582 ADVENTURES IN RADIOISOTOPE RESEARCH 



injection of the active blood took place. This sample is hemolysed as 

 well, and treated similarly to the standard sample. It is of the greatest 

 importance to compare the activity of dry blood samples having the 

 same corpuscle — plasma ratio. This is facilitated by preparing the sam- 

 ples from hemolysed blood. 



Thorium B and its Disintegration Products 



Before describing the measurement of the activity of the ThB-labelled 

 blood samples, it is appropriate to recapitulate our knowledge concerning 

 the disintegration of the active deposit of thorium, and the radiation 

 emitted which follows this disintegration. 



The sequence of the radioactive disintegration products of radio- 

 thorium (RaTh) is shown in the following schema: 



Thorium B emits, as seen from the above schema, soft /5-rays, which are 

 half-absorbed by a blood layer of 0.4 mm thickness. The disintegration 

 products of ThB, ThC andThC " emit 7.5 times and 4.8 times as penetrat- 

 ing ^-rays as ThB. Furthermore, ThC and ThC" emit a-rays having a 

 range of 31 //, and ThC with a range of 56 ju, in dry blood; y-rays are 

 •emitted as well. To what extent these radiations participate in producing 

 ions in the Geiger tube, depends on the thickness of the layer, that of 

 the window of the counter and the volume of the counter. The complexity 

 of the radiation emitted by ThB and its disintegration products is in no 

 way disturbing, as we are solely interested in the comparison of the 

 activity of blood samples emitting the same complex type of radiation. 

 When we use thin window counters, as applied when measuring the 

 activity of i^C, some of the strongly ionizing a-rays emitted by the dry 

 blood sample penetrate into the counter and contribute to the total 

 number of counts produced. When we use glass cuvettes, however, 

 these and other soft rays are stopped by the window of the cuvette; 

 furthermore, these, and also harder rays, are partly absorbed by the 

 water content of fresh blood. If we wish to administer a very restricted 



