Sir William Lawrence Bragg (31 March 1890 – 1 July 1971) was an Australian-born British X-ray crystallographer who uniquely shared a Nobel Prize with his father William Henry Bragg – the 1915 Nobel Prize in Physics "for their services in the analysis of crystal structure by means of X-rays", an important step in the development of X-ray crystallography. As of 2025, Bragg is the youngest ever Nobel laureate in physics, or in any science category, having received the award at the age of 25. Bragg was the director of the Cavendish Laboratory, Cambridge, when James D. Watson and Francis Crick reported the discovery of the structure of DNA in February 1953.
Education William Lawrence Bragg was born on 31 March 1890 in Adelaide, South Australia, the son of William Henry Bragg (1862–1942), who was appointed Elder Professor of Mathematics and Physics at the University of Adelaide in 1885, and Gwendoline Todd (1869–1929), daughter of Charles Todd, government astronomer of South Australia. In 1900, Bragg enrolled at Queen's School, North Adelaide, followed by five years at St Peter's College, Adelaide. He went to the University of Adelaide at the age of 16 to study mathematics, chemistry, and physics, graduating in 1908. The same year, his father accepted the Cavendish Chair of Physics at the University of Leeds and brought the family to England. Bragg enrolled at the University of Cambridge as an undergraduate student of Trinity College, Cambridge, in the autumn of 1909, receiving a major scholarship in mathematics, despite taking the exam while in bed with pneumonia. After initially excelling in mathematics, he transferred to the physics course in the later years of his studies, and graduated in 1912 with First Class Honours in the Natural Sciences Tripos. In 1914, Bragg became a Fellow and Lecturer in Natural Sciences at Trinity College. Among Bragg's other interests was shell collecting; his personal collection amounted to specimens from some 500 species; all personally collected from South Australia. He discovered a new species of cuttlefish – Sepia braggi, named for him by Joseph Verco.
Career and research
X-rays and the Bragg equation In 1912, as a first-year research student at Cambridge, W. L. Bragg, while strolling by the river, had the insight that crystals made from parallel sheets of atoms would not diffract X-ray beams that struck their surface at most angles because X-rays deflected by collisions with atoms would be out of phase, cancelling one another out. However, when the X-ray beam struck at an angle at which the distances it passed between atomic sheets in the crystal equalled the X-ray's wavelength then those deflected would be in phase and produce a spot on a nearby film. From this insight he wrote the simple Bragg equation that relates the wavelength of the X-ray and the distance between atomic sheets in a simple crystal to the angles at which an impinging X-ray beam would be reflected. His father built an apparatus in which a crystal could be rotated to precise angles while measuring the energy of reflections. This enabled father and son to measure the distances between the atomic sheets in a number of simple crystals. They calculated the spacing of the atoms from the weight of the crystal and the Avogadro constant, which enabled them to measure the wavelengths of the X-rays produced by different metallic targets in the X-ray tubes. W. H. Bragg reported their results at meetings and in a paper, giving credit to "his son" (unnamed) for the equation, but not as a co-author, which gave his son "some heartaches", which he never overcame.
Work on sound ranging Bragg was commissioned early in World War I in the Royal Horse Artillery as a second lieutenant of the Leicestershire battery. In 1915 he was seconded to the Royal Engineers to develop a method to localise enemy artillery from the boom of their firing. On 2 September 1915 his brother was killed during the Gallipoli Campaign. Shortly afterwards, he and his father were awarded the Nobel Prize in Physics. He was 25 years old and remains the youngest science laureate. The problem with sound ranging was that the heavy guns boomed at too low a frequency to be detected by a microphone. After months of frustrating failure he and his group devised a hot wire air wave detector that solved the problem. In this work he was aided by Charles Galton Darwin, William Sansome Tucker, Harold Roper Robinson, Edward Andrade and Henry Harold Hemming. British sound ranging was very effective; there was a unit in every British Army and their system was adopted by the Americans when they entered the war. For his work during the war, he was awarded the Military Cross and appointed an Officer of the Order of the British Empire (OBE). He was also mentioned in dispatches on 16 June 1916, 4 January 1917 and 7 July 1919. Hot wire sound ranging was used in World War II during which he served as a civilian adviser. Between the wars, from 1919 to 1937, he worked at the Victoria University of Manchester as Langworthy Professor of Physics. He became the director of the National Physical Laboratory in Teddington in 1937. After World War II, Bragg returned to Cambridge, splitting the Cavendish Laboratory into research groups. He believed that "the ideal research unit is one of six to twelve scientists and a few assistants".
University of Manchester
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