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Lawrence Bragg

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Sir William Lawrence Bragg was a pioneering British X-ray crystallographer.

William Lawrence Bragg
William Lawrence Bragg

He is best known for developing methods to analyze the internal structure of crystals. This work transformed how scientists view the microscopic world. By using X-rays, he helped reveal the arrangement of atoms in solid matter. His contributions were foundational to the field of X-ray crystallography. This science allows us to see the building blocks of both minerals and biological molecules.

Bragg’s most significant discovery involved how X-rays interact with atomic layers. In 1912, while studying at Cambridge, he realized that crystals consist of parallel sheets of atoms. When an X-ray beam strikes these sheets, the rays are deflected by collisions with the atoms. Most of these rays cancel each other out because they are out of phase. However, if the beam hits at a specific angle, the rays become in phase. This happens when the distance between the atomic sheets equals the wavelength of the X-ray. These synchronized rays produce a visible spot on a nearby film. Bragg expressed this relationship through the Bragg equation, which relates wavelength, atomic spacing, and the angle of reflection.

To prove this theory, Bragg worked closely with his father, William Henry Bragg. They built a specialized apparatus to test their ideas. This machine allowed a crystal to be rotated to very precise angles. While rotating the crystal, they could measure the energy of the reflected rays. This setup enabled them to calculate the exact distances between atomic sheets. They used the weight of the crystals and the Avogadro constant to find these spacings. This work allowed them to determine the wavelengths of X-rays produced by different metallic targets. Their partnership was unique, as they shared the 1915 Nobel Prize in Physics.

Bragg's career was marked by both scientific triumph and personal challenge. He was born in Adelaide, South Australia, on March 31, 1890. He moved to England in 1908 when his father accepted a position at the University of Leeds. Bragg studied at the University of Cambridge, where he earned first-class honours in physics in 1911. In 1915, at just 25 years old, he became the youngest Nobel laureate in any science category. This record still stands as of 2025. During World War I, he also served as a second lieutenant and worked on sound ranging technology.

Sound ranging was a vital military application of his physics expertise. Bragg and his team needed to locate enemy artillery by the sound of its firing. The problem was that heavy guns produced booms at frequencies too low for standard microphones. To solve this, his group devised a hot wire air wave detector. This device could detect the subtle air waves caused by the explosions. The British Army adopted this system, and it was later used by American forces as well. For these efforts, Bragg was awarded the Military Cross and became an Officer of the Order of the British Empire.

Later in his career, Bragg served as the director of the Cavendish Laboratory at Cambridge. He reorganized the laboratory into smaller research units. He believed the ideal unit consisted of six to twelve scientists and several assistants. Under his leadership, the laboratory became a hub for major biological discoveries. He supported researchers like Max Perutz, who used X-ray diffraction to study haemoglobin. This research proved that X-rays could decipher the structures of giant biological molecules.

Lawrence Bragg Blue Plaque Manchester
Lawrence Bragg Blue Plaque Manchester

This paved the way for the study of proteins and other complex life structures.

Bragg’s work had a direct connection to the discovery of the structure of DNA. In February 1953, James Watson and Francis Crick reported their findings on the DNA double helix. This discovery was made possible by the field of crystallography that Bragg helped build. He also supported the work of Rosalind Franklin, whose "photograph 51" was essential to identifying the double helix shape. Bragg’s influence extended to the formation of the International Union of Crystallography, where he served as the first president. His legacy remains central to modern chemistry, physics, and molecular biology.

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