[ 690 ] 



LXXI. On the /3-RecoiL By Aniela Muszkat, 



Radiological Laboratory, Warsaw *. 



I^HE experimental evidence concerning the /3-recoil radia- 

 tion, as resulting from former publications on this 

 subject, is in some points insufficient. Makower f and Russ 

 established the existence of the phenomenon, but there are 

 some doubts concerning the exceedingly small recoil efficiency 

 observed, and the impurity of the recoil product. 



Makower and Russ have tried to explain their results by 

 supposing that the active deposit forms agglomerations on 

 the surface of the activated bodies, these agglomerations 

 exercising a strong absorption on the recoiling atoms. This 

 hypothesis is not improbable in itself. The mechanism of 

 the deposition of active matter may resemble the condensation 

 of vapour on a cold surface, in which case there are small 

 droplets formed instead of an uniform layer. However, if 

 the quoted authors are right, then the deficiency ought to 

 depend upon the mean surface density, being greater for the 

 less active surfaces. As this does not occur, one must 

 search for another explanation. 



Mr. Wertenstein suggested to me that the absorption of 

 the recoiling atoms may be due to two different causes : (1) 

 an adsorption of a gas layer on the activated surface, the 

 electric transport of the gaseous ions during the activation 

 contributing greatly to this adsorption ; (2) the penetration of 

 the active deposit by diffusion into the mass of the activated 

 body. The only possible way of eliminating these presumed 

 causes of error seems to be in obtaining a layer of active 

 matter by distillation in vacuo, and examining the recoil 

 from this layer immediately after the distillation. In the 

 present work I adopted a method based on this idea. 



A platinum wire, made active with RaB + C in the usual 

 way, was placed very near the surface to be coated with 

 distilled RaB. By the use of a ground-glass piece, this 

 surface J could rotate through 180° and in this way direct its 

 recoil stream on a receiver. The apparatus I used at first 

 was very simple, but an unexpected difficulty compelled me 

 to make it far more complicated. It wjas hoped that the 

 "cold disk '• would act as a perfect screen to the distilling 

 matter, the atoms of RaB travelling in vacuo on straight lines 

 and being retained — as I thought — by the disk, after they 



* Communicated by Dr. L. Silberstein. 



t Phil. Mag. vol. xix. p. 100 (1910). 



1 Called in this paper for the sake of briefness, " the cold disk." 



