Reaction rates of the s-process neutron sources Ne-22(alpha, n)Mg-25 and C-13(alpha, n)O-16

Drotleff, H. W.; Denker, A.; Knee, H.; Soiné, M.; Wolf, G.; Hammer, J. W.; Greife, U.; Rolfs, C.; Trautvetter, H. P.

doi:10.1086/173119

Cited by 171 publications

(263 citation statements)

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“…During TPs the star expands and cools and the H-burning shell is inactive. While He burning proceeds from the convective to the radiative regime, and eventually switches 1967; Davids 1968;Bair & Haas 1973;Kellogg et al 1989;Drotleff et al 1993;Brune et al 1993;Harissopulos et al 2005;Heil et al 2008). These measurements have been performed at energies down to 270 keV, whereas the Gamow window is at 190 ± 40 keV, corresponding to a temperature of 100 MK.…”

Section: Introductionmentioning

confidence: 99%

NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

Lugaro

Buntain

et al. 2012

ApJ

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We present a new measurement of the α-spectroscopic factor (S α ) and the asymptotic normalization coefficient for the 6.356 MeV 1/2 + subthreshold state of 17 O through the 13 C( 11 B, 7 Li) 17 O transfer reaction and we determine the α-width of this state. This is believed to have a strong effect on the rate of the 13 C(α, n) 16 O reaction, the main neutron source for slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the 13 C(α, n) 16 O reaction. At a temperature of 100 MK, our rate is roughly two times larger than that by Caughlan & Fowler and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected s-process elements and isotopic ratios. There are no changes in the final results using the different rates for the 13 C(α, n) 16 O reaction when the 13 C burns completely in radiative conditions. When the 13 C burns in convective conditions, as in stars of initial mass lower than ∼2 M and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available.

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Section: Introductionmentioning

confidence: 99%

NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

Lugaro

Buntain

et al. 2012

ApJ

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“…In the THM approach, the astrophysical factor of the 13 C(α, n) 16 O reaction is obtained by extracting the quasi-free (QF) contribution to the 13 C( 6 Li, n 16 O) 2 H process. In QF kinematics, 6 Li, characterized by a prominent α ⊕ d cluster structure, is used to transfer the participant cluster α and feed the excited states of 17 O, while the other constituent cluster d is emitted without interacting with 17 O, thus behaving as a spectator to the 13 C(α, n) 16 O sub-process. The 13 C( 6 Li, n 16 O) 2 H reaction was measured at he Florida State University Tandem-LINAC facility, which delivered a E b = 7.82 MeV, 1 mm spot 6 Li beam impinging onto 99% 13 C enriched foils, whose thicknesses were 53 μg/cm 2 and 107 μg/cm 2 .…”

Section: Indirect Measurement Through the Trojan Horse Methodsmentioning

confidence: 99%

“…Furthermore, at such low energies atomic electrons shield nuclear charges determining an enhancement of the S(E)- 2.7 microscopic cluster approach [10] 5.3 microscopic cluster approach [11] 6.3 R-matrix [12] 1.2 ANC [13] 3.4 Spectroscopic factor [14] 2.5 Spectroscopic factor factor right at astrophysical energies [5]. Electron screening determines an exponential increase of S(E) as large as 20% at the lowest energy measured [6]. Indirect measurements deduced the spectroscopic factor or the asymptotic normalization coefficient (ANC) [7] of the 6.356 MeV level, as these parameters fix the resonance top value, allowing for the calculation of the S(E)-factor beyond the energy region explored by means of direct measurements.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the 13C(α,n)16O reaction with the Trojan horse method: Focus on the sub threshold resonance at −3 keV

Cognata¹,

Spitaleri²,

Trippella³

et al. 2014

AIP Conference Proceedings

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Abstract. The 13 C(α, n) 16 O reaction is the neutron source of the main component of the s-process. The astrophysical S(E)-factor is dominated by the -3 keV sub-threshold resonance due to the 6.356 MeV level in 17 O. Its contribution is still controversial as extrapolations, e.g., through R-matrix calculations, and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. Therefore, we have applied the Trojan Horse Method (THM) to the 13 C( 6 Li, n 16 O)d reaction to measure its contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the THM, allowing to attain an unprecedented accuracy. Though a larger ANC for the 6.356 MeV level is measured, our experimental S(E) factor agrees with the most recent extrapolation in the literature in the 140-230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach, merging together two well establish indirect techniques, namely, the THM and the ANC.

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“…Furthermore, at such low energies atomic electrons shield nuclear charges resulting in an enhancement of the S (E)-factor right at astrophysical energies [8]. Since electron screening modifies the low-energy trend of S (E) by a factor of less than 1.2 below 300 keV [11], systematic errors might be introduced by the extrapolation procedure if electron screening is not properly accounted for. In fact, the experimentally observed electron screening enhancement of the cross section turns out to be systematically larger than what present-day atomic models predict [10].…”

Section: Introductionmentioning

confidence: 99%

Measurement of sub threshold resonance contributions to fusion reactions: the case of the¹³C(α, n)¹⁶O astrophysical neutron source

Cognata

Spitaleri

Trippella

et al. 2015

EPJ Web of Conferences

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Abstract. The 13 C(α, n) 16 O reaction is the neutron source for the main component of the s-process. It is is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures 10 8 K. In this temperature region, corresponding to an energy interval of 140 − 230 keV, the 13 C(α, n) 16 O cross section is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17 O. Direct measurements could not establish its contribution owing to the Coulomb barrier between interacting nuclei, strongly reducing the cross section at astrophysical energies. Similarly, indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method was applied to the 13 C( 6 Li, n 16 O)d quasi-free reaction to access the low as well as the negative energy region of the 13 C(α, n) 16 O reaction. By using the generalized Rmatrix approach, the asymptotic normalization coefficient (C 17 O(1/2 + ) α 13 C ) 2 of the 6.356 MeV level was deduced. For the first time, the Trojan Horse Method and the asymptotic normalization coefficient were used in synergy. Our indirect approach lead to (C 17 O(1/2 + ) α 13 C ) 2 = 7.7 +1.6 −1.5 fm −1 , slightly larger than the values in the literature, determining a 13 C(α, n) 16 O reaction rate slightly larger than the one in the literature at temperatures lower than 10 8 K, with enhanced accuracy.

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Reaction rates of the s-process neutron sources Ne-22(alpha, n)Mg-25 and C-13(alpha, n)O-16

Cited by 171 publications

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NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

Measurement of the 13C(α,n)16O reaction with the Trojan horse method: Focus on the sub threshold resonance at −3 keV

Measurement of sub threshold resonance contributions to fusion reactions: the case of the¹³C(α, n)¹⁶O astrophysical neutron source

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Reaction rates of the s-process neutron sources Ne-22(alpha, n)Mg-25 and C-13(alpha, n)O-16

Cited by 171 publications

References 0 publications

NEW DETERMINATION OF THE13C(α,n)16O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

NEW DETERMINATION OF THE13C(α,n)16O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

Measurement of the 13C(α,n)16O reaction with the Trojan horse method: Focus on the sub threshold resonance at −3 keV

Measurement of sub threshold resonance contributions to fusion reactions: the case of the13C(α, n)16O astrophysical neutron source

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NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

NEW DETERMINATION OF THE¹³C(α,n)¹⁶O REACTION RATE AND ITS INFLUENCE ON THEs-PROCESS NUCLEOSYNTHESIS IN AGB STARS

Measurement of sub threshold resonance contributions to fusion reactions: the case of the¹³C(α, n)¹⁶O astrophysical neutron source