128 



BELL SYSTEM TECHNICAL JOURNAL 



to use air (or some other gas) of adjustable density; when the scintilla- 

 tion-method is employed, the gas may fill the entire space between 

 the source of the fragments and the fluorescent screen; with other 

 methods of detecting the fragments, it must be contained in a cell 

 which the stream enters and leaves through windows of mica or 

 similar substance. 



G 4.5 



i 3.5 



i'3.0 



' / I 



\ • / 1 



• ^ ,< I 



• 1 



-— ^ ~ i ■! —* 



0.5 0.6 0.7 0.8 



0.9 1.0 I.I 1.2 1.3 1.4 1.5 1.6 



AIR EQUIVALENT IN CENTIMETERS 



Fig. 10 — Ionization produced in a shallow chamber by the least penetrating 

 fragments from the transmutation of lithium by protons. (Oliphant Kinsey & ' 

 Rutherford) 



There is an interesting and important way of confirming the steps 

 in an integral curve such as those of Figs. 8 and 9. Near the rise of ^ 

 such a step, the thickness of the intercepting matter is such that many 

 particles are approaching the ends of their ranges when they emerge] 

 from the last of the screens. Suppose that this last screen is adjoined 

 by a very thin ionization-chamber, like that with which the curve 



