The oxygen-16 + oxygen-16 reaction

Abstract

The ^(16)O + ^(16)O total reaction cross section was measured at six energies between E_(cm) = 6.80 to 11.85 MeV near the astrophysical region of interest. Angular distributions and cross sections for the production of protons, alphas and deuterons were obtained with counter telescopes in a differentially pumped gas target. No ^3He or ^3H were observed. Cross sections for the formation of ^(31)S and ^(30)p were measured by detecting the betas from their radioactive decays. The angular distribution and cross section for production of neutrons was obtained with a long counter at E_(cm) = 12 MeV, demonstrating that the ^(16)O (^(16)O,pn) process accounts for over 90 % of the ^(30) P formed at this energy. The presence of such three body breakup reactions made the experimental determination of the total cross section difficult. Finally, the ^(16)O + ^(16)O → ^(12)O (g.s.) + ^(20) Ne (g.s.) reaction was studied with a coincidence technique at E_(cm ) = 12 MeV. Gamma spectra were taken at several energies for a number of targets using Ge (Li) counters. Gamma lines from nuclei produced in both two and three body exit channels from ^(16)O + ^(16)O reactions were observed. In addition, the gamma yield as a function of bombarding energy was measured in 50 keV (c .M.) steps for both ^(16)O + ^(16)O and ^(12)C + ^(12)C. The ^(16)O + ^(16)O gamma yield is smoothly varying, indicating that the ^(16)O + ^(16)O reaction cross section does not have large fluctuations with energy similar to the structure seen in ^(12)C + ^(12)C reactions. Nearly all cross sections were measured relative to the ^(16)O + ^(16)O elastic scattering at θ_(lab)= 45° to avoid the problems with direct current integration of heavy ion beams in gas targets. A new, more precise determination of the elastic scattering cross section at θ_(cm) = 90° was made for E_(cm) = 7.3 to 14.4 MeV in steps of 100 keV (C .M.). A previously unknown anomaly was observed near E_(cm) = 10.5 MeV. Elastic scattering cross sections were also obtained for ^(12)C + ^(12)C in steps of 60 keV C.M. energy from E_(cm) = 3.9 to 8.0 MeV at θ_(cm) = 90° In both cases, gas mixtures were used in the differentially pumped system as the target.