3He and 4He production by 800 MeV protons from 12C, Ti, and Pb at forward angles

The doubly differential cross section for the production of 3He and 4He by 800 MeV protons from 12C, Ti, and Pb has been measured at laboratory angles of 6 degree and 15 degree. The momentum of the detected helium nuclei varied from 1 to 2 GeV/c, the maximum being well above the incident proton momentum of 1.46 GeV/c. The cross sections were found to increase with increasing target mass and decrease with increasing momentum and scattering angle. In our momentum region, the 3He production cross section is 1.5--10 times larger than 4He depending on the target and the momentum. The data are consistent with the hypothesis that the dominant reaction mechanism is a direct process where the initial nucleon-nucleon scattering is followed by a sequential pickup of neutrons