Rather than accept this rather unpalatable conclusion, Wolfgang Pauli proposed that a third particle named a neutrino, or little neutral particle, is emitted in the decay, thus accounting for the missing energy and angular momentum. The presumed electrical neutrality of the particle explained the difficulty of detecting it. Over 25 years passed before Frederick Reines and Clyde Cowan from Los Alamos observed this elusive particle. The three forms of radioactive decay are associated with three of the four known fundamental forces of nature. Gamma decay is electromagnetic in nature, while alpha decay involves the breaking of bonds produced by the nuclear or strong force.
Beta decay is a manifestation of the so-called weak force.
We now have excellent evidence that protons, neutrons, and many other sub-nuclear particles, are made up of particles called quarks .