Hannah Bos, of Waimea College, asks :-

How did Rutherford go about splitting the atom?

John Campbell, a physicist at the University of Canterbury and the author of "Rutherford Scientist Supreme" and www.rutherford.org.nz, responded.

Behind many great discoveries is a long history of hard work.

By 1907 Rutherford in Canada was firing alpha particles (ie the nuclei of helium atoms) at gases and thin solids, and showing that some alpha particles were scattered, ie the beam became fuzzy.

After he moved to Manchester in 1907 he had his assistant, Hans Geiger, study this scattering. An undergraduate student, Ernest Marsden, who later came to New Zealand to work, was asked to see if he could detect any alpha particles which had been scattered through very large angles. He discovered that some were scattered backwards. In 1911 Rutherford interpreted these results as showing that the nucleus of an atom was very tiny, about a thousandth the diameter of an atom.

Rutherford then had Marsden play marbles with atoms. He fired alpha particles at materials which were made up of light atoms, eg wax as it has lots of light hydrogen atoms in it. When an alpha particle hit a hydrogen nucleus head on, the light hydrogen nucleus was sent flying, much like a large marble hitting a small one.

Because the nucleus is so small only about one in every ten thousand alpha particles struck a hydrogen nucleus head-on.

In 1917, late in the First World War, Rutherford was sufficiently free of war work to be able to go back to these experiments. He fired alpha particles at different gases. With nitrogen gas he found hydrogen nuclei being ejected with energies that were far higher than the energy of the incoming alpha particle. So these weren't nuclei from hydrogen atoms but a hydrogen nucleus from inside the nitrogen nucleus. He had split the nucleus.

In inducing this nuclear reaction Rutherford was not only the first person to split the atom, but also the world's first successful alchemist.

That nuclear reaction is shown on the 1971 New Zealand 7c postal stamp. He didn't publish his conclusion until 1919. That is why the $1.10 New Zealand Rutherford postal stamp of 1999 is labelled "SPLITTING THE ATOM" but is dated 1919, rather than when he did the work. Curiously, the illustration used, a nuclear atom, is not associated with the splitting of the atom.