Neutron induced reactions on radioactive beryllium and argon isotopes

The preparation of radioactive $^{10}$Be, $^{37}\!$Ar and $^{39}\!$Ar samples is discussed. Investigation of the $^{10}$Be(n$_{th} , \gamma$)$^{11}\!$Be , $^{37}$Ar(n$_{th} , \alpha$)$^{34}$S , $^{37}$Ar(n$_{th}$ , p)$^{37}\!$Cl and $^{39}\!$Ar(n$_{th} , \alpha$)$^{36}$S reactions is reported, and resonances in the $^{37}$Ar(n , $\alpha$)$^{34}$S reaction have been observed and analysed

Thermal neutron induced (n,p) and (n,alpha) reactions on 37Ar

The 37Ar(n_th,alpha)34S and 37Ar(n_th,p)37Cl reactions were studied at the high flux reactor of the ILL in Grenoble. For the 37Ar(n_th,alpha_0) and 37Ar(n_th,p) reaction cross sections, values of (1070+/-80)b and (37+/-4)b, respectively, were obtained. Both values are about a factor 2 smaller than results of older measurements. The observed suppression of the 37(n_th,alpha_1) transition could be verified from theoretical considerations. Finally, evidence was found for the two-step 37Ar(n_th,gamma-alpha) process.Comment: 11 pages, 5 figures, accepted for publication in Nuclear Physics

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges, Spain, 20-24 May 2002, 5 pages, 3 figure

Indirect study of 19Ne states near the 18F+p threshold

The early E < 511 keV gamma-ray emission from novae depends critically on the 18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the 18F+p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d(18F,p)19F(alpha)15N 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 18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics

D(18F,pa)15N 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.Comment: Rapid Communication to appear in Phys. Rev. C., 4 pages and 4 figure

ECR ion sources and rare isotope beams at Louvain-la-Neuve

Electron cyclotron resonance (ECR) ion sources are used in a variety of applications. A lot of them are put to work to ionize abundant isotopes at high intensity and/or high charge states. But another important field for these kinds of sources is also to ionize, with high efficiency, isotopes which are available only in very small quantities, e.g., radioactive isotopes or stable isotopes with very small abundances. At Louvain-la-Neuve a range of different "exotic" beams are accelerated using two types of ECR ion sources. Each element requires the use of some unique method in preparing, operating, or tuning the source. Examples of the use of ECR sources for gaseous exotic isotope ionization include: the production of low charge state Ar-37 (t(1/2)=35 days) and 170 (natural abundance 0.038%) for implantation purposes and short-lived He-6 (t(1/2)=0.8 s) for postacceleration. The sputtering method has been used for the production of Ni-64 beams (0.91% natural abundance) and Be-7 beams (t(1/2)=53 days). Some aspects of the tuning, preparation, and performance of the ECR sources and the configuration and preparation of the sputtering apparatus will be discussed. (C) 2002 American Institute of Physics

Realization of Nuclear Targets by Ion Implantation. The 17O Case.

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel

Preparation of highly enriched O-17 samples for neutron-induced reaction studies

Suitable O-17 samples are required for the study of the O-17(n,alpha)C-14 reaction with various detectors, The electrospraying of metal oxides enriched in O-17 onto an Al substrate yielded negative results: no O-17(n(th),alpha) reactions were observed when irradiating these samples with thermal neutrons, These tests demonstrated the need to minimize the B-10 content in sample and backing, since the B-10(n(th),alpha(1)) reaction causes a strongly disturbing background. Good results were obtained in the reactor experiments using gaseous samples (O-17 enrichments of 58.2%, 72.1% and 85.5%) with a dedicated experimental setup. The experimental conditions being quite different at accelerators, an alternative method was developed to prepare samples suited for use in ionization chambers, For this purpose, O-17 ions were implanted in ultra-pure Al foils. The thickest sample prepared in this way contains 8 x 10(18) atoms of O-17, with a B-10/O-17 ratio of 10(-4). (C) 2001 Elsevier Science B.V. All rights reserved

The 17O(n,alpha)14C Reaction from Subthermal up to Approximately 350 keV Neutron Energy.

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel