Evidence for O15+α resonance structures in Ne19 via direct measurement

Abstract

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s-wave resonances for the 18F(p,$\alpha$α)15O reaction in novae

“…A later analysis of this same reaction by Parikh et al, including the highest-resolution data, noted that the width of the 6.29 MeV state was broader than the experimental resolution (≈ 10 keV FWHM) and could consist of more than one unresolved state (energies of 6282 and 6295 keV are suggested) or a single broad state with a width of ≈ 16 keV [23]. More recently an R-matrix analysis of resonant states in 19 Ne produced in the 15 state at ∼ 6.28 MeV [44]. Our present data are not compatible with with a pure ΔL = 0 transition populating the 6.29 MeV peak since it increases noticeably in strength at more backward angles, relative to GT transitions.…”

Charged-particle branching ratios above the neutron threshold in F19 : Constraining N15 production in core-collapse supern

“…One main contamination is from the decay of 7 Li into α + 3 H following excitation which is the cause of two of contaminating loci. The other main contaminating channel is the decay of 12 C into 3 α particles via the ground state of 8 Be. The simulations of this locus slightly underpredict the missing energy; the carbon is predominantly from the backing of the target and the α particles have to traverse the entire target to reach the DSSSDs, resulting in a lower kinetic energy detected in the DSSSDs and therefore a mild increase in the missing energy.…”

“…Additional factors may also lead one to conclude that statistical models may be inappropriate for computing the 18 F+n reaction rates: the nucleus 20 Ne is known to be strongly deformed with strong α-cluster structures [6], and these structures persist into the neighbouring 19 Ne and 19 F nuclei [7,8]. This non-statistical clustering behaviour is not well described by statistical models [9].…”

“…(Top left) The experimental coincidence matrix assuming 19 F(p, p ′ ) 19 F(α) 15 N reaction kinematics. (Top right) The simulated coincidence matrix assuming 19 F(p, p ′ ) 19 F(α)15 N reaction kinematics for various different reactions, including (black)19 F with α decays to the ground state of15 N, (red)19 F with α decays to the first-excited Ex = 5.27-MeV state in15 N, (green)12 C decays through the ground state of8 Be and (blue)7 Li decay into α+t. (Bottom left) The experimental coincidence matrix assuming the 19 F(p, p ′ ) 19 F(p)18 O) reaction kinematics.…”

“…However, the level density at the neutron threshold in the compound nucleus 19 F (S n = 10.432 MeV) may not be high enough for statistical models to be used with a great deal of confidence. Additional factors also lead one to conclude that statistical models may be inappropriate for computing the 18 F+n reaction rates: the nucleus 20 Ne is known to be strongly deformed with strong αcluster structures [5], and these structures persist into the neighbouring 19 Ne and 19 F nuclei [6,7]. This nonstatistical clustering behaviour is not well described by statistical models [8].…”