CONTEMPORARY ADVANCES IN PHYSICS 399 



Bombardment by alpha- par tides : B, Mg, Al (JoHots, Ellis & Hender- 

 son); Na, P (Frisch) ; negative results with H, Li, Be, C, N, O, F, 

 Na, Ca, Ni, Ag (Joliots). 



Bombardment by deutons: Li, Be, B, N, C, O, F, Na, Mg, Al, Si, 

 P, CI, Ca (Henderson, Livingston & Lawrence, with 3-MEV deutons); 

 Li, Be, B, C, Mg, Al (Crane & Lauritsen, with 0.9-MEV deutons). 



Bombardment by protons: B, C (Crane & Lauritsen); C (Cockcroft, 

 Gilbert & Walton with 0.6-MEV protons); C (?) (Henderson et al., 

 with L5-MEV protons). Negative results by Henderson et al. with 

 L5-MEV protons on all but C among the elements listed above before 

 their names. 



Bombardment by neutrons: F, Na, Mg, Al, Si, P, CI, Ti, V, Cr, Fe, 

 Cu, Zn, As, Se, Br, Zr, Ag, Sb, Te, I, Ba, La, U (Fermi); F, Mg, Al 

 (Dunning and Pegram). 



Other Cases of Transmutation 

 It is not altogether safe to separate cases of "induced radioactivity" 

 from "other cases of transmutation," inasmuch as most of the latter 

 class have been observed under conditions where it was impossible to 

 tell whether or not there was a delay between collision and disruption, 

 and perhaps some of them belong in the former class. Of certain 

 transmutations one may say that if there is such a delay, the law of 

 conservation of momentum must be suspended for the duration 

 thereof, resuming its sway only at the moment of the disruption. 

 Nevertheless I should not wish to affirm that for the processes men- 

 tioned in this section or in the Second Part the delay is always literally 

 zero. 



Early in this year was first achieved, at the Cavendish Laboratory 

 by Oliphant, Shire and Crowther, what had been the aim of many 

 physicists for over a decade : the separation of a metal, normally 

 consisting of more than a single isotope, into films each comprising 

 atoms of practically a single isotope only, and thick enough for physical 

 experiments. This was performed with lithium, and when protons 

 and alternatively deutons were projected against films of Li^ and 

 alternatively Li^, the four resulting sets of observations settled the 

 attributions of the various groups of fragments previously observed 

 when ordinary blocks of lithium had been bombarded. The origin of 

 the two long-range groups of paired alpha-particles described in the 

 Second Part was precisely as had been suspected: they proceed from 

 the interactions: 



iHi + aLi^ = 22He^ + {T, - To); iH^ + ,U' = l^He' + {T, - To), 

 where (Ti — To) stands for the amount of energy transformed in each 



