= Cockcroft-Walton lithium disintegration experiment
{c}
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.<Experiments with High Velocity Positive Ions. II. The Disintegration of Elements by High Velocity Protons by John Douglas Cockcroft and Ernest Thomas Sinton Walton>[Experiments with High Velocity Positive Ions. II. The Disintegration of Elements by High Velocity Protons, 1932, pp. 230–232, sections 2–3, Fig. 1; primary text inspected in the Scribd transcription]{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.<Experiments with High Velocity Positive Ions. II. The Disintegration of Elements by High Velocity Protons by John Douglas Cockcroft and Ernest Thomas Sinton Walton>[pp. 231, 237–238, section 4, Figs. 5–6: corrected voltage calibration, paired screens and random-coincidence comparison]{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>.<Experiments on the interaction of high-speed nucleons with atomic nuclei by John Douglas Cockcroft>[Experiments on the interaction of high-speed nucleons with atomic nuclei, lecture delivered 11 December 1951, pp. 167–170, Figs. 2–4; primary text inspected in the Scribd transcription]{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.
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