Proton pick-up from 19F, 20Ne and 22Ne

Abstract

Energy spectra and angular distributions of the 3He particles from the (d, 3He) reactions on 19F, 20Ne and 22Ne have been measured at an incident energy of 52 MeV. Excitation energies up to 15 MeV ( 18O), 7 MeV ( 19F) and 9 MeV ( 21F) and pick-up from seven different shell-model orbits have been observed. Several previously unknown negative parity states have been found in 18O. A ( 3 2 , 1 2 ) − level at 4.56 MeV was found in 19F, while the known J = 3 2 level at 3.91 MeV was not observed which suggests a positive parity assignment. The hole state spectrum of 21F resembles closely that of 19F. The spectroscopic factors are compared to the predictions from a simple rotational model and from various effective shell-model calculations. All models describe the positive parity transitions leading to 19, 21F reasonably well, but those leading to 18O are only understood by the inclusion of excited core contributions of 4p-2h character in 18O. The low-lying negative parity states, containing essentially the 1p 1 2 hole strengths, are also nicely described by the weak coupling calculations. Higher excited negative parity states show deviations which are discussed in terms of 2p particle-1p hole admixtures.