CONTEMPORARY ADVANCES IN PHYSICS 



93 



Curves obtained in this way are copied in Fig. 8. The peaks are the 

 traces of Hnes (not so many as a photograph would show, for the 

 method in this respect is not so deHcate) rising up not from the zero- 

 level but from a smooth sweeping curve, carried (hypothetically) in 



H^ 1000 eOOO 3000 4000 5000 fcOOO 



Fig. 8. Beta-ray spectra measured with a Faraday chamber 

 (Lower curve for RaC, upper curves for RaB + RaC. After R. W. Gurney.) 



dashes across the base of the peaks. This is the distribution-curve of 

 the electrons forming the continuous spectrum; integrating it, one 

 obtains the total number of these electrons.^* This number has been 

 measured for radium B and radium C by Gurney; it amounts to some- 

 what more than one electron per self-transmuting atom.-^ A much 

 smaller number, had such a one been found, would have rendered 

 untenable the notion that all the nuclear electrons go into the con- 

 tinuous spectrum; the result proves that there is no such obstacle, 

 not at least in these cases. The beta-ray spectrum of radium E con- 

 sists of a single diffuse band; there are no lines. Emeleus counted 

 the emitted electrons and found a value equivalent to 1.1 electrons per 

 self-transmuting atom.^*^ Perhaps then it is a quality of the nuclear 



-8 This statement is not exact. The curves may be transformed into true distribu- 

 tion-curves, resembling them but not identically like them, by processes involving 

 allowances for the geometry of the apparatus. The area under these true curves must 

 then be found by integration, and gives the total charge borne by the electrons, the 

 quotient of which by e is the desired number of electrons. 



=^ R. W. Gurney, Proc. Roy. Soc, A 109, pp. 540-561 (1925). 



30 K. G. Emeleus, Proc. Camb. Phil. Soc, 22, pp. 400-404 (1924). It is frequently 

 pointed out that RaE emits no perceptible gamma-rays, a fact which makes it seem 

 additionally probable that all the_ electrons which it emits come from the nuclei. 

 This does not prove anything, as it is conceivable that gamma-rays are emitted which 

 extract electrons from the electron-layers with such efficiency that no appreciable 

 fraction of them escapes unconverted. 



