James Chadwick (1891–1974) was the British physicist who found the last big piece of the atomic nucleus — the neutron — and bagged a Nobel Prize for it in 1935. He supposedly signed up for physics at university by mistake (he'd meant to study maths) and was too shy to correct the error. Lucky mistake.
For years physicists were puzzled: atomic nuclei weighed far more than their protons alone
could explain. In 1932 Chadwick ran a clever series of experiments and proved there was a
second nucleus particle — the neutron — with almost the same mass as a proton but no
electric charge. That completed the picture and slotted neatly into the
Chadwick had a rough start. Studying in Germany when the First World War broke out, he spent four years interned in a civilian prison camp — and still tried to do physics there with makeshift equipment. Once free, he found the neutron in a legendary burst of work over just a couple of weeks. That chargeless particle he uncovered turned out to be the key that unlocked nuclear energy, a legacy Chadwick himself viewed with deep unease.