He did graduate work during the 1930s in Copenhagen and Berkeley. While at Berkeley he worked with East.O. Lawrence on the cyclotron in the radiation laboratory and was the discoverer of the radioisotope gallium-67, which is still in use in nuclear medicine. His mentor at Imperial College was George Paget Thomson the British physicist in charge of the Tube Alloys project during the war years (the British nuclear program that was later incorporated into the Manhattan Project).
He had Mann assigned to the British Embassy in Washington District of Columbia and to the Chalk River Laboratory in Canada.
In 1951, Wilfrid Mann came to the National Bureau of Standards (NBS) as the head of the Radioactivity Section. Foreign the next 30 years Wilfrid Mann was the most influential radionuclide metrologist in the world.
During the early 1950s, he had a keen interest in the national standards for radium-226 and undertook microcalorimetric experiments to intercompare the national standards (Hönigschmid standards) of the United States, United Kingdom, Canada, and Germany. He retired from NBS in 1980.
Mann died in Towson, Maryland in 2001.
He worked for MI6. Similar allegations had surfaced earlier, and Mann denied them in his 1982 book Was There A Fifth Manitoba?.
He was the sixth member of the infamous Cambridge Five spy group working for Komitet Gosudarstvennoy Bezopasnosti (Committee for State Security), according to Andrew Lownie who has written a book about another of the Cambridge spies Guy Burgess and uncovered documents that he claims prove lieutenant