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Blackett, Patrick (Maynard Stuart), Baron Blackett

cloud chamber war london

(1897–1974) British physicist: used an improved Wilson cloud chamber to make discoveries using cosmic rays.

Blackett, the son of a stockbroker, was educated at Osborne and Dartmouth Naval Colleges and saw action at sea in the battles of the Falkland Islands (1914) and Jutland (1916). He then studied physics at Cambridge and, continuing in research, made the first cloud chamber photographs (1924) of the transmutation of nitrogen into oxygen-17 by bombardment with alpha particles (helium nuclei). He was appointed to professorships in London (1933), Manchester (1937) and finally Imperial College, London (1953). During the Second World War Blackett pioneered the use of operational research to produce economies in military resources, including work on submarine warfare, and also invented a new bomb-sight for aircraft. After the war he was active in public affairs, opposing the growing role of nuclear weapons. He was awarded the Nobel Prize for physics in 1948.

The prize winning work was the construction, with , of a cloud chamber that underwent vapour expansion and took a photograph when two aligned Geiger counters were triggered. Blackett used the apparatus to identify the first positron to be seen following their prediction by ; however while he sought further experimental confirmation discovery of the positron was published first.

Blackett and Occhialini in the next year, 1933, in their studies of cosmic rays found that a high-energy photon can transform into a positron and an electron (pair production) and that the reverse process (pair annihilation) also occurs. Some of their cloud chamber photographs showed showers of positrons and electrons formed in this way. Legend has it that Occhialini raced to Rutherford’s house with the first such image, and in his enthusiasm kissed the maid who opened the door.

After the Second World War, working at Imperial College, London, Blackett studied rock magnetism, finding that the Earth’s history included changes in its magnetic field in accord with theory of continental drift over geological time. He was made a life peer in 1969.

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