  We study ion acceleration mechanisms in laser-plasma interactions using
neutron spectroscopy. We consider different types of ion-collision mechanisms
in the plasma, which cause the angular anisotropy of the observed neutron
spectra. These include the collisions between an ion in the plasma and an ion
in the target, and the collisions between two ions in the hot plasma. By
analyzing the proton spectra, we suggest that the laser-generated plasma
consists of at least two components, one of which collectively accelerated and
can also produce anisotropy in the angular distribution of fusion neutrons.
