Proton pickup by α-particles to unbound states☆

Abstract Two conspicious peaks are observed in the two-dimensional coincidence spectra of α-particles and protons emitted in bombardments of 40 Ca, 90 Zr and 208 Pb with 96.8 MeV α-particles. On the basis of kinematics these peaks are identified as the breakup products of 5 Li formed in the (α, 5 Li(g.s)). reaction. A clustering of events in the 40 Ca and 90 Zr spectra at lower α-particle and proton energies is identified as coming from the decay products of 6 Be ∗ (1.67 MeV)2 + state formed in the (α, 6 Be ∗ (1.67 MeV)) reaction. The differential cross section for the (α, 5 Li(g.s)) reaction is deduced at 17°, 23° and 35° in the c.m. system for 40 Ca and at 23° for 90 Zr and 208 Pb. It is found that distorted-wave Born approximation calculations reproduce the slope but not the absolute magnitude of the differential cross sections. The magnitude of the (α, 5 Li(g.s.)) differential cross section at 23° is about 2 mb/sr for all three nuclei studied. These differential cross sections are compared to those for the (α, 5 He(g.s.)) reaction. It is concluded that most of the strength of a plateau-like structure seen in the spectra of inelastically scattered α-particles comes from thedecay α of 5 He(g.s.) rather than 5 Li(g.s.).