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The He-6+Li-6,Li-7 and He-6+C-12 scattering and reactions have been studied using a 18 MeV He-6 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 Li-6 scattering on the same targets and at close energies. Large cross sections are observed for a-transfer reactions to some states of Be-10. The sequential decay reactions He-6+Li-6-->He-6+alpha+d, He-6+Li-6-->2alpha+t+n, He-6+Li-7-->He-6+alpha+t and He-6+C-12-->Be-10+2alpha, were clearly seen and analysing them alpha-clustering of some states in Li-6, Li-7, Be-8, Be-9, Be-10 and C-14 was recognized.

The elastic-scattering, neutron transfer and projectile break-up channels have been studied for the reaction He-6 + Zn-64 at energies around the Coulomb barrier. The results show a very large break-up and transfer cross-section corresponding to the largest fraction of the total reaction cross-section. No evidence of threshold anomaly emerged from the elastic-scattering optical-model analysis.

The reaction N-13 + B-11 has been investigated at two 13N beam energies: 29.5 and 45 MeV, Charged particles and gamma rays emitted in the reactions have been detected using a large array of silicon strip detectors and BaF2 scintillators, respectively. Several reaction channels have been analysed with different aims. The proton transfer reaction B-11(N-13, C-12)C-12 to various excited states of C-12 has been studied to obtain information on the N-13(g.s.) structure. The excitation energy of the Mg-24 compound nucleus was in the region where several resonances occur in the C-12 + C-12 system. The six-alpha decay of the Mg-24 intermediate system has been studied. Some of these events have been identified as coming from the break-up of two C-12* in the 3(1)(-)-3(1)(-) and 3(1)(-)-0(2)(+) states. The total fusion cross section has also been extracted from the data. In order to extract information on the isospin purity/mixing in Mg-24 at high excitation energy (E-x similar to 47 MeV), the GDR gamma emission from this self-conjugate nucleus has been studied. A comparison of gamma spectra has been undertaken for the reactions N-13 + B-11 and N-14 + B-10. (C) 2001 Elsevier Science B.V, Ail rights reserved.

For the first time Borromean nucleus induced reactions have been measured below the three-body breakup threshold. A set of angular distributions for the single and two neutron transfer as well as on the charge exchange reaction channel has been obtained. The experimental data have sufficient angular coverage and precision to allow for the discrimination between different model predictions, which do not suffer from ambiguities introduced to the interpretation of experimental data due to flux losses into the three-body breakup channel. The viability of the idea is demonstrated in the case of nuclear reactions induced by the simplest Borromean nucleus, i.e., He-6, on a structureless target, i.e., protons. Comparison with different theoretical approaches suggest that coupled channel effects play an important role. A decrease of the model wave function's rms radius of 0.15 fm alters the predicted angular distributions such that they no longer follow the experimental results.

Post-accelerated radioactive ion beams produced at Louvain-la-Neuve, Belgium have been used to investigate the O-15(alpha,gamma)Ne-19 reaction, which is generally considered as the potential breakout reaction from the hot CNO cycle. This reaction may not only lead to the synthesis of proton-rich nuclei via the rp-process, but is also thought to initiate the massive release of energy which can trigger stellar explosions such as novae and Xray bursters. The properties of this reaction have been investigated via a study of the relevant decays of excited states in Ne-19, which were populated using an inverse Ne-18(d,p) reaction. The measurements were aimed at the determination of branching ratios which, combined with knowledge of the total width of the states under investigation, allow for the modelling of the O-15(alpha,gamma)Ne-19 reaction rate. The result for the branching ratio of the E-R=4.600MeV state is found to be in good agreement with an alternative approach. The experiments have been carried out using an especially designed high granularity large solid angle silicon strip detector array consisting of 320 elements to compensate for the high decay background and limited intensity of this radioactive beam environment. The method and experimental set-up will be presented. The decay properties of selected populated resonances will be discussed. An upper limit of 10(-2) for the branching ratio of the astrophysically important state at 4.033MeV was obtained.

The present work aims to extend the experiment reported in refs. [1] and [2] concerning the Ne-18(alpha, p)Na-21 reaction, by making a measurement at a lower energy (1.50-3.00 MeV in the centre-of-mass frame of the Ne-18 + alpha system) in an attempt to observe other states in the level structure of Mg-22 below 10.57 MeV. A direct measurement of the energy loss of the Ne-18 beam, as it passed through He gas, was undertaken to reduce one source of uncertainty in the determination of the stellar reaction rate. The experiment was undertaken at the radioactive ion beam facility at Louvain-la-Neuve.

We present here the first results obtained with the new recoil separator ARES. ARES is used for the measurement of (p,gamma) and (alpha,gamma) reactions at astrophysical energies in inverse kinematic using both stable and radioactive beams.

The O-15(alpha,gamma) reaction could offer an escape from the hot-CNO cycle if its cross-section at the relevant energies is sufficiently high. In order to indirectly measure it, an experiment based on the Ne-18(d,p) process was performed in Louvain la Neuve.

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. (C) 2000 Elsevier Science B.V. All rights reserved.

Using the generalized optical theorem for charged particles, the total reaction cross section sigma(R) and the nuclear scattering amplitude f(N) at 0 degrees have been determined model independently for the first time in the He-6+C-12 system. A large fraction of sigma(R), is accounted for by f(N)(0 degrees) -a manifestation of the nuclear forward glory effect. A comparison with the Li-6+C-12 system supports the prediction that the high break-up probability of He-6 reduces the fraction of the total reaction cross section accounted for by the nuclear scattering amplitude at 0 degrees. [S0556-2813(99)03011-3].

The six-ct decay of Mg-24 has been studied via the reaction N-13+ B-11 at two beam energies, 29.5 MeV and if 45 MeV. Large detector arrays allowed this reaction to be studied with low intensity radioactive N-13 beam. The excitation energy in the Mg-24* was in the region of the 46 MeV resonance in C-12+C-12 scattering. From the six-a particles, events of interest were selected by associating two of the a particle pairs as the decay products of Be-8. The c.m. energy spectra for two Be-8 + two alpha events have been extracted. The analysis revealed that most of these events originate from C-12(31)- + C-12(31)-. The total cross section for these six-alpha events has been extracted at the two beam energies. [S0556-2813(99)06902-2].

The transfer reaction B-11(N-13,C-12)C-12* has been investigated at the two laboratory energies E-lab = 45 MeV and E-lab = 29.5 MeV. Particle-gamma and particle-particle coincidences have been measured. The coincidence between a heavy ion and the 15.1 MeV gamma-ray emitted from C-12* shows transition to the C-12(gs) + C-12*(15.1) and C-12*(4.44) + C-12*(15.1) exit channels. These indicate the mixed ground-state structure of N-13. DWBA calculations have also been performed. Analysis of particle-particle coincidence data revealed the presence of transfer channels also to unbound states of C-12 such as C-12(gs) + C-12* (E* > 7.64 MeV) and C-12*(4.44) + C-12* (E* >7.64 MeV). The angular distributions have been extracted for these two channels. Six-alpha-particle events have also been analyzed. Some of these events have been identified as coming from B-11(N-13,C-12*)C-12* reaction. An enhancement in the six-alpha cross-section is observed at an excitation energy for the compound nucleus Mg-24 close to the 46 MeV resonances observed in C-12+C-12 inelastic scattering. These six-alphas events are generated mostly from the break-up of C-12(3(1)(-))+(12) C(3(1)(-)) and therefore seems not to be associated with the six-alphas chain state.

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.

F-18 radioactive beams were used to measure the F-18(p,alpha) reaction in the c.m. energy ranges of 265-535 keV and 550-740 keV. In each case, a resonant level was clearly detected, of which the resonant strength and some other properties were deduced. The astrophysical reaction rate was calculated down to the novae peak temperature. Consequences for the hot CNO cycles were drawn. (C) 1997 Elsevier Science B.V.

A radioactive beam of N-13 ions was used to bombard a (CH2)(n) target in order to populate a narrow resonance at 7.77 MeV in O-14. A weak two proton decay branch was observed with a width of 125 +/- 20 eV which occurs predominantly by a sequential mechanism. A limit for He-2 emission of Gamma(2He) < 6 eV is compared with calculations.

Inexplosive stellar hydrogen burning, the hot CNO cycles and the rp-process are mainly linked by the reaction sequence O-15(alpha,gamma) Ne-19(p,gamma)Na-20. Using intense Ne-19 radioactive beams, both the Ne-19(p,gamma) and the Ne-19(d,n) reaction have been studied. Upper and lower limits for the Ne-19(p,gamma) reaction rate have been deduced, allowing to conclude that the O-15(alpha,gamma) reaction is most likely the bottleneck reaction.