li.ti:»] on Radiations from Exploding Atoms 490 



As was anticipated, it was found that the y rajs from radium B 

 and radium C gave w^ell-marked line spectra. The general method 

 employed was to use an a-raj tube containing a large quantity of 

 emanation as a source of radiation. The y rays w^ere reflected from 

 a crystal of rock-salt, and the position of the spectrum lines deter- 

 mined photographically. Usually twenty-four hours were necessary 

 to obtain a marked photographic effect. Special difficulties arose in 

 these experiments which are absent in an investigation of a similar 

 kind with X-rays. In addition to y rays, the radio-active matter 

 emits very penetrating y3 rays which have a strong photographic 

 action ; while the y rays in their passage through matter themselves 

 give rise J to high-speed /5 rays. The disturbing effect of these 

 radiations has to be eliminated by placing the whole apparatus 

 between the poles of a powerful electromagnet. In this way it was 

 found that the spectrum of radium B consisted of a large number 

 of lines, of which the most intense were deflected at angles of 1° 46', 

 10°, and 12°. The more penetrating radiation from radium C gave 

 a strong line of 1° and a fainter line at 43'. The strong lines at 

 10° and 12° are due to easily absorbed y rays, and undoubtedly 

 correspond to the " L " radiation of radium B. The line at 1° 

 corresponds to a very penetrating radiation which has a wave-length 

 less than one-tenth of an Angstrom unit. The penetrating y rays from 

 radium C have by far the shortest wave-length so far observed. It 

 does not seem probable that such short waves can be produced 

 artificially in an X-ray tube unless possibly an exceedingly high 

 voltage be applied. 



There is one interesting result of these investigations that should 

 be mentioned. The two strong Lines of the radium B spectrum 

 deflected at 10° and 12° were found to correspond exactly in position 

 to the X-ray spectrum of lead. These experiments thus confirmed 

 the view based on chemical evidence that radium B and lead were 

 isotopic, i.e., they were elements of practically identical chemical 

 and physical properties, although their atomic weight differed by 

 seven units. 



COXNECTIOX BETWEEN (i AND y RaYS. 



Before considering in detail the diflicult problem of the connection 

 between fi and y rays, it is desirable to summarise the main facts 

 that have been established in regard to the relations between kathode 

 rays and X-rays : — 



(1) A small part of the energy of kathode rays falling on a 

 radiator is converted into X-rays, the average frequency of the latter 

 increasing W'ith the velocity of the kathode particle. 



(2) X-rays in passing through matter give rise to a /5 radiation. 

 The initial energy of the escape of the electrons increases with the 

 frequency, and is probably proportional to it. 



