The17 O(p,γ) 18 F reaction plays a important role in hydrogen burning nucleosynthesis. Conflicting values for the low-energy behavior of its cross section exist in the literature. We present direct measurements of the astrophysical S factor of the 17 O(p,γ) 18 F reaction at center-of-mass energies between 250 and 500 keV. These measurements were conducted in inverse kinematics at the DRAGON recoil separator. 26.50.+x,98.80.Ft,24.50.+g,25.40.Lw

The total cross section of the 12 C+ 16 O fusion reaction has been measured at low energies to investigate the role of this reaction during late stellar evolution burning phases. A high-intensity oxygen beam, produced by the 5MV pelletron accelerator at the University of Notre Dame, impinged on a thick, ultra-pure graphite target. Protons and γ-rays were simultaneously measured in the center-of-mass energy range from 3.64 to 5.01 MeV for singles and from 3.73 to 4.84 MeV for coincidence events, using silicon and Ge detectors. Statistical model calculations were employed to interpret the experimental results. The emergence of a new resonance like broad structure and a decreasing trend in the S-factor data towards lower energies (opposite to previous data) are found for the 12 C+ 16 O fusion reaction. Based on these results the uncertainty range of the reaction rate within the temperature range of late stellar burning environments is being discussed .

Background: Discrepancies exist between the observed abundances of argon and calcium in oxygen-neon nova ejecta and those predicted by nova models. An improved characterization of the 38 K(p, γ) 39 Ca reaction rate over the nova temperature regime (∼ 0.1-0.4 GK), and thus the nuclear structure of 39 Ca above the proton threshold (5770.92(63) keV), is necessary to resolve these contradictions. Purpose: The present study was performed to search for low-spin proton resonances in the 38 K + p system, and to improve the uncertainties in energies of the known astrophysically significant proton resonances in 39 Ca. Method: The level structure of 39 Ca was investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the 40 Ca(3 He, α) 39 Ca reaction. Differential cross sections were measured over 6 laboratory angles at 21 MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of observed levels with special attention to those significant in determination of the 38 K(p, γ) 39 Ca reaction rate over the nova temperature regime. Results: The resonance energies corresponding to two out of three astrophysically important states at 6154(5) and 6472.2(24) keV are measured with better precision than previous charged-particle spectroscopy measurements. A tentatively new state is discovered at 5908(3) keV. The spinparity assignments of a few of the astrophysically important resonances are determined. Conclusions: The present 38 K(p, γ) 39 Ca upper limit thermonuclear reaction rate at 0.1-0.4 GK is higher than that determined in [Physical Review C 97 (2018) 025802] by at most a factor of 1.4 at 0.1 GK.

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