a level scheme of 129In was established comprising 31 excited states and 69 γ -ray transitions. The experimentally determined level energies are compared to state-of-the-art shell-model calculations. The half-lives of the two β-decaying states in 129Cd were deduced and the β feeding to excited states in 129In were analyzed. It is found that, as in most cases in the Z < 50, N 82 region, both decays are dominated by the ν0g7/2 → π0g9/2 Gamow–Teller transition, although the contribution of first-forbidden transitions cannot be neglected.This work was supported by the Spanish Ministerio de Ciencia e Innovacion under contracts FPA2009-13377-C02 and FPA2011-29854- C04, the Generalitat Valenciana (Spain) under grant PROMETEO/2010/101, the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. NRF-2012R1A1A1041763), the Priority Centers Research Program in Korea (2009-0093817), OTKA contract number K-100835, JSPS KAKENHI (Grant No. 25247045), the European Commission through the Marie Curie Actions call FP7-PEOPLE-2011-IEF under Contract No. 300096, the US Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357, the “RIKEN foreign research program,” and the German BMBF (No. 05P12RDCIA and 05P12RDNUP) and HIC for FAIR.Peer Reviewe

Octupole transitions in the 208Pb region

The 208Pb region is characterised by the existence of collective octupole states. Here we populated such states in 208Pb + 208Pb deep-inelastic reactions. γ-ray angular distribution measurements were used to infer the octupole character of several E3 transitions. The octupole character of the 2318 keV 17− → 14+ in 208Pb, 2485 keV 19/2 − → 13/2 + in 207Pb, 2419 keV 15/2 − → 9/2 + in 209Pb and 2465 keV 17/2 + → 11/2 − in 207Tl transitions was demonstrated for the first time. In addition, shell model calculations were performed using two different sets of two-body matrix elements. Their predictions were compared with emphasis on collective octupole states.This work is supported by the Science and Technology Facilities Council (STFC), UK, US Department of Energy, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357 and DE-FG02-94ER40834, NSF grant PHY-1404442

Coexistence of 'alpha+ 208Pb' cluster structures and single-particle excitations in 212Po

Excited states in 212Po have been populated by alpha transfer using the 208Pb(18O,14C) reaction at 85MeV beam energy and studied with the EUROBALL IV gamma multidetector array. The level scheme has been extended up to ~ 3.2 MeV excitation energy from the triple gamma coincidence data. Spin and parity values of most of the observed states have been assigned from the gamma angular distributions and gamma -gamma angular correlations. Several gamma lines with E(gamma) < 1 MeV have been found to be shifted by the Doppler effect, allowing for the measurements of the associated lifetimes by the DSAM method. The values, found in the range [0.1-0.6] ps, lead to very enhanced E1 transitions. All the emitting states, which have non-natural parity values, are discussed in terms of alpha-208Pb structure. They are in the same excitation-energy range as the states issued from shell-model configurations.Comment: 21 pages, 19 figures, corrected typos, revised arguments in Sect. III

β-Decay Half-Lives of 110 Neutron-Rich Nuclei across the N = 82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process

G. Larusso et al.; 7 pags.; 5 figs.; 2 tabs.; PACS numbers: 23.40.-s, 26.30.Hj, 27.60.+j© 2015 American Physical Society. The β-decay half-lives of 110 neutron-rich isotopes of the elements from 37Rb to 50Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A ≈ 130) and the rare-earth-element (A ≈ 160) abundance peaks may result from the freeze-out of an (n, γ) ⇄ (γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events.Part of the WAS3ABi was supported by the Rare Isotope Science Project which is funded by the Ministry of Education, Science, and Technology (MEST) and National Research Foundation (NRF) of Korea. This work was partially supported by KAKENHI (Grants No. 25247045, No. 2301752, and No. 25800130), the RIKEN Foreign Research Program, the Spanish Ministerio de Ciencia e Innovación (Contracts No. FPA2009-13377-C02 and No. FPA2011-29854-C04), the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, Contract No. DE-AC02-06CH11357, the NASA Grant No. NNX10AH78G, and the Hungarian Scientific Research Fund OTKA Contract No. K100835.Peer Reviewe