G. Vancraeynest

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.

STATUS-REPORT OF THE LEUVEN ISOTOPE SEPARATOR ONLINE (LISOL)

Abstract The mass separator LISOL, on-line to the CYCLONE cyclotron, is described as it is presently configured. Improvements in the cyclotron beams are mentioned, and separator developments to accommodate the various experimental stations are presented. Modifications to the separator to permit ion guide operation are given. Yields of some short-lived isotopes are presented, for heavy-ion induced reactions.

Optimisation and modelling of electrochemically etched polycarbonate track detectors

Abstract Electrochemically etched polycarbonate nuclear track detectors have been used to detect the β-delayed α-decay of the 20 Na nuclei that were produced in the study of the astrophysically important 19 Ne(p,γ) 20 Na reaction. The application required preceding investigations and developments. The insensitivity to β-radiation has been confirmed in off-line irradiations with β-sources up to doses of 20000 Gy. The density of intrinsic background tracks has been reduced to a mean value of 1.3 ± 0.1 cm −2 . The response function for α-detection as a function of energy and angle of incidence has been determined using Rutherford backscattered α-particles. A model for electrochemical etching that is generally valid for all ions and plastic detectors has been developed. It successfully reproduced the measured response function and track diameters.

New limits for the Ne-19(p,gamma)Na-20 astrophysical reaction rate from direct measurements using radioactive beams

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.

The Ne-19(p,gamma)Na-20 astrophysical reaction rate determined from measurements with a radioactive beam

The Ne-19(p,gamma)Na-20 as well as the Ne-19(d,n)Na-20 reaction have been studied in inverse kinematics using Ne-19 radioactive beams. Upper and lower limits for the Ne-19(p,gamma)Na-20 astrophysical reaction rate have been deduced, for the first time on the basis of direct experimental data. It is concluded that the transition from the hot-CNO cycle to the rp-process in explosive hydrogen burning is most likely governed by the preceeding O-15(alpha,gamma)Ne-19 reaction.

Nuclear reactions of astrophysical interest with radioactive beams

The ARENAS(3) facility, coupling the two cyclotrons of Louvain-la-Neuve, is intensively been used over the past years for cross-section measurements of nuclear reactions of astrophysical interest. We will describe the characteristics of the available beams and the experiments going on using these beams. The Ne-19(p,gamma)Na-20 reaction, of considerable importance for the reaction now between the CNO and the NeNa mass region in high-temperature hydrogen burning conditions, will be discussed in particular. The proposed low-energy resonance at 0.447 MeV has been measured in inverse kinematics using novel activation techniques. An upper limit (90% C.L.) of 18 meV is obtained for the strength of this first particle-unbound state of Na-20 together with preliminary values for the strength of the higher excited states.

Production and Use of Post-accelerated Radioactive Nuclear Beams

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 m) and Ne-19(Tl 2=17 s) with an energy between 0.5 and 4.0 MeV/amu are obtained. The first experiments using these energetic radioactive beams are discussed and the ARENAS3 project is very briefly outlined.

Elastic transfer in 4He(6He,6He)4He

We have investigated the reaction {sup 4}He({sup 6}He,{sup 6}He){sup 4}He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the {sup 6}He-{sup 4}He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two {sup 4}He cores.We have investigated the reaction 4He(6He,6He)4He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the 6He-4He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two 4He cores.

Elastic transfer in

We have investigated the reaction {sup 4}He({sup 6}He,{sup 6}He){sup 4}He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the {sup 6}He-{sup 4}He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two {sup 4}He cores.We have investigated the reaction 4He(6He,6He)4He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the 6He-4He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two 4He cores.

Elastic transfer in {sup 4}He({sup 6}He,{sup 6}He){sup 4}He

We have investigated the reaction {sup 4}He({sup 6}He,{sup 6}He){sup 4}He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the {sup 6}He-{sup 4}He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two {sup 4}He cores.We have investigated the reaction 4He(6He,6He)4He at c.m. energies of 11.6 and 15.9 MeV and determined the differential elastic cross section in the angular range between 50 and 145 degree. The comparison of the measured data with DWBA calculations using a double folding potential for the 6He-4He scattering shows evidence for the elastic transfer of a di-neutron cluster between the two 4He cores.