Measurement of radiative capture resonance energies with an extended gas target

Outstanding problems in nuclear astrophysics: recent progress at TRIUMF

“…On the other hand, the number of outstanding problems suggests that considerable efforts will be required in the decades to come in order to reach the elusive goal of understanding the origin of the chemical elements and the release of energy in stars and stellar explosions. Some of the most important topics covered here include the cosmological lithium problem, the solar rates of the neutrino producing 3 He(α, γ ) 7 Be and 7 Be(p, γ ) 8 B reactions, the lifetime of the 6.79 MeV state in 15 O for the 14 N(p, γ ) 15 O reaction, and the rates of and sensitivity of X-ray burst models to the hot CNO breakout reactions 15 O(α, γ ) 19 Ne and 18 Ne(α, p) 21 Na.…”

“…In separate measurements it has also now been shown that DRAGON can be used to measure resonance energies to within 0.5% or better. 21 18 F production in classical novae also strongly depends on the thermonuclear rate of 17 O(p, γ ) 18 F, which is part of the hot CNO cycle; the relevant temperature range is between 0.1 and 0.4 GK. The literature on 17 18 F cross section with DRAGON between E rel = 250 and 500 keV.…”

“…31,32 The light nuclei of the hot CNO cycles and the heavier nuclei of the rp process are linked by the breakout reactions 15 O(α, γ ) 19 Ne and 18 Ne(α, p) 21 Na. 33,34 Due to the Coulomb barrier, the latter reaction becomes important at higher temperatures than does the former; hence 15 O(α, γ ) 19 Ne has a larger effect on the hydrogen mass fraction at the time of burst ignition than does 18 Ne(α, p) 21 Na, potentially influencing the dynamics of the burst more strongly. Hence the effect of varying the 15 O(α, γ ) 19 Ne rate in X-ray burst models has been the subject of several investigations.…”

“…Further astrophysical model calculations are required to resolve this apparent discrepancy between different sensitivity studies concerning the importance of the 15 O(α,γ ) 19 Ne reaction in models of Type I X-ray bursts. 49 At temperatures exceeding 0.8 GK and densities above 10 5 g cm −3 in Type I X-ray bursts, breakout from the hot CNO cycles is expected to proceed via the 18 Ne(α, p) 21 Na reaction. 34 The cross section for this reaction has not been directly measured in the relevant energy range below 1.5 MeV due to the lack of suitably intense 18 Ne beams.…”

“…34 The cross section for this reaction has not been directly measured in the relevant energy range below 1.5 MeV due to the lack of suitably intense 18 Ne beams. However, a recent effort at the ISAC-II facility of TRIUMF led by the University of Edinburgh group to measure the cross section of the timereversed reaction p( 21 Na,α) 18 Ne has allowed a reliable determination of the 18 Ne(α, p 0 ) 21 Na reaction cross section from 1.2-2.6 MeV. 50 The experimental cross section was found to be up to a factor of two smaller than theoretical predictions based on Hauser-Feshbach calculations, suggesting that the breakout via this reaction occurs at higher temperatures and later times than previously believed.…”