produced by Partly-absorbed Gamma Rays. 431 



to the frequencies that Rutherford and Andrade* found 

 for the 7 rays of RaB and RaC respectively. Further, 

 Rutherford, Robinson, and Rawlinson f , by using an eman- 

 ation-tube wrapped in lead foil, obtained the magnetic 

 spectrum of secondary /3 rays produced from lead by the 

 7 rays of RaB and RaC, and found that all the observable 

 lines were nearly, if not quite, identical with the primary 

 /3-ray lines of RaB. Lines corresponding to the faster 

 primary ft rays of RaC were probably also present, but were 

 difficult to observe with certainty owing to their relative 

 faintness and the fogging from scattered radiation in this 

 region of the plate. It is thus indicated that the secondary 

 ,/3 rays produced from lead by the 7 rays have a spectrum 

 identical, or nearly so, with that of the primary /3 rays and 

 therefore, like the latter, derive their energy in quanta from 

 the 7 rays. 



The question then arises whether the number of quanta 

 which 7 rays of given frequency may impart to secondary 

 ,/3 particles is independent of the energy of the impinging 

 y rays, or whether the 7 rays, when they lose energy in 

 passing through matter, may lose also the power of producing 

 (3 rays of great energy — whether, for instance, 7 rays that 

 originally can impart energy 5/iv to an electron may be able, 

 after passing through a centimetre of lead, to impart at most 

 the energy 3hv. For it seems probable that in passing- 

 through matter 7 rays may lose energy in some other way than 

 by the production of/9 rays. Thus the scattering of 7 rays 

 investigated by FloranceJ may be due to the forced vibration 

 of electrons that remain in the atom, and therefore absorb 

 less energy than those projected as secondary j3 rays. If 

 this is so, we should expect that the 7 rays, after passing- 

 through a considerable thickness of matter, would be, as it 

 were, shorn of some of their available quanta, and that 

 therefore their secondary j3 radiation would be, on the whole, 

 less penetrating than that of the unaffected 7 ra} T s. 



It was to investigate this point that Sir Ernest Rutherford 

 suggested the present research, which is a modification of a 

 research carried out by Eve § in 1904. 



It was found that if this effect of matter on the 7 rays 

 exists, it lies beyond the range of the method used. 



* Rutherford and Andrade, Phil. Mag. xxvii. p. 854 (1914) ; Phil 

 Mag. xxviii. p. 263 (1914). 



t Rutherford, Robinson, and Rawlinson, Phil. Mag. xxviii. p. 281 

 (1914). 



X Florance, Phil. Mag. xxvii. p. 225 (1914). 



§ Eve, Phil. Mag. viii. p. 669 (1904). 



