Cockcroft–Walton generator
Cockcroft and Walton achieve accelerator-induced lithium disintegration
View full image ↗ How was this image made?
The creative brief sent to the image model. These are instructions, not a record of what actually happened.
Original prompt & settings (JSON) ↗The signal was not a dial reading. Walton crawled under lethal high-voltage gear to a tiny hut, looked through a microscope, and counted pinpricks of light by eye.
The best-supported date: 14 April 1932, at the Cavendish
On the best-supported reconstruction, at Cambridge's Cavendish Laboratory on 14 April 1932, Ernest Walton directed accelerated protons at a thin lithium target and observed bright scintillations characteristic of alpha particles on a fluorescent screen.
The first successful disintegrations appeared at only about 125 kilovolts, far below the accelerator's intended maximum.
John Cockcroft immediately checked and confirmed the observation, and Ernest Rutherford — who had urged the pair to stop hunting only for gamma rays and look directly for alpha particles — was invited to inspect the screen.
Lithium into two alphas
The reaction converted lithium-7 plus a proton into two helium-4 nuclei. The initially measured alpha range was about 8.4 cm in air; refined measurements gave about 8.6 MeV per particle and roughly 17.2 MeV released in total.
This was the first artificial nuclear disintegration produced with accelerated particles, and it supplied an experimental test of mass–energy equivalence.
Rutherford had already induced transformations using naturally emitted alpha particles; the distinction here was the use of artificially accelerated ones.
Not fission, and not the paper's date
The process was proton-induced transmutation of a light nucleus, not the fission of a heavy nucleus, which was identified in 1938–39.
Cockcroft and Walton quickly performed range and paired-emission checks, dated their first Nature communication 16 April and saw it published on 30 April; neither date is the date of the observation.
A modern reconstruction from Cavendish records and Walton's own later account both give 14 April, while the American Institute of Physics historical exhibit hedges between 13 and 14 April.
Sources
Researched 23 Aug 2026 5 sources 2 audit passes Date disputed
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
Date disputed. Sources disagree about when this happened.
What the sources leave uncertain
- A modern scholarly reconstruction based on Cavendish records places the observation on the morning of April 14, and Walton's own later account also gives April 14. The American Institute of Physics historical exhibit, however, hedges the date as April 13 or 14. The exact day therefore deserves a disputed-date flag even though April 14 is the best-supported date.
- The contemporary Nature letter was dated April 16 and published April 30; neither is the date of the initial observation.