M. Zadro

8Li + α decay of 12B and its possible astrophysical implications

The 12B excitation energy spectrum has been obtained from coincidence measurements of the 9Be + 7Li → 2α + 8Li reaction at E0 = 52 MeV. The decay of the states at excitations between 10 and 16 Mev into α + 8Li has been observed for the first time. Observed α-decay indicates possible cluster structure of the 12B excited states. The influence of these states on the cross-section of the astrophysically important 8Li(α,n)11B and 9Be + t reactions is discussed and the results are compared with existing results.

α-5He decaying states and the ground-state rotational band of 9Be

In a measurement of the 9Be(7Li, 7Liα)αn reaction at Ei = 52 MeV it is unambigously established for the first time that the 9Be excited states around 6.5 and 11.3 MeV decay into the α + 5He channel. This fact may support previous claims that the 11.3 MeV state is also a member of the ground-state rotational band.

Transfer, sequential decay, and quasi-free reactions induced by 18-MeV 6He beam on 6Li, 7Li, and 12C

The 6He + 6,7Li and 6He + 12C scattering and reactions have been studied using an 18-MeV 6He beam. Experimental results for the elastic scattering on all three targets are in fair agreement with optical model predictions, using the potentials found in the analysis of the 6Li scattering on the same targets and at close beam energies. Several two-body exit channels show clear signatures of a direct reaction mechanism allowing extraction of spectroscopic information. The measured angular distribution for the 6He + 6Li → α + 8Li reaction indicated close similarity between the α + 2n configuration in 6He and the α + d configuration in 6Li. The obtained results for α-particle pickup from both 6Li and 7Li give large values of α spectroscopic factors for some 10Be states, indicating their well-developed α + 6He cluster structure. The exotic two-proton pickup reaction (6He, 8Be) was studied, as well as two-neutron and triton transfer reactions. Quasi-free scattering of 6He on deuteron and α particle in 6Li was also observed. The sequential decay reactions 6He + 6Li → 6He + α + d, 6He + 6Li → 2α + t + n, 6He + 7Li → 6He + α + t, and 6He + 12C → 10Be + 2α were clearly seen, and α clustering of some states in 6,7Li, 8–10Be, and 14C was thus studied. Several new spectroscopic results obtained for some 10Be states support the existence of a molecule-like rotational band in 10Be with a very large moment of inertia.

Li-α CLUSTER STATES IN 12B USING 8Li + 4He INVERSE KINEMATICS ELASTIC SCATTERING

The 8Li elastic scattering on a 4He gas target was studied by means of the Inverse Kinematic Thick Target scattering method (TTIK) in order to investigate cluster configurations in excited states of 12B. A 8Li beam, at Ec.m. = 10.2 MeV, was provided by the EXCYT radioactive beam facility at Catania. The beam, while passing through the helium thick target decreases its energy, thus exploring the 8Li-α center-of-mass energy range 2.7 MeV≤ECM ≤9.6 MeV. Four ΔE-E silicon detector telescopes were used to detect the recoiling alpha particles. The time interval between the 8Li passing through a micro-channel plate foil, placed at the entrance of the chamber, and the detection of the α particles by the ΔE detectors was also measured. The time measurement allows to disentangle elastic from reactions events, otherwise impossible from energy measurements. This can be considered as an improvement of the TTIK method. In this paper the used experimental technique and the obtained preliminary results will be presented.

Resonant effects in the12C+12C?8Be gs +16O gs reaction aroundE cm=32.5 MeV

The12C+12C→8Begs+116Ogs reaction has been studied at c.m. energies of 27.9, 32.5 and 35.0 MeV. The energy dependence of the cross section is consistent with a resonant behaviour like the one observed for two12C nuclei excited in a very deformed state in the final channel. The angular distributions for the two reactions show also a similar oscillatory behaviour. The analysis suggests that the reaction proceeds through the formation of an intermediate state with a complex nature, involving largely deformed configurations as well as almost spherical ones.

The Inverse Kinematics Thick Target scattering method as a tool to study cluster states in exotic nuclei

The inverse kinematics thick target scattering method (TTIK) was used to measure the 8Li resonant elastic scattering on a 4He target in order to investigate 8Li-α cluster configurations in excited states of 12B. A 8Li beam at Ebeam = 30.6 MeV, provided by the radioactive beam facility EXCYT of LNS in Catania, while passing through a thick Helium target decreases continuously its energy. Thus, elastic scattering can be induced starting from the initial beam energy down to zero. Time of flight measurement between beam particles passing through a MCP detector and α-particles impinging on the ΔE stage of a Si telescope detector allows the discrimination of elastic scattering from nuclear reaction events, thus representing an improvement of the TTIK method. In this paper the used experimental technique and preliminary results will be described.

The (n, 3He) reactions on 40Ca and other nuclei at En = 14.6 MeV

Abstract A forward-angle part of the 40 Ca(n, 3 He 0 ) 38 Ar reaction angular distribution has been measured at E n = 14.6 MeV. The measured cross section is much higher than activation results for the (n, 3 He) reaction on some other nuclei. The differences between the cross sections of this reactions on different nuclei could be attributed mainly to Coulomb effects.

Quasifree processes in the3H+2H→d+d+n reaction

The quasifree scattering and reaction processes in the3H+2H→d→d+n interaction leaving a neutron as a spectator have been investigated at incident triton energies around 35 MeV. The results compare well with the predictions from Plane Wave Impulse Approximation, arbitrarily normalized to the data. The final energy prescription was used.

8Li+α resonant elastic scattering: a tool to study cluster states in 12B

The 8Li+4He elastic scattering excitation function was measured by using the inverse kinematic thick target method. The 8Li beam was provided by the LNS radioactive facility EXCYT at an energy of 30 MeV and it was delivered into a large scattering chamber filled with 4He gas. The detection system was made by three silicon telescopes and one MCP. This last detector was used to measure the number of incident particles as well as the time of flight allowing for the discrimination between elastic and inelastic scattering. The setup and the experimental technique will be described in details and the results, as well as the comparison of the data with an R-matrix calculation, will be shown and discussed.

Elastic scattering induced by halo nuclei

In this paper an overview of different results concerning elastic scattering in collisions induced by halo nuclei will be given. Due to the very low binding energy of such nuclei, coupling effects with the break-up channel have been found to be very important. Moreover, due to the long tail of the density distribution of halo nuclei and the presence of a large low-lying dipole strength distribution, long range absorption affects the elastic scattering angular distribution. In the paper the main effects responsible for the observed features in the scattering cross-section will be discussed.