An apparatus for accelerating electrons in a circular path by magnetic induction.In August 1948, the American Military Government in Germany denied a request by scientists in Göttingen to have Siemens & Halske (now Siemens) build a 30MeV betatron....
Chicago's west side VA was still running an Allis Chalmers betatron for radiation therapy 20 years after the unit was obsolete.
This enables to use betatrons for control of large-size luggage on presence of fissile materials.