by a, Particles jrom Radium Emanation. 921 



Table IT. shows these radiations and qualities. The 

 numbers are for jn/p in aluminium. 



Table II. 



Gold. 



Platinum. 



Lead. 



Tin. 



21-0 

 0-25 



13-4 

 0-32 



13-0 

 0-22 



1-85 



Discussion of Results. 



The outstanding feature of this investigation is that with 

 each of the elements of high atomic number two radiations 

 are emitted when bombarded by a particles, which in quality 

 are of the order of their (i Characteristic Radiations'''' of the 

 "K" and "L" types. Tin, an element of medium atomic 

 number, emits one radiation of the order of its " K " radia- 

 tion, but the method used could not possibly detect a soft 

 type of the order of its " L " radiation. 



The relative intensities of the two types of radiation 

 cannot be compared correctly owing to experimental diffi- 

 culties. The investigation of the soft radiation was carried 

 out with the grid-tube, but with this arrangement the 

 amount of radiation excited is, for reasons given before, too 

 small to measure accurately when more than 2 mm. of 

 absorbing aluminium is interposed, and the hard radiation, 

 deduced from the flat part of the curve (see fig. 5), was 

 determined with the thin glass tube arrangement. Thus a 

 comparison of the relative intensities depends on an un- 

 certain grid factor and cannot be made with certainty. 



These determinations were rendered veiy tedious and 

 difficult by the extremely small quantities to be measured. 

 It is remarkable that even when the total absorbing thickness 

 of aluminium is only 0*1 mm., the quantity of radiation 

 excited in platinum is only of the order of 0*5 per cent, of 

 the maximum equilibrium y radiations. Thus several deter- 

 minations were necessary for one mean point. 



Another surprising fact is that the disintegrating emana- 

 tion atom emits so little radiation, if any. It is difficult to 

 believe that no active deposit is carried over with the 

 emanation, and this would easily account for fche initial 

 activity observed when paper is the target bombarded, and 

 the absorption thickness is at a minimum. 



Phil. Mag. S. 6. Vol. 42. No. 252. Ay. 1921. 3 P 



