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Title: 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

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,more » 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.« less
Authors:
; ; ; ; ; ; ;  [1] ; ; ; ; ;  [2] ;  [3] ;  [4]
  1. Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, I-95123, Catania (Italy)
  2. Department of Physics, Florida State University, Tallahassee, FL (United States)
  3. Cyclotron Institute, Texas A and M University, College Station, TX (United States)
  4. Dipartimento di Fisica e Astronomia, Università di Catania, I-95123 Catania (Italy)
Publication Date:
OSTI Identifier:
22270564
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 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