no BELL SYSTEM TECHNICAL JOURNAL 



were justified in the event; for they detected fragments proceeding 

 from targets of lithium bombarded by their protons, with energy- 

 values anywhere from half-a-million down to only seventy thousand 

 electron-volts. 



It would be hard to overstate the joyful surprise of this announce- 

 ment. Transmutation, of some elements at least, was easier by far 

 than had been thought! It would not after all be necessary to fare 

 forth into the unknown, and face at once the problems of applying 

 voltages without precedent; successes which had seemed doubtful at 

 best and assuredly distant were after all to be had by a relatively 

 slight extension of a known technique. All over Europe and America 

 people began making plans for applying these voltages, so much less 

 formidable than those which had previously been thought indispen- 

 sable. Nevertheless the first who confirmed and extended the work 

 of Cockcroft and Walton were those who had aimed from the start 

 at the higher and harder goal : Lawrence and his colleagues at Berkeley. 

 Their work had not been wasted, for they instantly found themselves 

 able to measure the disintegration of lithium by protons all the way 

 up to 710,000 electron-volts; and within four months they had carried 

 the upper limit onward to 1,125,000, and as I write these lines they 

 have just announced that the limit has soared to three millions! 

 From Pasadena also comes word of transmutation achieved by protons, 

 and deutons, and helium nuclei, endowed with energy by voltages 

 ranging downward from nine hundred thousands. 



These are not the only novel results of the last two years and a 

 quarter. The neutron has disclosed itself not only as a product, but 

 as an agent of transmutation, able to alter nuclei which have thus far 

 resisted both the alpha-particles and the protons which have been 

 showered upon them in laboratories. The disintegrations effected by 

 alpha-particles have been studied with ever-increasing minuteness 

 and detail, and are beginning to show that nuclei are structures 

 capable of existing in various normal states and excited states, char- 

 acterized by distinctive energy-values. The emission of alpha- 

 particles from radioactive nuclei has been studied with a new precision, 

 and leads to the same conclusion. The astonishing feats achieved 

 with bombarding particles of lesser energy have not lessened the hope 

 of achieving startling things with particles of greater. ■ 



Cockcroft and Walton, inspired by theory, had built an apparatus 

 for producing half-million-volt protons, and had proved them able to 

 transmute. The proton-streams had not, however, been greater than 

 five microamperes (one microampere or /za = 6.28-10'^ protons per 

 second). Next Oliphant and Rutherford, inspired by that result, 



