John Douglas Cockcroft (1897–1967)

John Cockcroft and Ernest Walton used accelerated protons to produce the disintegration of lithium in 1932. A high-voltage accelerator supplied the projectile beam, while the energetic alpha particles leaving the target provided the reaction signal. The reaction $p+{}^7\mathrm{Li}\to 2\alpha$ releases nuclear binding energy, so the outgoing particles can carry far more kinetic energy than the incident proton. This connected a controlled electrical accelerator with a quantitative nuclear reaction.^[ref]

A physicist.^[ref][ref]