326 Radium Constants on the International Standard. 



complete accord with the value o£ nE deduced by direct 

 measurement and by determining the volume of helium pro- 

 duced from radium. 



We have in the above made no assumptions as to the form 

 in which the energy is emitted from the external distribu- 

 tion of electrons, but have supposed that it ultimately appears 

 as heat. It is, however, implicitly assumed in the calcula- 

 tion that this energy is not emitted in the form of radiations 

 so penetrating that they are able to escape through the 

 absorbing material employed in the actual measurements. 

 No doubt part of the energy may be emitted (as possibly in 

 the case of radium itself) in the form of slow ft rays and soft 

 7 rays, but no certain evidence is available on this point. 



It follows from these considerations that the heating effect 

 of all ol ray products should be greater (on the average 

 about 10 per cent.) than the kinetic energy of the expelled 

 a particles. Similarly the heating effect due to a ft ray 

 transformation may in some cases be less than the value 

 calculated from the energy of the expelled ft particles, but it 

 is difficult to be certain how far the energy of the latter may 

 be affected by the change of nucleus charge. 



Life of Radium, 



The half-value period of transformation of radium can be 

 calculated at once from the value nE, without any assumption 

 of the actual value of n or E except that E is twice the 

 unit charge. On the International Standard, the half-value 

 period comes out to be 1690 years # , taking nE = 11*1 x 10~ 1(> 

 e. m. units. This is much less than the experimental value 

 found by Boltwood t, viz. about 2000 years, but is in better 

 accord with the value 1800 years given by KeetmanJ, and 

 1730 years found by Stefan Meyer §. 



Unless the determinations of nE from the charge carried 

 by the u particles, the production of helium and the heating 

 effect, are all seriously overestimated and to the same extent, 

 the value 1690 years cannot be far from the truth. It is 

 desirable that this important constant should be re-deter- 

 mined, and I understand that this is being undertaken by 

 Professor Boltwood and Mile. Grleditsch. 



It should be mentioned that the accuracy of the original 



* By an oversight, the period of radium was calculated as 1850 years 

 instead of 1620 years in ' Kadioactive Substances ' p. 459. The error 

 arose in the correction in terms of the International Standard. 



t Boltwood, Amer. Journ. Sci. xxv. p. 493 (1908). 



% Keetman, Jahrb. d. Radioakt. vi. p. 265 (1909). 



§ Wien. Ber. cxxii. p. 1086 (1913). 



