The man who looked inside the atom

The structure of the atom
Everyone now knows the basic atomic structure that Rutherford discovered

"We're celebrating something really important. We're celebrating nothing less than the birth of modern physics."

As eulogies go, Dr Andrew Taylor's opening remarks at a conference to mark the one hundredth anniversary of Ernest Rutherford's description of the atom takes some beating.

More's the pity then that this rousing soliloquy, and the speeches that followed, were heard only by a relatively small audience drawn exclusively from within the physics community. A handful of scientists preaching to the converted.

Rutherford's status within that community has never been in doubt, but the physicist and author Graham Farmelo believes the father of nuclear physics deserves much wider acclaim.

"Rutherford's discovery of the structure of the atom is right up there in 20th century science among the greatest discoveries. Right next to Crick and Watson's description of DNA".

To understand why Rutherford inspires such flights of rhetoric we need to scroll back to the turn of the last century, to a period in which JJ Thomson was discovering the electron, and Henri Becquerel was investigating the properties of radioactivity. A period in which the 'plum pudding' model of the atom held sway.

Ernest Rutherford
Rutherford's discovery was a pivotal moment in modern physics

Working with Hans Geiger and and Ernest Marsden in Manchester, Rutherford (who had already received the Nobel Prize for Chemistry for his work on the transmutation of atoms) devised an experiment that involved bombarding a thin sheet of gold foil with Alpha particles.

Most of the particles passed straight through, but every now and then one was deflected onto a fluorescing plate. It was an astonishing observation, and one that took Rutherford the best part of two years to explain.

As he later recalled, "it was as if a 15-inch naval shell had been fired at a piece of tissue paper and bounced back".

What Rutherford realised was that the mass of an atom could not be evenly spread out - like plums in a pudding - but must be focused at its core. Only a solid, dense nucleus would have the mass to divert an energetic Alpha particle set on a collision course. The resulting paper, The Scattering of Alpha and Beta Particles by Matter and the Structure of the Atom, was published in the Philosophical Magazine a hundred years ago this month.

It was Rutherford's intuitive leap to a new 'planetary' model of the atom - where individual electrons orbit a solid central nucleus - that Graham Farmelo argues was one of the most profound insights of 20th century science.

"He was the first person to see that the atom has this weird structure with almost all its mass concentrated in a tiny core that he called the nucleus. On that fundamental insight we've built the whole edifice of the quantum understanding of the atom".

It's an appreciation of one man's vision that's shared by the nuclear physicist, and key-note speaker at the Rutherford 100 conference, Professor Jim Al-Khalili.

"Although science doesn't really work this way you can always pick those wonderful moments when there's a huge breakthrough. Galileo pointing a telescope up into the sky. Hooke looking down a microscope and drawing a flea. Rutherford describing the structure of the atom is another one of these pivotal moments".

A microscopic-black-hole being produced in the collision of two protons
Modern atom-smashers at Cern have continued Rutherfords work

Exactly why Rutherford's name has failed to make it into the select band of scientists whose achievements transcended their own discipline, propelling them into the public consciousness, remains a mystery. The obvious parallel is with the great theoretical physicist of the early 20th Century, Albert Einstein.

But there is still one avenue for Rutherford to achieve the renown his achievements deserve. The atom smashing experiment he designed gave us the basic structure of the atom. A hundred years on another - admittedly somewhat more powerful atom smashing machine - the Large Hadron Collider stands poised to complete that picture with the discovery of the Higgs boson.

It would be a fitting tribute to a great scientist if the experimental physicists at Cern managed to achieve that in the centenary year of Rutherford's backscattering experiment.

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