In 1951, the protein a-helix was discovered by American chemist and biochemist Linus Pauling (1901–1994) using X-ray diffraction; it was used to reveal the double-helix structure of DNA in 1953 by New Zealand-born English physicist and molecular biologist Maurice Wilkins (1916–2004), English molecular biologist Francis Crick (1916–2004), British biophysicist and X-ray crystallographer Rosalind Franklin (1920–1958), and American molecular biologist and geneticist James Watson (1928–). British chemist Dorothy Mary Crowfoot Hodgkin (1901–1994) also used the technique to determine the structure of vitamin B12 in 1956; she is also credited with the development of protein crystallography.