NUCLEUS OF THE ATOM — ANDERSON 245 



sufficiently large currents to send more than 2,000,000,000,000,000 

 protons or deutons into the target per second, at speeds in excess of 

 10,000 miles per second. 



Lauritsen and Crane use a 1,000,000-volt power transformer set 

 to speed up their bombarding particles, but two other workers in this 

 country have developed quite ingenious methods to achieve the same 

 end. The first of these, operating in an extremely unique fashion, 

 was developed by E. O. Lawrence and his collaborators at the Uni- 

 versity of California. This method consists essentially of the suc- 

 cessive application, at accurately timed interval^, of relatively low 

 accelerating potentials to the particles, each particle being acceler- 

 ated in many steps until it has attained a high velocity. A radio- 

 frequency oscillator is employed to furnish the timed accelerating 

 pulses; and in one form of their apparatus, the whole accelerating 

 chamber is placed between the pole pieces of a large electromagnet. 

 The action of the magnetic field causing the particles to travel in 

 circles, they thus return at regular intervals to receive another boost 

 by the oscillating electric field until they are taken out for use near 

 the periphery of the accelerating chamber. Through this means 

 particles have been given energies up to some 4,000,000 electron- 

 volts, the highest energy j)articles so far produced by laboratory 

 mean^ and used for atomic disintegrations. 



Another form of apparatus planned to produce particles of still 

 higher energy is now under construction at the Massachusetts Insti- 

 tute of Technology. Designed by Van de Graaff , this device is essen- 

 tially an elaborate modification of the familiar electrostatic ma- 

 chine. It has already produced in preliminary tests potentials of 

 about 7,000,000 volts. The harnessing of potentials of this magni- 

 tude to the speeding up of atomic particles is a technical problem 

 of extreme difficulty. The Massachusetts group has not as yet 

 applied these voltages to atomic transformations. When success- 

 fully harnessed, such voltages will no doubt extend considerably 

 this work in the " chemistry of the nucleus ", in which new elements 

 are built up out of old in a manner much like the building of chemi- 

 cal compounds out of the elements by the chemist. 



Working in Washington, D. C, M. A. Tuve, L. E. Hafstead, and 

 O. Dahl have successfully used for many varied experiments in 

 atomic disintegrations a Van de Graaff generator built on a smaller 

 scale and operating at 2,000,000 volts. 



All cases of nuclear disintegrations so far studied, whether they 

 are stimulated by natural projectiles from radioactive bodies or by 

 the much stronger projectile-beams produced artificially, show pro- 

 nounced differences from the ordinary chemical reactions studied by 

 the chemist. The first difference is that in the nuclear reactions the 



