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ADVENTURES IX RADIOISOTOPE RESEARCH 



this tube is connected with a matching glass joint, which contains two 

 brass rods for the power supply and across the ends of which the activa- 

 ted platinum foil is fastened horizontally. The chamber B and the 

 vaporization chamber are evacuated and filled with nitrogen before the 

 pellet is lowered from A until it is near the top of the platinum foil G. 

 At a nitrogen pressure of 1 mm the foil is brought to a white heat (about 

 900°) for 1 sec and thus the vapour of ThB chloride is transferred on to 

 the surface of the pellet. 



Pumpe 



Fig. 1. 



The recoil product, ThC", emits ^-rays whose strength constitutes 

 an easily traceable measure of the recoil yield. The recoil product is 

 collected as follows : After first waiting until radioactive equilibrium has 

 been attained the pellet is placed in a tube attached at 8 above a copper 

 foil charged to —220 V, the pellet being earthed, and the recoil atoms are 

 collected on the copper foil. A decrease in the pressure to 2 cm aids the 

 collection of the recoil product. Measurement of the /5-activity of the 

 copper foil gives the recoil yield before the diffusion. 



