u = 



Number of a Particles emitted by Uranium. 691 



A relation between P n (— /* ) and -= — P™ (yu ) exists in this 



CtfM 



case, and allows ns to pnt this result in the form 



4. Ji * P r ll) 



for ?•<?•', the values of n being as above. 



The symbols r, r y have to be interchanged when r>r\ and 

 if the source were at (V, 6', <f>') instead of at (V, 0, 0), a 

 corresponding, but more complicated, result would hold. 



The problems in conduction of heat analogous to these lend 

 themselves to the same treatment. 



Sydney, June 1910. 



LXXV. The Number of a Particles emitted by Uranium and 

 Thorium and by Uranium Minerals. By Hans Geiger, 

 Ph.D., and Professor E. Rutherford, F.R.S.* 



IN previous papers we have shown that the number of 

 a particles emitted per second from radioactive materials 

 can be counted either by the electrical or scintillation method. 

 It has been shown that one gram of radium itself, and each 

 of the three u ray products in equilibrium with it, emits 

 3*4 x 10 10 a particles per second. Since Rutherford and 

 Boltwood f have shown that in an old unaltered mineral 

 there is 3*4 x 10~ 7 gram of radium per gram of uranium, it 

 is possible to deduce the number of a particles emitted per 

 second from one gram of uranium and also from a mineral 

 containing one gram of uranium. In this calculation it is 

 supposed that uranium is the ultimate parent of radium, and 

 that the mineral is in radioactive equilibrium. If a uranium 

 atom, like a radium atom, emits one a particle in its trans- 

 formation, the number of a particles emitted per second per 

 gram of uranium should be 3'4 X 10 10 x 3'4 x 10" 7 , or 11,600. 

 We shall for convenience call this number N. 



As a result of a very careful analysis of the radioactive 

 constituents of uranium minerals, Boltwood % has shown that 

 the total activity of uranium, measured by the electric 

 method, is about twice as great as would be expected if 



* Communicated by the Authors. 



t Amer. Journ. Sci. vol. xxii. p. 2 (1906) ; also Boltwood, Amer. 

 Journ. Sci. vol. xxv. p. 296 (1908). 



X Boltwood, Amer. Journ. Sci. vol. xxv. p. 270 (1908). 



2 Z2 



