Three-centre cluster structure in 11C and 11B

Studies of the 16O(9Be,alpha 7Be)14C, 7Li(9Be,alpha 7Li)5He and 7Li(9Be,alpha alpha t)5He reactions at E(beam)=70 and 55 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into alpha+7Be(gs) are observed between 8.5 and 13.5 MeV. The alpha+7Li(gs), alpha+7Li*(4.652 MeV) and t+8Be(gs) decays of 11B excited states between 9 and 19 MeV are observed. The decay processes are used to indicate the possible three-centre 2alpha+3He (2alpha+3H) cluster structure of observed states. This cluster structure is more prominent in the positive-parity states, where two rotational bands with large deformations are suggested. Excitations of some of the observed T=1/2 resonances coincide with the energies of previously measured T=3/2 isobaric analogs of the 11Be states,indicating that these states may have mixed isospin.Comment: Contribution for the proceedings of the NUSTAR'05: NUclear STructure, Astrophysics and Reactions, University of Surrey, Guildford, UK; accepted for publication in Journal of Physics

A review of the freshwater diversity in the Okavango Delta and Lake Ngami (Botswana): taxonomic composition, ecology, comparison with similar systems and conservation status

Freshwater organisms in the Okavango Delta and Lake Ngami (Botswana) provide direct and indirect benefits to people and the economy of the region. However, their existence could be potentially threatened by human activities (primarily, upstream water abstraction and planned hydropower structures) coupled with climate change. For their protection, it is essential to know their distribution, ecology, and status of the ecosystems that they inhabit. Publications that record taxa from the Delta at species level are scarce, particularly aquatic macroinvertebrates. Identifying organisms to species level can provide more accurate information for environmental monitoring and conservation programmes but requires significant training and expertise. Here, we present a comprehensive taxonomical review of 2204 freshwater species from the Okavango Delta and Lake Ngami, with additional 355 species found in other areas of Botswana that are likely to be present in the study region. We also compare the diversity of the Okavango Delta and Lake Ngami with two other tropical wetlands: the Pantanal (Brazil) and the Kakadu Region (Australia). We show that biodiversity in the Okavango Delta and Lake Ngami is higher than in previous estimates, with recorded species richness dominated by phytoplankton and macroinvertebrates. Most species are widespread across the system and southern Africa. The resulting database includes new records (Bryozoa, Porifera), information on species conservation status, habitat, ecology, distribution in continental Africa, site details and taxonomical notes. This will be an essential resource for researchers, conservation managers, policy makers and consultants investigating freshwater biodiversity in tropical wetlands in the region

Binary reaction decays from 24Mg+12C

Charged particle and gamma decays in 24Mg* are investigated for excitation energies where quasimolecular resonances appear in 12C+12C collisions. Various theoretical predictions for the occurence of superdeformed and hyperdeformed bands associated with resonance structures with low spin are discussed within the measured 24Mg* excitation energy region. The inverse kinematics reaction 24Mg+12C is studied at E_lab(24Mg) = 130 MeV, an energy which enables the population of 24Mg states decaying into 12C+12C resonant break-up states. Exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON Tandem facility at Strasbourg. Specific structures with large deformation were selectively populated in binary reactions and their associated gamma decays studied. Coincident events associated with inelastic and alpha-transfer channels have been selected by choosing the excitation energy or the entry point via the two-body Q-values. The analysis of the binary reaction channels is presented with a particular emphasis on 24Mg-gamma, 20Ne-gamma and 16O-gamma coincidences. New information (spin and branching ratios) is deduced on high-energy states in 24Mg and 16O, respectively.Comment: 27 pages, 8 figures, 1 tabl

4He decay of excited states in 14C

A study of the 7Li(9Be,4He 10Be)2H reaction at E{beam}=70 MeV has been performed using resonant particle spectroscopy techniques and provides the first measurements of alpha-decaying states in 14C. Excited states are observed at 14.7, 15.5, 16.4, 18.5, 19.8, 20.6, 21.4, 22.4 and 24.0 MeV. The experimental technique was able to resolve decays to the various particle bound states in 10Be, and provides evidence for the preferential decay of the high energy excited states into states in 10Be at ~6 MeV. The decay processes are used to indicate the possible cluster structure of the 14C excited states.Comment: accepted for publication in PR

Emergence of the N=16 shell gap in 21O

The spectroscopy of O21 has been investigated using a radioactive O20 beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jπ=5/2+ and 1/2+, respectively. Two neutron unbound states were observed at excitation energies of 4.77(10) and 6.17(11) MeV. The spectroscopic factor deduced for the lower of these, interpreted as a 3/2+ level, reveals a relatively pure (60%) 0d3/2 single-particle configuration, in good agreement with shell-model calculations that predict O26 to be unbound. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 shell gap, which is estimated to be 5.1(11) MeV. For the higher-lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 0.71(22) branching ratio to the first 2+ state in O20 has been observed.Unión Europea EURISOL 515768 RIDSNSF PHY-075809

Reaction mechanisms in 24Mg+12C and 32S+24Mg

The occurence of "exotic" shapes in light N=Z alpha-like nuclei is investigated for 24Mg+12C and 32S+24Mg. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures with low spin are presented. For both reactions, exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON Tandem facility of Strasbourg. Specific structures with large deformation were selectively populated in binary reactions and their associated $\gamma$-decays studied. The analysis of the binary and ternary reaction channels is discussed.Comment: 7 pages, 4 figures, Paper presented at the Fusion08 International Conference on New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, Chicago. Proceedings to be published by AIP Conference Proceedings Illinois, USA, September 22-26, 200

Structure of 12Be: intruder d-wave strength at N=8

The breaking of the N=8 shell-model magic number in the 12Be ground state has been determined to include significant occupancy of the intruder d-wave orbital. This is in marked contrast with all other N=8 isotones, both more and less exotic than 12Be. The occupancies of the 0 hbar omega neutron p1/2-orbital and the 1 hbar omega, neutron d5/2 intruder orbital were deduced from a measurement of neutron removal from a high-energy 12Be beam leading to bound and unbound states in 11Be.Comment: 5 pages, 2 figure

Clusters in Light Nuclei

A great deal of research work has been undertaken in the alpha-clustering study since the pioneering discovery, half a century ago, of 12C+12C molecular resonances. Our knowledge of the field of the physics of nuclear molecules has increased considerably and nuclear clustering remains one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. In this work, the occurence of "exotic" shapes in light N=Z alpha-like nuclei is investigated. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures are presented. Results on clustering aspects are also discussed for light neutron-rich Oxygen isotopes.Comment: 12 pages, 5 figures. Invited Talk presented by C. Beck at the Zakopane Conference on Nuclear Physics "Extremes of the Nuclear Landscape" XLV in the series of Zakopane Schools of Physics - International Symposium - Zakopane, Poland, August 30 - September 5, 2010.To be publihed in Acta Physica Polonica B42 no 3, March 201