S. Cherubini

Louvain-Edinburgh Detector Array (LEDA): a silicon detector array for use with radioactive nuclear beams

We discuss the design and implementation of the Louvain-Edinburgh Detector Array: a charged particle detector array composed of silicon-strip detectors which is used for the study of nuclear astrophysics and nuclear physics using radioactive nuclear beams at the Louvain-1a-Neuve radioactive nuclear beam facility

CD: A double sided silicon strip detector for radioactive nuclear beam experiments

A very compact double sided silicon strip detector array is described, designed for use in reaction studies involving radioactive nuclear beams. It is small enough to fit inside a large solid angle g-detector array and will enable Dopplershift corrections at energies in the vicinity of the Coulomb barrier. The detector provides sufficient energy and time-offlight resolution for the identification of light reaction products and can be set up to cover a substantial part of the scattering angular distribution with good resolution. The device is available in thicknesses of up to 500 mm to stop all interesting reaction products. Moreover, a very thin (35–40 mm) variant of this detector is described that can be used as an energy loss detector in a DE@E telescope geometry followed by a detector that measures the residual energy. This provides additional particle identification capabilities, e.g. in light exotic nuclei induced reactions. First results from a commissioning run using a post-accelerated radioactive beam are presented. r 2002 Elsevier Science B.V. All rights reserved.

Long range absorption in the scattering of 6He on 208Pb and 197Au at 27 MeV

Quasi-elastic scattering of 6He at E_lab=27 MeV from 197Au has been measured in the angular range of 6-72 degrees in the laboratory system employing LEDA and LAMP detection systems. These data, along with previously analysed data of 6He + 208Pb at the same energy, are analyzed using Optical Model calculations. The role of Coulomb dipole polarizability has been investigated. Large imaginary diffuseness parameters are required to fit the data. This result is an evidence for long range absorption mechanisms in 6He induced reactions. Comment: 10 pages, 10 figures, minor corrections. To appear in Nucl. Phys. A

Elastic 2n-transfer in the 4He(6He,6He)4He scattering

The elastic scattering He-4(He-6,He-6)He-4 has been investigated at center-of-mass energies of 11.6 and 15.9 MeV. Differential cross sections are determined using a post-accelerated He-6 (T-1/2 = 0.807 s) beam in the center-of-mass angular range between 50 and 140 degrees. The comparison of the measured data with calculations using a double folding potential shows evidence for the 2n-transfer process in the He-4(He-6,He-6)He-4 elastic scattering

The alpha-C-12 scattering studied via the Trojan-Horse method

Abstract: The Trojan-horse method has been suggested as a means to study a two-body reaction at astrophysical energies via a three-body breakup reaction. In order to test this method the 6Li(12C,α12C)2H reaction was studied in a kinematically complete experiment at an incident energy of 18 MeV. Coincidence spectra show the presence of the quasi-free α-12C scattering process. The excitation function of the three-body reaction is calculated in the plane wave impulse approximation assuming quasi-free scattering and is compared with the experimental data. Also, the excitation function of the virtual α-12C elastic scattering is extracted from the three-body reaction cross section at low deuteron momenta and compared with the behaviour of the free scattering cross section.

Low-energy radioactive ion beam induced nuclear reactions

Low-energy post-accelerated radioactive ion beams have been used to study nuclear reactions addressing important nuclear structure and nuclear astrophysics questions. A high-granularity, large-solid-angle silicon strip detector array has been used to account for the low reaction products yields. First experiments using a He-6 beam on thin C-12 targets show the feasibility of direct reaction studies with good angular resolution and a detection limit in access of 0.1 mb sr(-1) cross sections. The measurement of the six alpha-decay channel in a N-13-induced reaction on a B-11 target shows the capabilities of this experimental technique even for sophisticated reaction studies. The study of stellar properties in ground-based experiments, in particular break-out reactions from the hot-CNO, i.e. O-15(alpha, gamma) Ne-19, can be pursued using these beams. Experiments are being performed to study these reactions by measurement of d(Ne-18, p) Ne-19*(alpha)O-15 and alpha(Ne-18, p), which might provide an alternative breakout route.

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.

Investigation of (α, p) reactions using a radioactive beam

Abstract Reactions such as 18 Ne(α, p) 21 Na of importance to Nuclear Astrophysics may be studied directly through the use of a radioactive beam and a gaseous helium target. A system to study such reactions has been developed and tested using the 13 N beam available at the Radioactive Ion Beam facility (RIB) at Louvain-la-Neuve. This ( α , p ) reaction was chosen as previous studies of the inverse reaction 16 O(p, α) 13 N allowed the resonance strength of a strong resonance at 8.07xa0MeV (Tilley et al., Nucl. Phys. A 564 (1993) 139) in the compound nucleus 17 F to be calculated and compared with that obtained through experiment. These resonance strengths showed good agreement and so validated the technique for further work.

Structure effects on reaction mechanisms in collisions induced by radioactive ion beams

The present paper concerns the study of reactions induced by radioactive beams of halo and weakly bound nuclei at energies around and above the Coulomb barrier. The results obtained for the reaction induced by the halo nucleus 6He on 64Zn have been compared with the results for the reaction induced by 4He on the same target. The results of the reaction induced by the weakly bound unstable 13N on the weakly bound 9Be have been compared with those for the reaction 10B + 12C.

Indirect study of 19Ne states near the F18+p threshold

Abstract The early E ⩽ 511 keV gamma-ray emission from novae depends critically on the F 18 ( p , α ) O 15 reaction. Unfortunately the reaction rate of the F 18 ( p , α ) O 15 reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the F 18 + p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d ( F 18 , p ) F 19 ( α ) N 15 transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the F 18 ( p , α ) O 15 and F 18 ( p , γ ) Ne 19 reaction rates.