A slow neutron, with almost no kinetic energy, is taken in by lithium-6…

Step 1. The Q value. Before: $6.015123\ \text{u} + 1.008665\ \text{u} = 7.023788$ u. After: $4.002603\ \text{u} + 3.016049\ \text{u} = 7.018652$ u. The loss is $0.005136$ u, so $Q = 0.005136\ \text{u} \times 931.494\ \text{MeV/u} = 4.784$ MeV.

Step 2. The sharing. The triton ($3.016049$ u) is lighter than the alpha particle ($4.002603$ u), so the triton takes the larger share. $K_T = Q\,\dfrac{m_\alpha}{m_\alpha + m_T} = 4.784\ \text{MeV} \times \dfrac{4.002603}{7.018652} = 2.728$ MeV. The alpha particle has $K_\alpha = 4.784\ \text{MeV} - 2.728\ \text{MeV} = 2.056$ MeV.

Why a slow neutron is enough. The reaction is exothermic, and the neutron has no charge, so there is no electric barrier to climb. A proton would have to overcome the repulsion of the three protons of lithium. This is why tritium for a fusion plant is made in a blanket of lithium by neutrons.