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Their proton accelerator was carefully built in a neglected room in the Cavendish Laboratory. Once again, Walton’s innate resourcefulness was fully utilised as the pioneering pair of scientists relied partially on old car batteries and bits of petrol pumps!
Even with these meagre resources, they somehow managed to build an apparatus capable of developing an accelerating voltage of up to 700,000 volts, used to accelerate protons to colossal velocities.
Finally, despite their challenges, on April 14th 1932, Walton and Cockroft succeeded. They did it. As their proton accelerator bombarded a Lithium target, releasing Alpha particles and energy, they became the first people in history to bring about the transmutation of the nucleus of an atom using artificially accelerated particles.
For the first time ever, man had the ability to change the universes fundamental building block, the atom. Surely this was a peerless feat at the time.
· In the apparatus, protons released from a Hydrogen discharge tube were shot into the accelerating tube.
· These protons were accelerated by the very high voltage, down through a vacuum.
· They hit a Lithium target, which was angled at 45˚ to the incoming proton beam.
The products of the reaction moved out at an angle of 90˚ to the beam, where they struck Zinc sulphide screens which gave off microscopic flashes of light (scintillations).
When they experimentally showed that it was Alpha particles (two protons and two neutrons) released, the reactions equation was;
Lithium (three protons and four neutrons) + Hydrogen (one proton) → Helium (two protons and two neutrons) + Helium (two protons and two neutrons) + Energy
Walton was the first to observe this reaction, using a microscope. When their results were published later that month, its importance was embraced by the world with the respect it deserved. Their work was very important for various reasons.
It was one of the most significant developments in the foundation of the branch of physics involving controlled accelerated particles. Subsequent developments encompass many of the original Walton-Cockcroft principals.
It was the first experimental verification of the equation E = mc², developed by Einstein which shows the relationship mass has with energy.
In this experiment, the sum of the masses of the Alpha particles was less than the total mass of the Lithium and protons used. This means that mass was converted into energy.
· The Walton-Cockcroft accelerator provided many times more high velocity protons than the Alpha particles used by Rutherford to achieve nuclear transmutation from the available radioactive material from naturally occurring sources.
This experiment also verified the new wave mechanics predictions and validated Gamov’s calculations.
For his far reaching contribution to the world of science, Ernest Walton was the worthy recipient of the 1951 Nobel Prize for physics, jointly with John Cockcroft.
Later on, Walton was to lecture from 1934 right up until his retirement in 1974. In 1934, Professor Walton married Freda Wilson.
Their four children, following in Ernest’s footsteps, all have science related jobs. During World War two, Walton was privately asked by James Chadwick (the discoverer of the neutron) to go to the United States and join a gathering of workers for ‘war work’, which turned out to be no less than the Manhattan project!
For his own various reasons, however, he decided not to leave Ireland.
Professor Walton passed away on June 25th 1995, but he is still vividly remembered. He was noted, not only for his experimental genius, but also as an engaging and excellent lecturer who had the ability to captivate his listeners through his presentation of often complex topics in an understandable form. As well as being a shy and modest man, he is said to have had a resilience and unrelenting motivation to abide by his deeply rooted principals. One of the true heroes of science.
My sincerest gratitude firstly to my physics teacher Mr. David King, for translation Mrs. Deirdre O’Neill and my sister Eleanor, and to my parents for everything.