1915] on Radiations from Exploding Atoms 501 



of radium B. This striking result shows that those /? rays escaping- 

 from the radio-active atom wliich give rise to a line spectrum must 

 result from the conversion of y rays into /3 rajs in the radio-active 

 atom. The slight differences observed in the spectrum for different 

 metals is probably connected with the ene:gy required to excite one 

 of the characteristic radiations of the element used as absorber. 



An explanation of the marked differences in the character of the 

 p and 7 radiation from different radio-active atoms can, I think, be 

 given on the following lines. Some of the y rays are broken up in 

 their escape from the atoms, and the energy of each converted y ray 

 is transferred to an electron which escapes with a definite velocity 

 dependent on the frequency of the y radiation. Taking into account 

 a large collection of disintegrating atoms, each of the possible modes 

 of characteristic vibration of the atom gives rise to an electron of 

 definite speed. In this general way we may account for the line 

 spectrum of the /8 rays which is so commonly observed. On this 

 view, we should expect to obtain a well-marked line spectrum of /? 

 rays when a substance emits strong y rays — a result in accord with 

 observation. 



In order to account for the marked differences in the types and 

 intensity of y rays from different radio-active substances, it seems 

 necessary to suppose in addition that the primary ^ particle always 

 escapes from the nucleus in a fixed direction with regard to the 

 structure of the atoms under consideration. For example, we have 

 already pointed out that radium E, although it emits intense /8 rays 

 which give a continuous spectrum over a wide range of velocity, 

 emits very weak y rays. Since there can be no doubt that the /? rays 

 have satficient speed to excite the characteristic modes of vibration 

 which must be present in the atom, we are driven to the conclusion 

 that the y8 particle escapes in such a direction that it does not 

 pass through these vibrating centres. On this view, the type ol 

 characteristic y rays which are excited, and consequently also the 

 corresponding speed of the (B rays which arise from the converted y 

 rays, will depend entirely on the direction of escape of the primary 

 /? particle. The definite direction of escape of the primary (i particle, 

 which varies for atoms of different substances, also suffices to explain 

 a number of other differences observed in the mode of release of 

 energy from various radio-active atoms. It is supported by many 

 other observations which indicate that the atoms of a particular 

 radio-active substance break up in an identical fashion. 



We have so far considered only in a qualitative way the relation 

 between the groups of rays in a /?-ray spectrum and the emission of 

 characteristic y rays. During the last few years there has been a 

 growing body of evidence that the energy E carried off in an X-ray 

 of frequency v is proportional to this frequency, and is given by 

 E = /iy where h is Planck's fundamental constant. If the whole of 

 the energy of an X-ray can be given directly to an electron, the 



