144 BELL SYSTEM TECHNICAL JOURNAL 



Th. But their observations were confined to protons of relatively 

 low energy-values, — their upper limit was little over 200,000 electron- 

 volts — and do not prove that faster particles are incapable of trans- 

 mutation. The Berkeley school has already published a number of 

 observations made with protons of energies ranging up to 710,000, 

 and with deutons of energies attaining the unprecedented height of 

 3 MEV; and they find fragments in abundance from a wide diversity 

 of targets. 



Beryllium deserves a special paragraph, since it yields neutrons 

 when bombarded, whether with alpha-particles from radioactive 

 bodies; or with helium ions extracted from a discharge and endowed 

 artificially with energies of 600,000 electron-volts and upward; or with 

 deutons. The first of these processes is the one which led to the 

 discovery of the neutron; the second, which incidentally marks the 

 first employment of artificial alpha-particles (since these helium ions 

 are alpha-particles in all but origin, except for the unimportant 

 difference that each possesses an extra-nuclear electron while it is 

 approaching the target) is a recent achievement of the Pasadena 

 school (Crane, Lauritsen and Soltan) ; the third was achieved both at 

 Pasadena and at Berkeley. These three processes are now in rivalry 

 with one another, and it remains to be seen which will be producing 

 the greatest number of neutrons, a year or five years hence. It is 

 still very doubtful how the third takes place: perhaps the deuton 

 merges with the beryllium nucleus, as in the other cases the alpha- 

 particle is supposed to do (page 155), or perhaps it knocks a pre- 

 existent neutron out of the beryllium structure and goes unaltered on 

 its way. This too is a problem for the future, and one in the solving 

 of which the charged fragments likewise observed will probably play 

 a part. 



The deuton itself is in all probability a complex particle; might it 

 not be shattered in impinging against a nucleus, especially some heavy 

 nucleus? This is the interpretation offered by Lawrence of the fact 

 that in sending streams of deutons against targets of several different 

 kinds, he observed charged fragments which were protons (not alpha- 

 particles !) forming a group having a definite range and a definite 

 energy not depending at all on the substance of the target. With 

 1.2-MEV deutons this characteristic energy of the protons is 3.6 MEV. 

 A singular rule governs this quantity: if the energy of the bombarding 

 particles is increased, that of the protons goes up by just the same 

 amount — deutons of energy (1.2 -f x) MEV evoke protons of energy 

 (3.6 + x) MEV. The rule has been verified for values of x up to 1.8, 

 Such a rule is just what one would expect, were there no other frag- 



