398 BELL SYSTFM TECHNICAL JOURNAL 



The result of bombarding carbon with deutons might be expected 

 to be the same as that of bombarding boron with alpha-particles, it 

 being natural to assume the reactions: 



,W + 6C12 = ^Ni3 ^ ^^1^ followed by 7N" = ,0' + ic 



The half-period of the delayed disruption has been determined at 

 Pasadena as 10.3 minutes. This does not agree with that observed 

 by the Joliots when alpha-particles are projected against boron. The 

 disagreement is not so welcome as agreement would have been, but 

 does not in the least invalidate the foregoing equations, since it is 

 perfectly conceivable that two different unstable nuclei with different 

 half-periods might both have the atomic number 7 and the mass- 

 number 13. Bombardment of carbon with protons leads to delayed 

 disruptions with the same half-period of about ten minutes, and this 

 is not so easy to understand as it may seem, since the obvious notion 

 that the proton and the C^^ nucleus simply merge into a nucleus N^^ 

 which later on explodes leads into difficulties with the principles of 

 conservation of energy and conservation of momentum. 



As to the way in which the number of observed disruptions varies 

 with the kinetic energy Ko of the impinging particles, there are data 

 relating to the bombardment of aluminium by alpha-particles. The 

 Joliots varied Kq from 5.3 MEV downwards; they report that the 

 number of positive electrons diminishes with falling Ko, becoming 

 imperceptible for boron at about 3 MEV, for Mg and Al at 4 to 4.5 

 MEV. Ellis and Henderson varied Kq from 5.5 upward to 8.3 MEV, 

 by using alpha-particles emitted from other radioactive bodies than 

 polonium; they found the number of orestons steadily increasing with 

 rising Kq, rising in the ratio 15 : 1 as Xo was raised from 5.5 to 7 MEV, 

 and showing signs of approaching a maximum not far beyond Ko 

 = 8.3 MEV. 



The positive electrons emitted in induced radioactivity are fre- 

 quently — perhaps generally — accompanied by high-frequency photons, 

 of which energy-measurements may hereafter show that they are due 

 to the coalescence of positive with negative electrons to form light. 



I close this section by listing the elements which have been observed 

 to display induced radioactivity after bombardment by one or other 

 of the four agents of transmutation, and add those which have been 

 tested without positive results, in order to show the scope of the 

 experiments. In certain cases positive results have been obtained by 

 some observers and not by others, but this may signify simply a weaker 

 bombarding stream or a less sensitive detector in the apparatus of 

 the latter. 



