New constraints on theF18(p,α)O15

Abstract

The degree to which the (p, γ) and (p, α) reactions destroy 18 F at temperatures 1-4×10 8 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18 F, a target of γ-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18 F+p threshold (E x =6.411 MeV in 19 Ne).

Single-nucleon transfer reactions on18F

“…In the calculation of the 18 F(p, α) 15 O reaction rate, the levels at E x = 6419 and 6449 keV (corresponding to resonance energies of E r = 8 and 38 keV respectively) are believed to be relevant. We observed the 6419 keV level but see no evidence of the 6449 keV level in our data.…”

“…While these studies have contributed significantly to our understanding of the situation, there remains considerable uncertainty in the assignment of analog states between 19 F and 19 Ne [12,15]. Many of the observed states in 19 Ne do not have measured spins and parities, but are assigned based on their putative analog states in 19 F. The properties of these unobserved states and precise determination of isospin-mirror symmetry between these two nuclei will influence the 18 F + p reaction rates.…”

“…8 K, the rates of the 18 F(p, α) 15 O and 18 F(p, γ) 19 Ne reactions depend critically on individual 19 Ne resonances around the proton threshold of 6411 keV [1]. Several measurements with different experimental techniques using stable and radioactive beams have been undertaken to search for excited states of 19 Ne and to determine their properties [2][3][4][5][6][7][8][9][10].…”

“…Transfer reactions induced by radioactive beams on deuterium targets are a powerful means for extracting nuclear structure information [15][16][17][18][19]. The spectroscopic information determined from these measurements are the excitation energies and the transferred angular momentum required to populate a given level in 19 Ne and 19 F. The angular distributions were compared to DWBA calculations to extract spectroscopic factors for all the wellpopulated states in the two nuclei.…”

Astrophysically important 19Ne states studied with the 2H(18F, alpha+15O)n Reaction

“…Our present understanding of the energy level structure of 19 Ne is incomplete. According to Bardayan et al [3], Kozub et al [4], and most recently Nesaraja et al [5], there are eight levels in the mirror nucleus 19 F for which analogs have not been seen in 19 Ne above the proton threshold of 6.411 MeV. The properties of these unobserved states may influence the 18 F + p reaction rates.…”