90 



APPLIED RADIOACTIVITY 



1/nth as great to operate n successive times on a charged particle in the 

 form of an ion and impart to it a prescribed amount of energy. 



An ingenious solution to this problem was proposed by E. O. Lawrence, 

 in 1930, in the form of a magnetic resonance accelerator, or cyclotron. 

 This instrument can produce extremely high-speed ions of various sorts 

 by means of relatively small differences of potential applied a large 

 number of consecutive times. 



The Cyclotron . 



The instrument finally adopted by Lawrence and Livingston [1934], 

 and their co-workers, consists of a large, shallow, cylindrical metal 

 vacuum chamber (Fig. 11-15) in which are inserted two insulated semi- 



um chamber 

 60 in. 

 iameter 



Deflection 

 plate 



pressu 



Fig. 11-15. Cyclotron. General view of a 60-in. D-shaped accelerating chamber 

 which is placed between the magnetic pole pieces of the cyclotron. Direction of 

 magnetic field perpendicular to paper. 



With the support of the Rockefeller Foundation a " Giant Cyclotron " is under 

 construction at the University of California. It will contain 4900 tons of steel and 

 copper, will have a 30-ft. vacuum chamber, and is expected to produce a beam of ions 

 of more than 200 million electron volts. 



circular, flat, hollow D-shaped brass electrodes. The vacuum chamber 

 can, for example, be 60 in. in diameter and about 18 in. high. The two 

 electrodes, or " dees," are made of spun copper, and insulated from each 

 other. They clear the vacuum-chamber walls by about 2 in. The 

 vacuum chamber with its flat circular steel ends is supported between 

 the pole pieces of a powerful electromagnet. These pole pieces are also 

 60 in. in diameter. The magnetic field acts in a direction normal to the 

 radial plane of the dees, i.e., perpendicular to the plane of the paper in 

 Fig. 11-15. 



