Ions prodvced by (3 and 7 Radiations from Radium. 331 



these, the extrapolation can be made with sufficient accuracy 

 from knowledge of the numbers and absorption coefficient of 

 the different types o£ (3 radiation emitted by radium B and 

 radium 0. The total ionization N was calculated by means 

 of equation (1) from the area included by the curve, so that 

 any error in the extrapolation had little effect on the final 

 result. The ionization by both /3 and 7 radiations up to 

 3 metres was in this way found to be 6*42 X 10 13 X 47r. It 

 will be shown later that of this only 0*18 X 10 13 x 4-7T was due 

 to the 7 radiation, leaving 6*24 x 10 13 x47r for the ionization 

 by the /3 particles. From 3 metres onwards the value of 

 nr 2 , after the 7 ray effect had been subtracted, was found 

 to fall off exponentially, the value at 3 m. being 6*0 x 10 ia 

 and the absorption coefficient '0056 cm. -1 . From these data 

 the total /3 ray ionization from 3 m. onwards was found by 

 means of equation (3) to be 1*07 x 10 13 X 47T, and adding this 

 to the ionization up to 3 m. the total value of N was 

 9'20xl0 14 . This result has been calculated in terms of the 

 Rutherford-Boltwood radium standard, which is now known 

 to contain 5 per cent, less radium than its nominal value. 

 The corrected value for N, the total /3-ray ionization from 

 radium B and radium C, is 9'65xl0 14 pairs of ions per 

 second per gram of radium on the international standard. 



The Effect of the ft rays from Radium C alone. 



No attempt has been made in these experiments to separate 

 the yS ray effects of the two contributory transformations. It 

 is, however, possible to calculate approximately the relative 

 numbers of ions produced by radium B and by radium O. 

 An equal number of particles is emitted in the two cases *. 

 Those from radium B have an absorption coefficient of about 

 100 cm. -1 in aluminium. Those from radium can be 

 divided into two groups f, of which about 50 per cent, have 

 \=50 cm. -1 and the rest \ = 13 cm. -1 . Further, the number 

 of ions produced per cm. in air is a known function of X i, 

 and allowing for this factor the values of N for the two 

 transformations should be in the proportion 



160 1/120 80\. ... ... 



IOO : 2Uo + lT5) (::34:6(,) - 



From this we obtain the estimated value for the/3 radiation 

 from radium C alone G*ixl0 u pairs of ions per gram per 

 second. 



* Moseley, Proc. Rov. Soc. A. lxxxvii. p. 230 (1912). 

 t Ibid. p. 241. 

 t Ibid. p. 248. 



