Coincidence studies of the reactions 3He + 2H AND 4He + 2H

The reactions 2H(4He, 4He p)n, 2H(3He, 3He p)n and 2H(3He, 3H p)p were studied at incident helium energies of 18.0 and 24.0 MeV. In the 2H(4He, 4He p)n reaction the 4He and p were detected in coincidence at angles which allow low relative momentum of the proton and neutron in the final state. The singlet p-n final state interaction (FSI) was not observed (limit < 3 % of the triplet FSI), in agreement with the prediction of isospin conservation. In the 2H(3He, 3He p)n reaction the singlet p-n FSI was observed. Analysis of these data for the extraction of the p-n scattering length was performed. In the same reaction, a measurement at quasi-free (neutron spectator) angles showed that the spectator-pole cross-section peak was shifted in energy from the value predicted by the simple knock-out model. This effect was reproduced by adding to the knock-out calculation “Coulomb pushing” between the incident helium nucleus and deuteron. The first and second excited states of 4He were observed at excitation energies (E∗) and widths (Γ) of E∗ = 20.01 ± 0.02 MeV, Γ = 0.12 ± 0.02 MeV and E∗ = 21.36 ± 0.10 MeV, Γ = 2.0 ± 0.2 MeV, respectively. Contributions probably due to higher 4He states were seen in the data. Angular correlation results were compatible with a spin zero assignment to the first excited state of 4He.