J.-P. Thibaud

New measurement and analysis of the7Be(p,γ)8B cross section

Cross sections for the 7Be(p,γ)8B reaction have heen measured for Ec.m. = 0.35-1.4 MeV using radioactive 7Be targets. Two independent measurements carried out with different beam conditions, different targets, and detectors are in excellent agreement. A statistical comparison of these measurements with previous results leads to a restricted set of consistent data. The deduced zero-energy S factor S(0) is found to be 15%-20% smaller than the previously recommended value. This implies a 8B solar neutrino flux lower than previously predicted in various standard solar models.

Low-energy measurement of the Be-7(p,gamma) B-8 cross-section

We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm = 185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies. Comment: Accepted for publication in Phys. Rev. Lett

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.

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}

[TSUP]6[/TSUP]L[CLC]i[/CLC] from Solar Flares

By introducing a hitherto ignored 6Li producing process, due to accelerated 3He reactions with 4He, we show that accelerated particle interactions in solar flares produce much more 6Li than 7Li. By normalizing our calculations to gamma-ray data, we demonstrate that the 6Li produced in solar flares, combined with photospheric 7Li, can account for the recently determined solar wind lithium isotopic ratio, obtained from measurements in lunar soil, provided that the bulk of the flare-produced lithium is evacuated by the solar wind. Further research in this area could provide unique information on a variety of problems, including solar atmospheric transport and mixing, solar convection and the lithium depletion issue, and solar wind and solar particle acceleration.

Gamma-ray Lines of Carbon and Oxygen from Orion

The gamma-ray lines from the Orion complex observed by the COMPTEL instrument are interpreted as related to the de-excitation in flight of accelerated oxygen and carbon in a molecular cloud, essentially composed of hydrogen and helium. The shape and the intensity of the lines are two constraints for any hypothesis concerning the acceleration/injection process. Using an update of the involved gamma-production cross sections, two models of acceleration are examined, leading to a shock spectrum or a supernova spectrum for the accelerated carbon and oxygen. Although the actual error bars in the published COMPTEL spectrum are too large to draw firm conclusions at this stage, our interpretation of the COMPTEL data is in better agreement with a spectral shape related to the ejection of those nuclei by a Type Ic supernova.

6Li from Solar Flares.

By introducing a hitherto ignored 6Li producing process, due to accelerated 3He reactions with 4He, we show that accelerated particle interactions in solar flares produce much more 6Li than 7Li. By normalizing our calculations to gamma-ray data, we demonstrate that the 6Li produced in solar flares, combined with photospheric 7Li, can account for the recently determined solar wind lithium isotopic ratio, obtained from measurements in lunar soil, provided that the bulk of the flare-produced lithium is evacuated by the solar wind. Further research in this area could provide unique information on a variety of problems, including solar atmospheric transport and mixing, solar convection and the lithium depletion issue, and solar wind and solar particle acceleration.

A 250 kV high current ion accelerator for applications in nuclear astrophysics

Abstract A 250 kV ion accelerator which provides high proton beam currents of the order of 1 mA has been built at the CSNSM, Orsay. Energy spread and energy stability were found to be better than ± 50 eV. This accelerator will be used for precise determination of proton induced nuclear reactions at low energies relevant in the field of nuclear astrophysics. Experimental studies of nuclear reactions involving radioactive targets will be performed. The target setup for measuring particle emitting reactions consists of a solenoidal superconducting spectrometer to achieve a large solid angle for the detection of the reaction products and an improved signal/noise ratio.

Determination of alpha widths in 19F

The reaction 15Na(α,γ)19F is of great importance for fluorine nucleosynthesis. At temperatures where 19F is expected to be produced, the narrow resonance associated with the 4.377 MeV level of 19F yields the dominant contribution to cross section. We have extracted its width by using the alpha‐transfer reaction 15N(7Li,t)19F and finite range DWBA analysis.

ONeMg Novae: Nuclear uncertainties on the 26Al and 22Na yields

The influence of the nuclear uncertainties on the reaction rates involved in 26Al and 22Na production in ONeMg novae are discussed. A semi‐analytical model of novae envelope is used with an improved calculation of the time evolution. Comparison is made with the results of hydrodynamical models.