Cyclotron vacuum tank, c 1931.
© Science Museum / Science & Society Picture Library
A cyclotron is an apparatus in which charged atomic and subatomic particles are accelerated by an alternating electrical field, while following an outward spiral or circular path in a magnetic field. The cyclotron was invented by Ernest Orlando Lawrence (1901-1958), an American physicist. The vacuum tank of the cyclotron contains a metal 'dee' (a D-shaped box) at its centre. A charged particle enters the dee and electric voltage is then applied in such a way that the particle accelerates until it leaves the cyclotron.