 After two years at the Massachusetts Institute of Technology , Bradbury became an assistant professor of physics at Stanford University in 1935 , rising to become an associate professor in 1938 , and a full professor in 1943 . He became an expert on the electrical conductivity of gases , the properties of ions , and the behavior of atmospheric electricity , publishing in journals including the Physical Review , Journal of Applied Physics , Journal of Chemical Physics , and the Journal of Atmospheric Electricity and Terrestrial Magnetism . He invented the Bradbury @-@ Nielsen shutter , a type of electrical ion gate , widely used in mass spectrometry in both time @-@ of @-@ flight mass spectrometers and ion mobility spectrometers . 
