Low-lying resonance states in the Be-9 continuum

Excited states in Be-9 from 2 to 9 MeV are studied via beta delayed particle emission from Li-9. The broad overlapping particle unbound states are investigated using an extension of an experimental method developed for dealing with three-body decays of broad isolated levels. The results confirm the existence of a broad state at 5 MeV, with a width of 2 MeV. Angular correlations are used for firm spin determinations for this and other levels

Low-lying resonance states in the Be-9 continuum

Excited states in Be-9 from 2 to 9 MeV are studied via beta delayed particle emission from Li-9. The broad overlapping particle unbound states are investigated using an extension of an experimental method developed for dealing with three-body decays of broad isolated levels. The results confirm the existence of a broad state at 5 MeV, with a width of 2 MeV. Angular correlations are used for firm spin determinations for this and other levels

Branching ratios in the β decays of N12 and B12

Absolute branching ratios to unbound states in C12 populated in the β decays of N12 and B12 are reported. Clean sources of N12 and B12 were obtained using the isotope separation on-line (ISOL) method. The relative branching ratios to the different populated states were extracted using single-alpha as well as complete kinematics triple-alpha spectra. These two largely independent methods give consistent results. Absolute normalization is achieved via the precisely known absolute branching ratio to the bound 4.44 MeV state in C12. The extracted branching ratios to the unbound states are a factor of three more precise than previous measurements. Branching ratios in the decay of Na20 are also extracted and used to check the results. © 2009 The American Physical Society.Supported by the Academy of Finland (Project No. 44875), by the Spanish Agency CICYT (Nos. FPA2007–62170 and FPA2007–62216), by the European Union Sixth Framework Programme “EURONS” (No. 506065), by the Swedish Research Council, and the Knut and Alice Wallenberg foundation.Peer Reviewe

Neutron Halo Nuclei

In light nuclei close to the neutron drip-line a spatially extended neutron distribution, the neutron, halo occurs. This is due to the relatively small binding energy of the last neutrons which makes possible quantum mechanical tunnelling of the last neutron(s) far away from the nuclear core. There are two main paths in the experimental study of the structure of these nuclei: reactions with radioactive nuclear beams and beta-decays. <p> In reaction studies the momentum distributions from the fragments of reactions between halo nuclei and targets are studied. Results from measurements of (mainly) neutrons from the break-up of the two-neutron halo nucleus ¹¹Li and ¹¹Be with a single neutron halo are presented here. For ¹¹Li data from reactions at 29 MeV/B on three different targets Be, Ni and Au are shown. All the angular distributions of the neutrons are narrow. In reactions of 41 MeV/B ¹¹Be it is clearly seen that different reaction mechanisms are present for different charge of the target. For low Z targets nuclear dissociation reactions dominate yielding board neutron distributions. For targets with high proton number the main contributions is Coulomb dissociation, giving narrow angular distributions. <p> A systematic trend in the .beta.-decay of drip-line nuclei is very large beta-feeding to highly excited states in the daughter nuclei. When states above the separation energy of one or several nucleons are fed, beta-delayed particle emission will occur. Energy spectra of .beta.-delayed particles are analysed to yield information about nuclear structure. In this work is presented experimental data about beta-delayed charged particles, emitted in the decays of ^6,8He and ¹¹Li. In the decay of ⁶He .beta.-delayed deuteron emission was identified for the first time. For ⁸He and ¹¹Li new data concerning the triton branching ratios are presented. It is also shown that there could be a branch of. beta.-delayed deuterons present in the decay of ¹¹Li , which might be interpreted as the peripheral beta-decay of the two neutron halo

Neutron Halo Nuclei

In light nuclei close to the neutron drip-line a spatially extended neutron distribution, the neutron, halo occurs. This is due to the relatively small binding energy of the last neutrons which makes possible quantum mechanical tunnelling of the last neutron(s) far away from the nuclear core. There are two main paths in the experimental study of the structure of these nuclei: reactions with radioactive nuclear beams and beta-decays. In reaction studies the momentum distributions from the fragments of reactions between halo nuclei and targets are studied. Results from measurements of (mainly) neutrons from the break-up of the two-neutron halo nucleus 11Li and 11Be with a single neutron halo are presented here. For 11Li data from reactions at 29 MeV/B on three different targets Be, Ni and Au are shown. All the angular distributions of the neutrons are narrow. In reactions of 41 MeV/B 11Be it is clearly seen that different reaction mechanisms are present for different charge of the target. For low Z targets nuclear dissociation reactions dominate yielding board neutron distributions. For targets with high proton number the main contributions is Coulomb dissociation, giving narrow angular distributions. A systematic trend in the .beta.-decay of drip-line nuclei is very large beta-feeding to highly excited states in the daughter nuclei. When states above the separation energy of one or several nucleons are fed, beta-delayed particle emission will occur. Energy spectra of .beta.-delayed particles are analysed to yield information about nuclear structure. In this work is presented experimental data about beta-delayed charged particles, emitted in the decays of 6,8He and 11Li. In the decay of 6He .beta.-delayed deuteron emission was identified for the first time. For 8He and 11Li new data concerning the triton branching ratios are presented. It is also shown that there could be a branch of. beta.-delayed deuterons present in the decay of 11Li , which might be interpreted as the peripheral beta-decay of the two neutron halo

Study of Charged-Particles Emitted in the Beta-Decay of He-6,He-8

The beta-delayed charged particle spectra from He-6 and He-8 were measured with a telescope consisting of a gas counter and a Si surface barrier detector. Beta-delayed deuterons and tritons are emitted in the two cases with branching ratios of (7.6 +/- 0.6) x 10(-6), E(d) > 350 keV and (8.0 +/- 0.5) x 10(-3), respectively. Both spectra present anomalies that must be due to the special structure of these nuclei (an alpha core surrounded by several neutrons)

Super-Allowed Beta-Decay of Nuclei at the Drip-Line

We have investigated the continuous particle spectra following the beta decay of the neutron-rich nuclei that terminate the mass 6, 8, 9 and 11 isobaric chains. Strong beta transitions feeding the very top of the spectrum are found systematically. The favoured states are within a few MeV of the energy of the initial state. This phenomenon seems to be linked to the occurrence of a di-neutron structure or neutron halo in the drip-line nuclei