Disintegration Products of Uraniu) 



427 



of the curve is practically an exponential curve with /j, about 

 oOO (cm.) -1 for aluminium. 



Fig. 4. 



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Ph ? 



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a 9 



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Thickness of aluminium, one foil corr. about 0*5 cm. of air 



In the above experiments the electroscope was covered 

 with 0*00025 cm. of aluminium; but if the electroscope was 

 used without an aluminium leaf, the effect due to the product 

 is a little more than doubled (see fig. 5, p. 428). 



The /3 radiation is about 25 per cent, of the total, and the 

 absorption coefficient of the a rays in aluminium calculated 

 in the ordinary way is about 2500 (cm.) -1 , and is about that 

 to be expected for a. rays of average range. rp his a. ray effect 

 cannot be attributed to a small quantity of uranium in the 

 film, for it is seen that the rapid drop in the absorption curve 

 disappears in a few days. The preparations were examined 

 after about two months, and it was found that the activity 

 due to traces of uranium could be only about 0*1 div. per 



