The sun can be considered to be a rather large fusion reactor, deriving its fuel from hydrogen. In a typical reaction, 4 protons (from hydrogen) are ultimately fused to form a He nucleus. In the rst step of this process, two protons [ionised hydrogen) are fused to form a deuteron: H+H>2H+X+u. (Data: Mass H= 1.3742 x1027 kg, 2H = 3.34353 x1327 kg