Science

The rate of the ¹⁸F(p,g)¹⁹Ne reaction affects the final abundance of the gamma
-ray observable radioisotope ¹⁸F, produced in novae. However, no successful measurement of this reaction exists and the rate used is

calculated from incomplete information on the contributing resonances. Of the two resonances thought to

play a significant role, one has a radiative width estimated from the assumed analogue state in the mirror

nucleus, ¹⁹F. The second does not have an analogue state assignment at all, resulting in an arbitrary

radiative width being assumed. Here, we report the first successful direct measurement of the

¹⁸F(p,g)¹⁹Ne reaction. The strength of the 665 keV resonance (Ex = 7.076 MeV) is found to be over

an order of magnitude weaker than currently assumed in nova models. Reaction rate calculations show

that this resonance therefore plays no significant role in the destruction of ¹⁸F at any astrophysical

energy

The ²⁰Ne(p, γ)²¹Na reaction is the starting point of the NeNa cycle, which is an important process for the production of intermediate mass elements. The E_c.m. = 1113 keV resonance plays an important role in the determination of stellar rates for this reaction since it is used to normalize experimental direct capture yields at lower energies. The commonly accepted strength of this resonance, ωγ = 1.13±0.07 eV, has been misinterpreted as the strength in the center-of-mass frame when it is actually the strength in the laboratory frame. This has motivated a new measurement of the E_c.m. = 1113 keV resonance strength in ²⁰Ne(p, γ)²¹Na using the DRAGON recoil mass spectrometer. The DRAGON result, 0.972 ± 0.11 eV, is in good agreement with the accepted value when both are calculated in the same frame of reference.

Data from a recent ⁹Be(³He,t )⁹B measurement are used to rule out a possible solution to the cosmological lithium problem based on conventional nuclear physics.