O18(p,d)O17andO18(p,t)O16Reactions by a Polarized Proton Beam

The ($p,d$) and ($p,t$) reactions on ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ have been studied using the 24.4-MeV polarized proton beam of the Saclay cyclotron. Differential cross sections and analyzing powers (asymmetries) have been measured for eight deuteron and seven triton groups. These data are also compared with distorted-wave Born-approximation (DWBA) calculations as a test of their validity for a light nucleus. Some of the deuteron angular distributions are not accounted for by the calculations, and in fact for some transitions the results suggest that two-step processes might be involved. The reliability of the spectroscopic information deduced from the ($p,d$) reaction is thoroughly discussed. In the triton optical potential a spin-orbit term with a well depth of about 4 MeV is necessary in order to fit the ($p,t$) analyzing power data for the transitions with $L=0\mathrm{}$ and $L=1\mathrm{}$. For higher angular momentum transfers acceptable fits are obtained only if a radial cutoff is used. The analysis of the transition to the 8.88-MeV ($J^{\pi }=2\mathrm{}$) state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ indicates that the $d$ state component in the triton wave function may be important for ($p,t$) reactions leading to unnatural-parity states.