A. Lefebvre

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.

Measurement of the {sup 24}Mg({sup 3}He,p){sup 26}Al cross section: Implication for {sup 26}Al production in the early solar system

The nucleosynthetic origin of {sup 26}Al (t{sub 1/2}=0.72 Myr) in the early solar system is still an open question. Several models predict that short-lived radionuclides could be produced by irradiation of circumsolar material by light charged particles emitted by the young sun. Within some models, most of the {sup 26}Al is produced by {sup 3}He-induced reactions on {sup 24}Mg. Little experimental data exist on {sup 3}He reactions so that irradiation models have had to rely on theoretical cross sections deduced from statistical nuclear reaction codes. We performed a direct measurement of the {sup 26}Al production on Mg target by means of {gamma} ray spectroscopy and accelerator mass spectrometry (AMS). The data indicate that the theoretical cross section used in previous approaches was overestimated by a factor of 3. Taking the particle spectra considered in theoretical approaches these data lead to a net reduction of the {sup 26}Al production of a factor of 2. We calculated the relative contribution of the different {sup 26}Al production channels depending on the irradiation scenario. We show that extremely large particles fluxes would be necessary to reach the canonical {sup 26}Al/{sup 27}Al =5x10{sup -5} in solids that were present in the early solar system. Anmorexa0» in situ origin of this important isotopic chronometer by irradiation is unlikely.«xa0less

Study of the 18F(p,α)15O reaction for application to nova γ-ray emission

Abstract The 18 F(p,α) 15 O 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. In order to better constrain this reaction rate, we have studied the one-nucleon transfer reaction, D( 18 F,pα) 15 N, at the CRC-RIB facility at Louvain La Neuve.

New7Be(p, γ)8B cross section measurement

The7Be(p,γ)8B cross section has been re-measured using radioactive targets. The zero-energy astrophysical S-factor is found significantly lower than the previously adopted value.