Marc Loiselet

A Direct Measurement of the F-18(p,Alpha)o-15 Reaction

The cross section for the F-18(p,alpha) O-15 reaction has been obtained in reverse kinematics (F-18 beam on CH2 target) between 550 and 740 keV above threshold, i.e. in a region of astrophysical interest. The reaction yield is dominated by a wide resonant state whose spin, parity, total width and partial widths were deduced from the analysis of the alpha-particle and elastic proton data.

Experimental determination of the 7Be+p scattering lengths

The Be-7 + p elastic cross section has been measured at the Centre de Recherches du Cyclotron RIB facility at Louvain-la-Neuve in the c.m. energy region from 0.3 to 0.75 MeV by bombarding a proton-rich target with a radioactive 7Be beam. The recoil protons have been detected in the angular range theta(c.m.) = 120.2degrees-131.1degrees and theta(c.m.) = 156.6degrees-170.2degrees using the LEDA system. From a R-matrix analysis of the cross section data. we obtain the energy and the width of the I resonance (E-X = 0.77 MeV). The iota = 0 scattering lengths a(01) = 25 +/- 9 fm (channel spin I = 1) and a(02) = -7 +/- 3 fm (channel spin I = 2) have been deduced. They are compared to values expected from charge-symmetry properties. Implications on the low energy S-factor of the Be-7(p,gamma)B-8 reaction are discussed

Two proton emission induced via a resonance reaction

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.

D(F-18, p alpha) N-15 reaction applied to nova gamma-ray emission

The 18F(p,alpha)15O reaction is recognized to be one of the most important reactions for nova gamma-ray astronomy as it governs the early E <= 511keV gamma emission. However in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction, induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or alpha-particles) were detected in coincidence in two silicon strip detectors. A DWBA analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O reaction.

Recent results from the Louvain-la-Neuve RIB-facility

At the end of 1999, a first on-line RIB was accelerated, extracted and separated with the new cyclotron, CYCLONE44. An efficiency of 7% (from ion source exit to experiment target), resulting in 6 x 10(8) pps of Ne-19(3+), was obtained. Up to 9 kW of beam power has been put on the LiF target giving increased intensities for He-6, Ne-18 and O-15. A new accelerated and pure Be-7-beam of 2 x 107 pps has been produced, using the sputteting electrode in the ECR-source. Production tests of 140 using CYCLONE110 have started in view of their acceleration with CYCLONE44

The 18F(p,α) reaction and its astrophysical implications

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

Towards high-resolution laser ionization spectroscopy of the heaviest elements in supersonic gas jet expansion

Resonant laser ionization and spectroscopy are widely used techniques at radioactive ion beam facilities to produce pure beams of exotic nuclei and measure the shape, size, spin and electromagnetic multipole moments of these nuclei. However, in such measurements it is difficult to combine a high efficiency with a high spectral resolution. Here we demonstrate the on-line application of atomic laser ionization spectroscopy in a supersonic gas jet, a technique suited for high-precision studies of the ground- and isomeric-state properties of nuclei located at the extremes of stability. The technique is characterized in a measurement on actinium isotopes around the N=126 neutron shell closure. A significant improvement in the spectral resolution by more than one order of magnitude is achieved in these experiments without loss in efficiency.

Production of a high purity F-18 radioactive beam

An efficient method for the production and post-acceleration of a pure F-18(T-1/2 = 109.8 min) radioactive beam has been developed. Large amounts of F-18 are produced via the O-18(p,n)F-18 reaction using a 15.5 MeV proton beam on an O-18-enriched water target. After the chemical purification of the target content, the F-18 activity is transferred into [F-18]-fluoromethane. It is then transported to an ECR ion source, where after dissociation of the molecules, the fluorine atoms are ionized. Finally, the F-18(2+) ions are accelerated to 14 MeV in a second cyclotron. The different steps in the production cycle and the characteristics of the final F-18 beam are discussed

Production, acceleration and use of radioactive ion beams at Louvain-la-Neuve

The production and acceleration of radioactive beams using two cyclotrons coupled by an electron cyclotron resonance ion source is described. Pure beams of N-13 (T1/2 = 9.96 min) and Ne-19 (T1/2 = 17 s) with an energy around 1 MeV/amu are obtained with intensities larger than 50 ppA. As an example, cross section measurements using a N-13 beam on hydrogen and deuteron targets are presented. Finally, the ARENAS3 project, a future plan for the production of radioactive beams in Belgium, is described.

Graphite target for the SPIRAL project

We present here a study of the thermal and physical properties of graphite targets for the SPIRAL project. The main objective was to develop an optimized set-up both mechanically and thermally resistant, presenting good release properties (hot targets with thin slices). We show here the results of irradiation tests concerning the mechanical and thermal resistance of the first prototype of SPIRAL target with conical geometry. We also study the micro-structural properties of the graphite target in order to check that the release properties are not deteriorated by the irradiation. Finally, we present the results concerning the latest pilot target internally heated by an electrical current. This setup has been especially designed to be used in case of low power primary beams.