The phrase ‘splitting the atom’ is often quoted as a benchmark for scientific discovery.

THE phrase ‘splitting the atom’ is often quoted as a benchmark for scientific discovery.

Indeed, the achievement of physicists John Cockcroft and Ernest Walton was monumental, unlocking the secrets of the atomic nucleus, proving Einstein’s E = mc² and opening the door to nuclear power.

The structure of atoms was established by New Zealander Ernest Rutherford in 1911.

Each has a positively-charged nucleus surrounded by negatively-charged electrons.

The nucleus’s positive charge is due to the presence of tiny particles within it called protons.

Each chemical element has a unique number of protons in the nucleus of each atom.

Every hydrogen nucleus has one, for example; every helium nucleus, two; then lithium, three, beryllium, four, and so on.

Having established that, the next challenge was to delve into the nucleus itself, and try to tear it apart.

Under Rutherford’s guidance at the Cavendish Laboratory at Cambridge University, Cockcroft (1897–1967), from England, and Irishman Walton (1903–1995) built the first particle accelerator in 1932.

With it they achieved the first artificial ‘disintegration’ of the nucleus.

Their machine accelerated protons to high speed so they slammed into a target made of the element lithium. Each lithium atom has three protons in its nucleus.

Whenever an accelerated proton hit a lithium nucleus, the result was a nucleus with four protons: beryllium.

Each newly created beryllium nucleus existed for a fraction of a second, before disintegrating into two fragments (each one a helium nucleus).

These nuclear fragments hit a small phosphorescent screen, producing tiny flashes of light – which told Cockcroft and Walton they had succeeded.

For hours on end the pair had to lie down with their heads inside a wooden box at the foot of the apparatus, staring at the phosphorescent screen and counting the flashes.

The process of a nucleus splitting in two is called fission, so Cockcroft and Walton’s breakthrough was the first example of nuclear fission – although the term is normally reserved for larger nuclei.

When some nuclei break apart, the fragments have less mass than the original nucleus.

And, as predicted in Einstein’s mass-energy equation E = mc2, the ‘missing mass’ (m) is converted into energy (E).

The device Cockroft and Walton used was a ‘linear accelerator’ because it moved protons in a straight line.

In 1929, American physicist Ernest Lawrence (1901–1958) invented the ‘cyclotron’, in which particles travel around a (near) circular enclosure, accelerated by electric fields and magnetic pulses.

Today, most particle accelerators are large, powerful cyclotrons. The biggest is the Large Hadron Collider at the headquarters of the Organisation Européenne pour la Recherche Nucléaire (CERN) in Geneva, Switzerland.

It is an underground ring 27 kilometres (16 miles) in diameter.

Scientists designed it to recreate the conditions in the instant after the Big Bang, hoping to discover the very building blocks of all physical matter.

In 2008, they began using the collider to smash particles together at almost the speed of light, hoping that the resulting debris would include new types of subatomic particles, and specifically one dubbed the Higgs Boson.

It was named after an English Professor, Peter Higgs, who predicted its existence in 1964 and said it could be everywhere in the universe, acting as a "glue" holding all other particles together and giving them mass.

In June 2012, after trawling an enormous amount of computer data generated by the collisions, CERN announced they believed they had found the Higgs. It is one of the historic breakthroughs of modern science.