Lithium-6 has three protons and three neutrons. An alpha particle is a particle with two protons and two neutrons. If Li-6 decays to produce an alpha particle, this results in a net loss of two protons and two neutrons. So the lithium decays to a hydrogen (3 protons down to 1 proton). This also means that the mass number of the Li-6 drops by 4 to give a hydrogen atom with a mass number of 2 (1 proton and 1 neutron). This isotope of hydrogen is called deuterium. The nuclear equation is written below:
Li-6 --> He-4 + H-2
Please note that an alpha particle is denoted in the equation as He-4.