The youngest Nobel laureate in physics is Lawrence Bragg. He was awarded the Nobel Prize in Physics 1915 at the age of 25, together with his father, William Henry Bragg, “for their services in the analysis of crystal structure by means of X-rays”. He is still the youngest laureate in any of the science prizes, and the Braggs are still the only parent and child to have shared a Nobel Prize. Lawrence did the prize-winning work when he was only 23.
From Adelaide to Cambridge
Bragg was born on 31 March 1890 in Adelaide, Australia, where his father was a professor of mathematics and physics. When he was 19 the family moved to Britain, and he went to Cambridge. In 1912, as a first-year research student there, he had the insight that made his name, the story goes, while strolling by the river.
Reading a crystal with X-rays
A crystal is made of atoms arranged in regular, parallel sheets. When a beam of X-rays strikes it, every sheet reflects a little of the beam. At most angles the reflections from neighbouring sheets are out of step and cancel one another out, and nothing much comes back.
But the ray reflected from a deeper sheet travels a little further than the one from the sheet above it. At certain angles that extra path is exactly a whole number of wavelengths. Then the reflections line up, crest on crest, and add into a bright spot. That condition is Bragg’s law:
Measure the angles of the bright spots and you can work backwards to the spacing of the atoms. Father and son published the method in 1913, in a paper called “The Reflexion of X-rays by Crystals”. X-ray crystallography became his field for the rest of his life.
A prize in wartime
By the time the prize came, Bragg was in uniform. Early in the First World War he had been commissioned in the Royal Horse Artillery, and in 1915 he was moved to work on sound ranging: finding enemy guns from the boom of their firing. On 2 September 1915 his brother was killed in the Gallipoli campaign. Shortly afterwards, he and his father were awarded the Nobel Prize.
The Short draws the X-rays bouncing off two sheets of atoms and the moment their waves line up.
He was 25, and the record has stood ever since. And that’s how we found out.
