CNO hydrogen burning studied deep underground

Abstract

Abstract. In stars, four hydrogen nuclei are converted into a helium nucleus in two competing nuclear fusion processes, namely the proton-proton chain (p-p chain) and the carbon-nitrogen-oxygen (CNO) cycle. For temperatures above 20 million kelvin, the CNO cycle dominates energy production, and its rate is determined by the slowest process, the 14 N(p, γ) 15 O radiative capture reaction. This reaction proceeds through direct and resonant capture into the ground state and several excited states in 15 O. High energy data for capture into each of these states can be extrapolated to stellar energies using an R-matrix fit. The results from several recent extrapolation studies are discussed. A new experiment at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator in Italy's Gran Sasso laboratory measures the total cross section of the 14 N(p, γ) 15 O reaction with a windowless gas target and a 4π BGO summing detector, down to center of mass energies as low as 70 keV. After reviewing the characteristics of the LUNA facility, the main features of this experiment are discussed, as well as astrophysical scenarios where cross section data in the energy range covered have a direct impact, without any extrapolation. PACS

Short‐lived radioactivity in the early solar system: The Super‐AGB star hypothesis

“…[2001] for a detailed discussion). For the 14 N + p → 15 O + γ reaction, the Doherty models use the rate from NACRE, while the Karakas models use the rate from Bemmerer et al. (2006), which is approximately 30% smaller.…”

“…It mainly affects the final central C ⁄ O ratio and possibly the explosive nucleosynthesis of some intermediate-mass elements forged in the C-burning shell (see Imbriani et al [2001] for a detailed discussion). For the 14 N + p fi 15 O + c reaction, the Doherty models use the rate from NACRE, while the Karakas models use the rate from Bemmerer et al (2006), which is approximately 30% smaller. This rate is the bottleneck of the CNO cycle and has an impact on its energy generation strongly affecting stellar evolution (Imbriani et al 2004) and nucleosynthesis (Palmerini et al 2011).…”

Nuclear Astrophysics with Radioactive Beams

“…Resonant capture reactions on stable and long-lived radioactive targets have been inves-tigated with intense proton and α beams [293,294]. The most recent examples for direct measurements of radiative capture reactions are 23 Na(p, γ) 24 Mg and 17 O(p, γ) 18 F studied at the Laboratory for Experimental Nuclear Astrophysics (LENA) at TUNL [295][296][297] and the 3 He(α,γ) 7 Be [298-300] and 14 N(p, γ) 15 O reactions [301][302][303][304] at the Laboratory Underground Nuclear Astrophysics (LUNA) facility [305,306] located in the Gran Sasso Laboratory.…”