150 BELL SYSTEM TECHNICAL JOURNAL 



If the target is very thin (in the sense of the previous paragraph) 

 the curve ought to show a peak for each group. Such curves, by the 

 usage of page 139, may be styled "disintegration functions" (the term 

 "excitation-function" is also used). 



(/) Finally, when the target is thick the mere existence of sharp steps 

 in the integral distribution-in-range curves, may be taken as a sug- 

 gestion of resonahce, since if a group were evoked by alpha-particles 

 of a wide range of energies it would probably have a broad distribution 

 of speeds. But this is not a very strong argument by itself. 



Despite this great variety of ways of testing for resonance, the situa- 

 tion is still confusing and confused. 



Aluminium has been the object of most of the tests, doubtless be- 

 cause it figured in Pose's discovery. He used methods (a) and (c) 

 and found resonance distinctly and even vividly displayed by tlte 

 60-cm. and the 50-cm. group, and not at all by the 25-cm. group. Chad- 

 wick and Constable used {a) and {b), and concluded that there is 

 resonance for six at least of their eight groups, the two members of a 

 pair appearing and disappearing together. (The remaining pair was 

 elicited by alpha-particles of a limited interval of energy- values extend- 

 ing from a lower limit Kh to the highest value of Kq which they had 

 available.) They also used (e) with a very thin sheet of aluminium 

 (air-equivalent 0.8 mm.) and got a curve with two well-defined peaks. 

 But Steudel also had recourse to method (e), and the curve he got 

 swept smoothly upward ; it is true that his target was notably thicker 

 (air-equivalent 5.2 mm.) and yet one would not expect such a thickness 

 to blot out the peaks if they exist. Harder yet to explain away is the 

 evidence of M. de Broglie and Leprince-Ringuet, who made test {d) 

 with sheets of aluminium of air-equivalent 2.5 mm., and observed all 

 three of Pose's groups over a wide range of values of Kq. — As for the 

 other elements: boron and fluorine and magnesium have all been 

 tested by method (a) , and there are strong indications of resonance for 

 all three, strongest for fluorine. Nitrogen has been studied by Pollard 

 with a modification of (e), and he finds that resonance is displayed by 

 the 6-cm. group but not by the stronger and better-known group of 

 longer range. 



Evidently this is a field which yearns for further cultivation, with 

 more powerful sources of transmuting particles to make possible the 

 use of narrower and more homogeneous beams of these, narrower pen- 

 cils of fragments and thinner strata of matter. The discovery of the 

 capacity of protons to transmute has probably diverted from it some of 

 the attention which otherwise it would by now have received, but the 

 lost ground will doubtless be made up in the course of years, after the 



