John Turton Randall

Sir John Turton Randall, (23 March 1905 – 16 June 1984) was an English physicist and biophysicist, credited with radical improvement of the cavity magnetron, an essential component of centimetric wavelength radar, which was one of the keys to the Allied victory in the Second World War. It is also the key component of microwave ovens.

Randall collaborated with Harry Boot, and they produced a valve that could spit out pulses of microwave radio energy on a wavelength of 10 cm.

Randall also led the King's College, London team which worked on the structure of DNA. Randall's deputy, Professor Maurice Wilkins, shared the 1962 Nobel Prize for Physiology or Medicine with James Watson and Francis Crick of the Cavendish Laboratory at the University of Cambridge for the determination of the structure of DNA. His other staff included Rosalind Franklin, Raymond Gosling, Alex Stokes and Herbert Wilson, all involved in research on DNA.

Education and early life John Randall was born on 23 March 1905 at Newton-le-Willows, Lancashire, the only son and the first of the three children of Sidney Randall, nurseryman and seedsman, and his wife, Hannah Cawley, daughter of John Turton, colliery manager in the area.

The Magnetron

When the war began in 1939, Oliphant was approached by the Admiralty about the possibility of building a radio source that operated at microwave frequencies. Such a system would allow a radar using it to see small objects like the periscopes of submerged U-boats. The Air Ministry radar researchers at Bawdsey Manor on the Suffolk coast had also expressed an interest in a 10 cm system, as this would greatly reduce the size of the transmission antennas, making them much easier to fit in the nose of aircraft, as opposed to being mounted on the wings and fuselage as in their current systems.

Oliphant began research using the klystron, a device introduced by Russell and Sigurd Varian between 1937 and 1939, and the only system known to efficiently generate microwaves. Klystrons of the era were very low-power devices, and Oliphant's efforts were primarily directed to greatly increasing their output. If this were successful, it created a secondary problem; the klystron was an amplifier only, so a low-power source signal was needed for it to amplify. Oliphant put Randall and Harry Boot on this issue of producing a microwave oscillator, asking them to explore miniature Barkhausen–Kurz tubes for this role, a design already used for UHF systems. Their work quickly demonstrated that these offered no improvement in the microwave range. The klystron effort soon plateaued with a device that could generate about 400 watts of microwave power, enough for testing purposes, but far short of the multi-kilowatt systems that would be required for a practical radar system.

Randall and Boot, given no other projects to work on, began considering solutions to this problem in November 1939. The only other microwave device known at that time was the split-anode magnetron, a device capable of generating small amounts of power, but with low efficiency and generally lower output than the klystron. However, they noted that it had one enormous advantage over the klystron; the klystron's signal is encoded in a stream of electrons provided by an electron gun, and it was the current capability of the gun that defined how much power the device could ultimately handle. In contrast, the magnetron used a conventional hot filament cathode, a system that was widely used in radio systems producing hundreds of kilowatts. This seemed to offer a much more likely path to higher power.

King's College, London In 1946, Randall was appointed Head of Physics Department at King's College in London. He then moved to the Wheatstone chair of physics at King's College, London, where the Medical Research Council set up the Biophysics Research Unit with Randall as the director (now known as Randall Centre for Cell and Molecular Biophysics) at King's College. During his term as Director the experimental work leading to the discovery of the structure of DNA was made there by Rosalind Franklin, Raymond Gosling, Maurice Wilkins, Alex Stokes and Herbert R. Wilson. He assigned Raymond Gosling as a PhD student to Franklin to work on DNA structure by X-ray diffraction. According to Raymond Gosling, the role of John Randall in the pursuit of the double helix cannot be overstated. Gosling felt so strongly on this subject that he wrote to The Times in 2013 during the sixtieth anniversary celebrations. Randall firmly believed that DNA held the genetic code and assembled a multi-disciplinary team to help prove it. It was Randall who pointed out that since DNA was largely carbon, nitrogen and oxygen, it was just the same as the atoms in the air in the camera. The result was a diffuse back-scattering of X-rays, which fogged the film, and so he instructed Gosling to displace all the air with hydrogen. In 1943 he was awarded (with Harry Boot) the Thomas Gray memorial prize of the Royal Society of Arts for the invention of the cavity magnetron. In 1945 he was awarded the Duddell Medal and Prize by the Physical Society of London and shared a payment from the Royal Commission on Awards to Inventors for the magnetron invention. In 1946 he was elected a Fellow of the Royal Society (FRS) and was awarded their Hughes Medal in the same year Further awards (with Boot) for the magnetron work were, in 1958, the John Price Wetherill Medal of the Franklin Institute of the state of Pennsylvania and, in 1959, the John Scott Medal award of the city of Philadelphia. In 1962 he was knighted, and in 1972 he was elected a Fellow of the Royal Society of Edinburgh (FRSE)