C. Iliadis

Information about the 12C(α,γ)16O reaction from the β-delayed proton decay of 17Ne

We are studying the β-delayed proton decay of 17Ne with the goal of determining the E2 part of the 12C(α,γ)16O cross section at energies relevant to helium burning in stars. We have determined branching ratios for proton and α-decay for states in 17F from 8.08 to 11.193 MeV. In addition, we have observed the break-up of the isobaric analogue state (IAS) at 11.193 MeV into three particles via two channels: proton decay to the 9.59 MeV state in 16O which breaks up into an α-particle plus 12C; and α-decay to the 2.365 MeV state in 13N which breaks up into a proton plus 12C. This is the first reported observation of the decay of the IAS to the 1− state in 16O at 9.59 MeV.

Thermonuclear reaction rate of 18 O( p , ? ) 19 F

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as cool bottom processing (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented.

Investigation of the 12C(α, γ)16O reaction via the β-delayed proton decay of 17Ne

Abstract We have determined the branching ratios for the β-delayed proton decay of excited states in 17 F to excited states in 16 O by measuring proton-γ-ray coincidences. We have observed transitions to the 2 + state at 6.917 MeV in 16 O from 17 F states at 11.193, 10.0, 9.45, 8.83 and 8.44 MeV. In particular, the transition from the 9.45 MeV state is an order of magnitude stronger than the accompanying transitions to the 1 − state at 7.117 MeV and the 3 − state at 6.130 MeV, and seems a favourable case for the observation of 16 O break-up into α + 12 C .

Thermonuclear reaction rate of18O(p,γ)19F

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as cool bottom processing (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented.

Thermonuclear reaction rate of 18O(p,gamma)19F

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as cool bottom processing (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented.

Thermonuclear reaction rate of 18 O( p , γ ) 19 F

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as cool bottom processing (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented.

Measurement of {sup 17}O(p,gamma){sup 18}F between the narrow resonances at E{sub r}{sup lab}=193 and 519 keV

The {sup 17}O(p,gamma){sup 18}F reaction sensitively influences hydrogen burning nucleosynthesis in a number of stellar sites, including classical novae. These thermonuclear explosions, taking place in close binary star systems, produce peak temperatures in the range of T=100-400 MK. Recent results indicate that the thermonuclear rates for this reaction in this particular temperature range are dominated by the direct capture process. We report on the measurement of the {sup 17}O(p,gamma){sup 18}F cross section between the narrow resonances at E{sub r}{sup lab}=193 and 519 keV, where the S factor is expected to vary smoothly with energy. We extract the direct capture contribution from the total cross section and demonstrate that earlier data are inconsistent with our results.

Resonance strength in {sup 22}Ne(p,gamma){sup 23}Na from depth profiling in aluminum

A novel method for extracting absolute resonance strengths has been investigated. By implanting

Thermonuclear reaction rate of 23mg(p,gamma)24al

^{22}mathrm{Ne}

Thermonuclear reaction rate of {sup 23}Mg(p,{gamma}){sup 24}Al

ions into a thick aluminum backing and simultaneously measuring the