Cockcroft and Walton Experiment

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This experiment by John Cockcroft and Ernest Walton is generally seen as the first confirmation of Albert Einstein's famous formula E=mc².[1]

Conducted in April 1932 at the University of Cambridge's Cavendish Laboratory in England, the physicists Cockroft and Walton successfully split lithium atom nuclei by colliding them with artificially accelerated protons. This experiment is general hailed as being the first transmutation of an element using artificially accelerated particles, for which they were honored with the Nobel Prize in 1951.[2]

Critics maintain that such verification is impossible, due to a misunderstanding about the nature of the universe.

Cockcroft and Walton "did not see their experiments as a test of Einstein's mass-energy relationship; rather, they simply used that relationship in their analysis, assuming it to be valid "[3] The first to stress this aspect of the experiment was the eminent physicist Kenneth Bainbridge in 1933:

The gain in energy in the reaction is 16.97×106 e-volts, an energy equivalent to 0.0182 mass units on the O16 scale if ΔE =C²Δm. Taking Aston's values for the mass of helium and hydrogen and the author's value, 7.0146±0.0006 for Li7, the mass change is 0.0181 ± 0.0006 in the reaction which may be represented as Li7 + p → 2α. Within the probable error of the measurements the equivalence of mass and energy is satisfied. --Kenneth Bainbridge

Neither the Nobel Prize committee nor the prize recipients made the claim that their experiment verified of Albert Einstein's famous E=mc² formula.[4][5]


  1. Mike Poole Cockcroft's subatomic legacy: splitting the atom, Cern Courier, Nov 20, 2007
  2. The Nobel Prize in Physics 1951,, 23 Jan 2013
  3. Roger H. Stuewer: Mass-Energy in Einstein in Context, Cambridge University Press
  4. The Center for History of Physics: Einstein: Image and Impact, © 1996-2004 - American Institute of Physics
  5. Louise Boylan: Cockroft and Walton Experiment: Converting Mass into Energy