Beta Rays and by Gamma Rays from Radium C. 561 



agrees well with the measurements of Rutherford and 

 Barnes, who obtained an increase of about two calories an 

 hour, when about one-half to one-third of the 7 rays were 

 absorbed in a lead cylinder. 



The energy required to make an ion may be calculated 

 from any of the above relations, and the results must, of 

 course, be concordant. 



The value obtained is 5*2 xlO" 11 erg per ion. If the 

 work required to produce an ion is e 2 /r, where r is the radius 

 of a molecule, it follows that the radius of a molecule is 

 0*46 x 10~ 8 cm., a result of the right order, but apparently 

 somewhat small. Townsend has found that the minimum 

 energy required to make an ion is 2*5 x 10 ~ n erg. 



If the old view of the y rays is examined, which supposed 

 that the expulsion of a /3 particle caused an electromagnetic 

 pulse with uniform distribution of energy near a spherical 

 shell, some remarkable results follow. The work of AVulf * 

 on the penetration radiation on the Eiffel Tower indicates 

 that the 7 rays from radium and thorium in the earth reach a 

 height of 300 metres, and ionize there. This paper shows 

 that the mean range of a 7-ray disturbance is 250 metres. 

 It has already been pointed out that Townsend found the 

 minimum energy required to make an ion to be 2*5 x 10 ~ n erg, 

 and that such an ion ma}^ be produced by 7 rays at 300 m. from 

 the radioactive source. If A is the area of the cross-section 

 of a molecule, we have over a surface A at distance 250 m. 

 from the centre at least 2*5 xlO -11 erg. Therefore, over 

 surface A at 1 cm. from the source there must be an energy 

 2-5 x 10- 11 x (25,000) 2 , or -015G erg. 



As about 3 '4 x 10 10 ft particles leave a curie of radium C 

 every second, there will be the same number of y pulses, and 

 we have 3'4 x 10 10 x '0156, or 5 x 10 8 ergs per second, as a 

 very moderate estimate of the power of the 7 radiation. 



But the whole power of all the radiations from a gramme 

 of radium is only 1*3 x 10 6 ergs per second ! 



It therefore seems impossible to consider the radiation as 

 a spherical shell with uniform energy over the surface, and 

 also impossible to contemplate the 7 radiation as expanding 

 conical ly. It must be linear, whether electromagnetic or 

 corpuscular. As the 7 radiation is mainly independent of 

 the concentration at the source, it does not seem possible 

 to conjure up a train of pulses, or overlapping of pulses, or 

 any such interference effects to account for the energy 

 necessary for ionization. 



* Phys. Zeit. Sept, 15, 1910. 



