Level structure of18Ne and its importance in the14O(α,p

Abstract

The level structure of 18 Ne above the α-decay threshold has been studied using the 16 O( 3 He,n) reaction. A coincidence measurement of neutrons and charged particles decaying from populated states in 18 Ne has been made. Decay branching ratios were measured for six resonances and used to calculate the 14 O(α,p) 17 F reaction rate which is a measure of one of two breakout paths from the Hot CNO cycle. The new experimental information combined with previous experimental and theoretical information provides a more accurate calculation of the reaction rate.

Examination of the role of theO14(α,p)F17reac

“…6 in Ref. [39]). As discussed above, such a state at E x = 6.85 ± 0.10 MeV was also observed in the present work.…”

“…Because no such state was previously observed in 18 Ne, Notani et al [32] speculated that it might be due to a state at E x ∼ 7.1 MeV decaying to the first excited state of 17 F. Later, a careful 17 F+p scattering experiment [30] was performed, but no evidence of inelastic 17 F+p scattering was observed in this energy region, and the decay branching ratio to the first excited state ( p / p ) was constrained to be <0.03. Almaraz-Calderon et al [39] recently reported a ratio of 0.19 ± 0.08 for the 7.05 MeV state. Later, this large ratio was questioned by Fortune [40] who estimated a ratio less than about 2 × 10 −4 , in agreement with an earlier limit of 1/90 from Harss et al [35].…”

“…Constraining the proton-decay branches to the ground and first excited (E x = 495 keV, J π = 1/2 + ) states of 17 F is therefore of critical importance. Such inelastic channels were observed for several 18 Ne levels [20,29,32,37,39]; however, there are still some controversies [40].…”

“…[20], Bardayan et al [37] derived a new ratio of p / p = 0.42 ± 0.03 and = 53.7 ± 2.0 keV. Most recently, AlmarazCalderon et al [39] populated the 6.15-MeV state via the 16 O( 3 He,n) 18 Ne reaction. Due to large uncertainties, they only estimated the upper limit of this branching ratio ( p / p 0.27).…”

“…It is worth noting that our rates are orders of magnitude greater than those of Refs. [35,39] below 0.3 GK, because they did not consider the interference effects and only utilized a simple narrow-resonance formalism to calculate the resonant rate of the 6.15-MeV state. The comparison between our rates and the previous ones are shown in Fig.…”