172 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



plus one electron. Consequently, they weigh just twice as much as the nuclei 

 of ordinary hydrogen atoms. They are known as deuterons. 



The deuteron's added weight makes it an ideal atomic bullet. And here is 

 how Dr. Lawrence planned to send streams of deuterons crashing into the nuclei 

 of other atoms in a constant, destructive barrage: Inside the cyclotron cham- 

 ber was a heated filament that emitted streams of elec^trons. These particles 

 would collide with the electrons surrounding the nuclei of the hydrogen atoms 

 and in the ensuing mix-up the nuclei and their satellites would become sep- 

 arated. The deuterons would be left free to float around the chamber. 

 Eventually, the magnetic force set up by the cyclotron's magnet would pull 

 them between two metal grids separated by a space across which an alternating 

 electrical current of 10 or 15 thousand volts would be operating. As the 

 deuterons floated into this space, they would receive a heavy shock, and under 

 this stimulus fly off toward the side of the chamber. But the magnetic field 

 would pull them back again in a semicircular path until they again came 

 between the two grids. Again they would be shocked and be sent flying out 

 toward the side. And again the magnet would pull them back to complete one 

 full circle of the chamber and be shocked again. 



At each jolt from the current the deuterons would gather more energy. This 

 meant that they would go flying out from between the grids with constantly 

 increasing force and in constantly widening circles. So you get the picture of 

 the atomic bullets receiving shocks one right after the other from a weak 

 electrical force. Each time the bullets receive a shock their energy is increased 

 and they go on, describing wider and wider circles around the cyclotron 

 chamber. Finally, they circle so widely that they reach a slit in the chamber 

 wall and go flying out into the open air. The whole secret of the thing lies in 

 making sure by means of the magnet that the atomic bullets are forced to 

 come back for successive shocks until their energy is built up to the point where 

 they can force their way to the exit. Dr. Lawrence figured that to bombard 

 any substance with his atomic bullets, all he had to do was clamp this sub- 

 stance over the slit and let the onrushing stream of deuterons crash into it. 

 This then was the theory put to the crucial test in 1934 at the Universiy 

 Radiation Laboratory. Dr. Lawrence threw the switch that sent a high-pow- 

 ered radio transmitter pumping energy into the cyclotron and the first experi- 

 ment with the 85-ton machine had begun. 



Within a short time, physicists were amazed to hear that Lawrence and his 

 cyclotron were not only changing familiar elements like platinum into other 

 elements like iridium and gold, but were actually producing substances never 

 before seen on earth. These were the artificially radioactive elements. Perhaps 

 their character is best explained by illustration. 



One of the experiments performed with the cyclotron involved the bombard- 

 ment of iron atoms with the high-speed deuterons produced by the cyclotron. 

 When the deuterons crashed into them with a force of about 8 million volts, 

 the iron atoms were broken up. Some changed into atoms of cobalt or man- 

 ganese. But others were converted into a new form of iron which, like radium, 

 emitted streams of electrically charged particles. In other words, this new iron 

 was radioactive. Thirty-four different elements were subjected to bombard- 

 ment with the 85-ton cyclotron and all of them underwent a transformation, 

 many turning into radioactive substances. Among the artificial radioactive 

 materials produced by the cyclotron were sodium, phosphorus, iron, and iodine. 

 It was even possible by bombarding bismuth to produce a degenerate form of 

 radiima called Radium E. 



i 



