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XLIII. On some Properties of the Active Deposit of Radium. 

 By S. Ratner (Petrograd), Research Student, University 

 of Manchester* . 



1. INTRODUCTION.— The phenomenon of the spreading 

 of the active deposit of Radium has been observed long- 

 ago, and recorded by a large number of experimenters. In 

 some cases (for instance, in that described by Miss Brooksf) 

 the phenomenon is now easily explained by the action of 

 radio-active recoil ; in other cases, however, it appears to be 

 of a more complicated nature, and some further assumptions 

 are required for its explanation. Fajans % and others have 

 assumed that the active deposit of radium is slightly volatile 

 at ordinary temperatures, while Russ and Makower § sug- 

 gested that the radio-active atoms are partly deposited on the 

 surface in groups which may be set free by recoil when an 

 a-particle is ejected from one of the atoms in the group. The 

 phenomenon, however, has never beon subjected to special 

 investigation, and is recorded only as a source of error. 



In the present paper the results are given of various expe- 

 riments undertaken with the purpose of a detailed study of 

 the phenomenon. 



2. Procedure of experiments.— For the greater part of the 

 experiments a simple apparatus was used, consisting of two 

 insulated brass plates A and B (fig. 1), the distance between 



Fig. 1. 

 C 



which could be varied from zero to a few cm. The central 

 part of the upper plate A consisted of a disk C which could 

 easily be removed from the apparatus and replaced by a 

 similar one. In the centre of the plate B a small plate R 

 coated with the active deposit of radium could be fixed. 

 The active matter was always found to expand from the 

 plate R to the disk C ; and the experiments mainly consisted 

 in analysing the activity acquired under different conditions 

 by the disks. When RaA was expected to be present on the 

 plate R, a strong electric field (of the order of 10,000 v/cm., 



* Communicated by Prof. Sir E. Rutherford, F.R.S. 



t Miss Brooks, < Nature,' 1904. 



% Fajans, Phys. Zeit. xii. p. 369 (1911). 



§ Russ and Makower, Phil Mag. xix. p. 100 (1910). 



Phil. Mag. S. 6. Vol. 36. No. 215. Nov. 1918. 2 E 



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