Physics
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt.......108s&link_type=abstract
Thesis (PH.D.)--YALE UNIVERSITY, 1990.Source: Dissertation Abstracts International, Volume: 52-03, Section: B, page: 1514.
Physics
3
Carbon-Nitrogen-Oxygen
Scientific paper
At the high temperatures characteristic of explosive hydrogen burning in red giants and in novae and supernovae explosions, the stellar 13 N(p,gamma) ^ {14}O reaction rate exceeds the 13N(beta^+ nu)13C rate, causing the conversion of the stellar Carbon-Nitrogen -Oxygen (CNO) cycle to the Hot CNO cycle, ^ {12}C(p,gamma)^{13 }N(p,gamma)14 O(beta^ +nu)^ {14}N(p,gamma)^{15 }Obeta^ +nu)^ {15}N(p,alpha)^{12 }C. This substantially increases the nuclear energy production rate over the CNO cycle, and can increase the 15N/^ {14}N abundance ratio to levels consistent with the solar system ratio. The temperature dependence of the stellar 13N(p, gamma)14 O reaction rate must be determined order to better understand the energy generation and ^{15 }N/14N abundance ratio for explosive hydrogen burning sites. At nova temperatures, the 13N(p, gamma)14 O resonant reaction rate depends solely on the properties of the low energy (E_{rm c.m. } = 540 keV, E_{rm x} = 5.169 MeV) s-wave resonance in 14O. The ^1 H(14N, 14O)n gamma and 14N(p,n) 14O_{0,1 } reactions have been used to populate this resonance in 14O and measure the gamma branching ratio Gamma_ gamma/Gamma, allowing an indirect determination of the stellar ^ {13}N(p,gamma) 14O reaction rate to be made. At even higher temperatures, the reaction sequence 15O(alpha ,gamma) ^{19 }Ne(p,gamma) 20Na initiates a sequence of rapid proton captures and beta decays, known as the rp process, which can increase nuclear energy generation by a factor of 100 over the HCNO cycle. This reaction sequence also processes CNO seed nuclei out of the HCNO cycle, forming elements with mass >20. This formation of heavier elements during explosive hydrogen burning may explain the recently observed overabundances of Ne, Na, Mg, and Al isotopes in nova ejecta. To better determine the conditions for such breakouts, a high-precision measurement of the ^{20 }Ne(^3He,t) 20Na reaction has been made using 20Ne implanted transmission targets to populate states which may serve as low-energy resonances in the ^{19 }Ne(p,gamma) 20Na reaction. Excitation energies and upper limits on total widths have been determined for four resonances above the 2.199 MeV proton threshold in 20Na, allowing the stellar 19Ne(p, gamma) 20Na reaction rate to be determined at nova temperatures. When combined with a recent study of the ^{15 }O(alpha,gamma ) 19Ne reaction, a better estimate can be made of the conditions for breakout from the HCNO cycle to the rp process.
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