Sir William Lawrence Bragg CH OBE MC FRS ( 31 March 1890 â `` 1 July 1971 ) was an Australian-born British physicist and X-ray crystallographer . Sir William Lawrence Bragg CH OBE MC FRS ( 31 March 1890 â `` 1 July 1971 ) was an Australian-born British physicist and X-ray crystallographer , discoverer ( 1912 ) of the Bragg law of X-ray diffraction , which is basic for the determination of crystal structure .