A. Coc

Determination of the 13N(p, γ)14O reaction rate through the Coulomb break-up of a 14O radioactive beam

Abstract In stellar-evolution models, the 13N(p, γ)14O reaction plays an important role in the hot CNO cycle. Its reaction rate depends directly on the magnitude of the radiative width of the 5.17 MeV level in 14O. That width has been measured using the Coulomb break-up technique. A 70 MeV u 14O beam was excited in the Coulomb field of a 208Pb target, the 13N and proton fragments being recorded using a magnetic spectrometer and CsI scintillators, respectively. The experimental value Γγ = 2.4 ± 0.9 eV is in overall agreement with other recent measurements.

Astrophysical rate of the 11C+p reaction from the Coulomb break-up of a 12N radioactive beam

Abstract The Coulomb break-up technique has been used to determine the radiative width of one excited level in 12 N and the direct capture contribution to 11 C(p,γ) 12 N. The 12 N radioactive beam was produced through transfer and fragmentation reactions of a primary 95.5 MeV/u 14 N beam at GANIL. From the extracted cross section we deduce the rate of the 11 C+p reaction. Consequences for the hot pp chain are analysed.

Theoretical resolving power of a radiofrequency mass spectrometer

Radiofrequency mass spectrometers of L.G. Smiths type can reach a resolving power of 106–107 and a precision of 10−9–10−10. The resolving power, shape of peaks and limitations are described. As an example, the spectrometer to be used in an experiment aimed at measuring the p/p mass ratio is considered.

Comparison of low-energy resonances in15N(α,γ)19F and15O(α,γ)19Ne and related uncertainties

A disagreement between two determinations of Gamma_alpha of the astro- physically relevant level at E_x=4.378 MeV in 19F has been stated in two recent papers by Wilmes et al. and de Oliveira et al. In this work the uncertainties of both papers are discussed in detail, and we adopt the value Gamma_alpha=(1.5^{+1.5}_{-0.8})10^-9eV for the 4.378 MeV state. In addition, the validity and the uncertainties of the usual approximations for mirror nuclei Gamma_gamma(19F) approx Gamma_gamma(19Ne), theta^2_alpha(19F) approx theta^2_alpha(19Ne) are discussed, together with the resulting uncertainties on the resonance strengths in 19Ne and on the 15O(alpha,gamma)19Ne rate.A disagreement between two determinations of {Gamma}{sub {alpha}} of the astrophysically relevant level at E{sub x}=4.378 MeV in {sup 19}F has been stated in two recent papers by Wilmes {ital et al.} and de Oliveira {ital et al.} In this work the uncertainties of both papers are discussed in detail, and we adopt the value {Gamma}{sub {alpha}} = (1.5{sub {minus}0.8}{sup +1.5}){times}10{sup {minus}9} eV for the 4.378 MeV state. In addition, the validity and the uncertainties of the usual approximations for mirror nuclei {Gamma}{sub {gamma}}({sup 19}F){approx}{Gamma}{sub {gamma}}({sup 19}Ne), {theta}{sub {alpha}}{sup 2}({sup 19}F){approx}{theta}{sub {alpha}}{sup 2}({sup 19}Ne) are discussed, together with the resulting uncertainties on the resonance strengths in {sup 19}Ne and on the {sup 15}O({alpha},{gamma}){sup 19}Ne rate. {copyright} {ital 1997} {ital The American Physical Society}

Determination of α-widths in 19F relevant to fluorine nucleosynthesis

Abstract Nucleosynthesis of fluorine in the context of helium burning occurs through the 15 N(α,γ) 19 F reaction. At temperatures where fluorine formation takes place in most astrophysical models, the narrow resonance associated with the 4.378 MeV level of 19 F is expected to dominate the reaction rate, but its strength is not known. We used a 15 N confined gas target to study this level by means of the transfer reaction 15 N 7 Li,t) 19 F at 28 MeV. Reaction products products were analysed with a split pole magnetic spectrometer and the angular distributions for the first 16 levels of 19 F were extracted. These distributions are fairly well reproduced by FR-DWBA calculations in the framework of an α-cluster transfer model with a compound-nucleus contribution obtained by Hauser-Feshbach calculations. α-spectroscopic factors were deduced and, for unbound levels, the α-widths were determined and compared with the existing direct measurements. The α-width of the level of astrophysical interest ( E x = 4.378 MeV) was found to be Γ α = 1.5 × 10 −9 eV, a value 60 times smaller than the commonly used one. The astrophysical consequences for 19 F production in AGB stars are discussed.

The Orsay radio-frequency mass spectrometer

An RF mass spectrometer of the L. G. Smith type was built with 2 aims: to provide an experimental test of the CPT invariance (proton-antiproton mass comparison) and to measure the atomic masses of nuclei far from stability produced in the ISOLDE-PS Booster facility. As a priority was given to the first application, the features of the spectrometer are presented in this framework. Then, a discussion is made about the adaptation, currently under way, to the second application.

Field mapping and corrections of the magnet of a radio-frequency mass spectrometer

Abstract The design of the magnet for a radio-frequency mass spectrometer with resolving power in the range 105 to 106 is presented. The required homogeneity and initial physical characteristics of the magnet are summarized. Then, the experimental methods which have been used for field mapping and field corrections are explained. Final performances of the magnet homogeneity are given, which already provide a resolving power of 3×105, in agreement with the original goal.

The 18F(p,α)15O reaction rate for application to nova γ-ray emission

The 18F(p,α)15O reaction is recognized as one of the most important reaction for nova gamma–ray astronomy as it governs the early ⩽ 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low–energy resonance strengths. We report here on our lastest results concerning the study of the D(18F,pα)15N reaction, as well as on the determination of the 18F(p,α)15O reaction rate using the R-matrix theory. Remaining uncertainties are discussed.

31S(p,γ)32Cl reaction in explosive hydrogen burning

Abstract In the present work we attempted to determine excitation energies and widths of proton unbound states in 32 Cl. These states may contribute as resonances to the 31 S(p,γ) reaction and will determine the reaction rate. Results were used to evaluate the reaction flow in the Si to Ar region obtained by nova outbursts in the case of an ONeMg white dwarf of 1.35 M ⊙ .

Antiproton-proton mass comparison with a radio-frequency mass spectrometer

Abstract The experiment aims at the reduction of the upper limit on a hypothetical CPT violation in the antiproton-proton system. A radio-frequency mass spectrometer (RFMS) has been designed and built to make the comparison of the charge to mass ratios of p and p by measuring the ratios of the cyclotron frequencies of p and H− ions. At present, the RFMS is installed on-line to the LEAR facility at CERN. The resolving power has been found to be close to 3 × 105 and it still could be improved. A decelerating system (RFQ) has been installed in order to decelerate antiprotons from 2 MeV to 200 keV and to match as well as possible the acceptance of the spectrometer. It is presently under test and data taking should take place in 1992.