David Milne, of Kings High School, asks :-

How did Sir Earnest Rutherford split the atom?

John Campbell, the author of Rutherford - Scientist Supreme and www.rutherford.org.nz, responded.

I notice that you have spelt his first name as it appears in the New Zealand birth register.

Rutherford, became the first person in the world to knowingly split an atom, in 1917. (The millenium postage stamp featuring this event uses the date 1919, the date the work was first widely published, not when it was actually done.) It came about in the way science usually progresses, in studying the unknown for its own sake; it came about unexpectedly, while playing marbles with atoms; and it had a longer history than is normally given to it.

By 1911 Rutherford had discovered the nuclear nature of atoms, through experiments in which high speed alpha particles (the nuclei of helium atoms) were scattered in passing through a gold film. In 1913 he extended this work to scattering by lighter atoms which were gases. He was assisted in some of this work by his assistant, Ernest Marsden, who later became Director of Education in New Zealand. Rutherford had anticipated that when using hydrogen gas, light protons (the nuclei of hydrogen atoms) would be ejected with speeds higher than that which the heavier alpha particle had. (You can observe this yourself if you hit a lighter marble with a heavier one, or hit the jack with a lawn bowling ball, or drop a basketball with a tennis ball on top of it.) Marsden observed these emitted protons but also reported that sometimes a few protons seemed to be emitted with speed higher than could be accounted for by a simple collision. At the end of 1914 Marsden left Manchester for New Zealand.

At that time Rutherford was on a tour of Australia and New Zealand and the First World War started. Hence on his return to Manchester all his time went into war work, developing methods of detecting submarines using sound waves. It was not until late 1917 that Rutherford could return to pure research. As projectiles he used the high speed alpha particles, ejected from radioactive polonium atoms. When these were fired into nitrogen gas an occasional extra long range proton was observed. In this case one of the alpha particles penetrated into the nucleus of the nitrogen atom and made the combination unstable so it split into an oxygen atom and the light nucleus of a hydrogen atom, a proton, which was then ejected at very high speed.

It is usually overlooked that in doing this work Ernest Rutherford became the world's first successful alchemist.