596 ADVENTURES IN RADIOISOTOPE RESEARCH 



of the erythrocytes takes only minutes, and the ThB is better retained by 

 the red corpuscles than 32p or ^'-K. Since the plasma is practically inactive, it does 

 not have to be removed before injection. This very convenient method (59) has 

 two drawbacks. Emanating radio-thorium preparations which are precipitated 

 with iron hydroxide lose with time much of their emanating power, as already 

 noticed by Otto Hahn to whom this method of preparations is due. The dis- 

 integration products of ThB, which are the ThC products, emit a -particles. These 

 densely ionizing particles are several times as biologicaUy effective than f^- or 

 y-rays. The increasing biological activity of the a-rays is compensated by the short 

 hfe-time of ThB, and correspondingly the subject investigated is exposed to radia- 

 tion for a short time only. The not entirely unjustified reluctance to achninister 

 a-rays emitting radioactive substances to human subjects, is responsible for the 

 fact that this method has not found an extensive appHcation. 



References 



H. BoHB (1954) Bestemmelse af Blodvolumet med radioaktivt Fosfat. Schuhz For- 



lag, Copenhagen. 

 G. Nylin (1945) Ark. Kemi A 20, 1. 

 O. Nylin (1953) Acta Med. Scand. 147, 275. 

 P. F. Hahn, W. M. Balfour, J. F. Ross, W. F. Bale and G. H. Whipple (1941) 



Science 93, 87. 

 E. Alexander (1953) Ark. Kemi 4, 304. 



