ON THE MEASUREMENT OF THE {sup 13}C(α, n){sup 16}O S-FACTOR AT NEGATIVE ENERGIES AND ITS INFLUENCE ON THE s-PROCESS
- Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, I-95123, Catania (Italy)
- Department of Physics, Florida State University, Tallahassee, FL (United States)
- Cyclotron Institute, Texas A and M University, College Station, TX (United States)
The {sup 13}C(α, n){sup 16}O reaction is the neutron source for the main component of the s-process, responsible for the production of most of the nuclei in the mass range 90 ∼< A ∼< 208. This reaction takes place inside the helium-burning shell of asymptotic giant branch stars, at temperatures ∼< 10{sup 8} K, corresponding to an energy interval where the {sup 13}C(α, n){sup 16}O reaction is effective in the range of 140-230 keV. In this regime, the astrophysical S(E)-factor is dominated by the –3 keV sub-threshold resonance due to the 6.356 MeV level in {sup 17}O, giving rise to a steep increase in the S-factor. Its contribution is still controversial as extrapolations, e.g., through the R-matrix and indirect techniques such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of three or more precisely at astrophysical energies. To provide a more accurate S-factor at these energies, we have applied the Trojan horse method (THM) to the {sup 13}C({sup 6}Li, n {sup 16}O)d quasi-free reaction. The ANC for the 6.356 MeV level has been deduced through the THM as well as the n-partial width, allowing us to attain unprecedented accuracy for the {sup 13}C(α, n){sup 16}O astrophysical factor. A larger ANC for the 6.356 MeV level is measured with respect to the ones in the literature, (C-tilde{sub α{sup 1}{sup 3}C}{sup 17O(1/2+)2} = 7.7 ± 0.3{sub stat} {sub -1.5}{sup +1.}|6 norm fm{sup –1}, yet in agreement with the preliminary result given in our preceding letter, indicating an increase of the {sup 13}C(α, n){sup 16}O reaction rate below about 8 × 10{sup 7} K if compared with the recommended values. At ∼10{sup 8} K, our reaction rate agrees with most of the results in the literature and the accuracy is greatly enhanced thanks to this innovative approach.
- OSTI ID:
- 22270564
- Journal Information:
- Astrophysical Journal, Vol. 777, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Measurement of the {sup 13}C(α,n){sup 16}O reaction with the Trojan horse method: Focus on the sub threshold resonance at −3 keV
Indirect study of the {sup 13}C({alpha},n){sup 16}O reaction via the {sup 13}C({sup 7}Li,t){sup 17}O transfer reaction
Related Subjects
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALPHA REACTIONS
ASTROPHYSICS
ASYMPTOTIC SOLUTIONS
CARBON 13 TARGET
CARBON 17
COMPARATIVE EVALUATIONS
HELIUM BURNING
KEV RANGE
LITHIUM 6 REACTIONS
MEV RANGE
NUCLEOSYNTHESIS
OXYGEN 16
OXYGEN 17
QUASI-FREE REACTIONS
R MATRIX
S PROCESS
STARS