When the atom was split... Science

Cockcroft-Walton's atom splitting experiment

A Cockcroft-Walton generator   | Photo Credit: Wikedia Commons

When two people discover something simultaneously, or within weeks of each other, working independently, you expect both to be rewarded. But if only one of them picks up the Nobel Prize, while the other isn’t given the entire credit, it definitely lends for a story. Yes, I’m referring to the discovery of Vitamin C and the two men behind it that we looked at last week.

This time around, we are going to see how two people worked together to change the course of their chosen field. Better still, both of them were jointly awarded the Nobel Prize in Physics in 1951 “for their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles”. Going over the head? Let's split up and find out…

John Cockcroft was born in 1897 to a family of cotton manufacturers. A varied educational background that included mathematics at Manchester University, electrical engineering at the College of Technology in Manchester and Mathematical Tripos at St John’s College, Cambridge meant that he was one of those few theoreticians who could put together his mathematical and engineering skills. These stints of education were interspersed by the World War I and a period when he served as an apprentice with an electrical company.

Ernest Walton was born in 1903 and was educated in Belfast and Dublin. He excelled in mathematics and science while with Trinity College, Dublin and graduated in 1926 with first class honours in mathematics and experimental science.

Cockcroft and Walton came together while at the Cavendish laboratory under Ernest Rutherford. In 1928, George Gamow showed that particles could tunnel through potential barriers by applying the newly available quantum mechanics. Cockcroft understood the implications of Gamow’s tunnelling theory - that a much lesser energy than earlier thought might be sufficient for a proton to penetrate the nucleus.

By 1929, they had built the Cockcroft-Walton generator, which with a system of capacitors and thermionic rectifiers could reach voltages up to 600,000 volts. It took them three more years but on April 14, 1932, the research duo bombarded a layer of lithium with hydrogen in a discharge tube that had been accelerated using their generator.

The result? The lithium broke into two helium nuclei and shot off in opposite directions - an atom had been split and nuclear transmutation of one element (lithium) to another (helium) had been achieved for the first time under human control.

Cockcroft and Walton also observed a loss in the total mass of the nuclei, while measurements indicated that the total kinetic energy of the helium nuclei were greater than that of the original hydrogen and lithium nuclei. Even though these initial computations had experimental error, it provided evidence of Einstein’s law (E = mc2) and laid the foundations for further scientific work to confirm the equation in detail.

The duo employed the Cockcroft-Walton multiplier for most the of their research that followed, which eventually led to them bagging the Nobel Prize in Physics in 1951. The Cockcroft-Walton circuit is not only still used to supply voltage in large particle accelerators, but is also employed in everyday high voltage electronic devices like photocopiers and x-ray machines.

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Printable version | Sep 5, 2021 1:21:31 PM | https://www.thehindu.com/in-school/sh-science/13isbsatom/article7095392.ece

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