Measurement of 42 MeV ⁷Li projectile breakup on ²⁰⁸Pb target near grazing incidence

Abstract

Breakup of 42 MeV ⁷Li projectiles in the field of a ²⁰⁸Pb target are studied near the grazing angle. In inclusive breakup measurements, angular distribution of the a and t fragments are found to be rather flat in nature. The α-τ coincidence measurements are carried out with wide angular separations between the detected fragments. The choice of detection angles enables measurement in the same range of fragment relative energies but very different ⁷Li scattering angles. The direct breakup contribution is found to dominate over the sequential breakup for the θ_α > θ_τ set, while the reverse is true when θ_α < θ_τ. Calculations performed in a full quantum mechanical framework reproduce the overall shape of the direct breakup part of the present data and several existing data on ¹⁹⁷Au and ²⁰⁸Pb targets at nearby energies. The sequential breakup is observed only from the decay of the 4.63 MeV (7/2¯) resonant excited state of ⁷Li and its angular distribution does not fully agree with the existing theoretical predictions. Unlike the direct part, the sequential breakup cross section does not decrease with increasing scattering angles. Similar measurements with halo nuclei would be helpful to study their unknown resonant states.