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In 1932 John Douglas Cockcroft and Ernest Thomas Sinton Walton accelerated hydrogen ions from a discharge source through an evacuated tube onto lithium at $45^{\circ }$. A side-facing zinc sulfide screen, viewed by microscope, showed particle scintillations. Mica stopped scattered protons; switching off or blocking the beam removed the flashes. An external screen allowed absorption-range measurements.^[ref]

Magnetic deflection checked voltage calibration. Opposite screens and independent observers found excess coincidences for a thin lithium target, supporting paired alpha particle emission; geometry and screen efficiency limited detection.^[ref]

John Douglas Cockcroft's 1951 lecture recalls detection at $125\mathrm{kV}$ and an absorption range about $8.4\mathrm{cm}$, then refined alpha particle energies about $8.6\mathrm{MeV}$ each. He places the work under Ernest Rutherford's direction. The inferred nuclear reaction was lithium-7 plus a proton producing two alpha particles.^[ref]

The logic has several independent links. Beam blocking tests whether the flashes depend on bombardment. An absorber tests whether scattered beam particles could reach the screen. A particle range tests product identity and kinetic energy, while coincidences test whether two products belong to one event. These tests support a reaction interpretation jointly; counting flashes alone is not an isotope identification, and a range-to-energy conversion needs calibration. The lithium proton reaction energy below is a modern calculation, separate from those historical measurements.

Ernest Walton and John Cockcroft produced nuclear reactions with a controlled beam of electrically accelerated protons. Their 1932 lithium experiment detected energetic alpha particles from the target. The apparatus made both the incident proton energy and the outgoing reaction products experimentally accessible, replacing reliance on naturally emitted projectiles alone. The result demonstrated how accelerator control could be used to investigate the binding and transformation of atomic nuclei.^[ref]

A physicist.^[ref][ref]

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]