524 McCoy and Ashman — Urano-TJ ranic Oxide. 



The activity measurements were made in a gold-leaf electro- 

 scope having an ionization chamber 19*5 cm square and a dis- 

 tance of 8'5 cm between the film and the electrode of the 

 gold-leaf system. The scale of the micromoter microscope cor- 

 responded to potentials between 576 and 473 volts, the fall of 

 potential across the scale being 103 volts. Our standard films, 

 which had about 0*020 g. of oxide per sq. cm., were all suffi- 

 ciently thick to have the maximum a-ray activity. The /3-ray 

 activity was small, but varied with the weight of the film. It 

 was also evident from the nature of the /3-rays that the observed 

 activity of the latter must depend upon the size of the ionization 

 chamber, which in the case of our electroscope, though large 

 enough to get the maximum effect of the a-ray s, was insufficient 

 for the /3-rays. We have determined the /3-ray activity for 

 our electroscope in the following manner : The standard films 

 of U 3 8 were covered with one to four pieces of aluminum 

 foil # 0043 cm thick and the resulting /3-ray activity measured. 

 The first layer of foil cut off all the a-rays and a portion of the 

 /3-rays. By graphical extrapolation of the curve having /3-ray 

 activity and number of foils as coordinates, it was found that 

 this portion amounts to 9*2 per cent of the effective /3-ray 

 activity of the uncovered film. 



The further data for the films made from samples A, B, and 

 C are given in Table II, the activity being expressed in terms 

 of an arbitrary unit. 



Table II. 



Films in tin dishes 7'15 cm in diameter with rims 0'8 cm high. 



a and (3 

 Sample No. Weight Activity (3 Activity* a Activity 



A 9 0-816 10080 0-0108 0'9972 



A 10 0-807 1*0075 0-0100 0'9975 



B 18 0820 0-9990 0*0020 0*9970 



B 19 0-753 1-0005 0-0020 0'9985 . 



C 13 0-920 1-0040 0-0110 0'9930 



C 14 0-892 1-0010 0-0110 0'9900 



C 15 0-793 1-0070 0-0154 0'9916 



Films on flat copper plates 7-00 cm in diameter. 



A 23 0-694 1-1111 0-0296 10815 



A 25 0-625 1-1080 0'0262 1-0818 



B 24 0-629 1-0950 0*0133 1-0817 



These results show that the method of making U 3 8 gives a 

 product of definite activity. The somewhat low activity of 



* The activities were measured before the maximum amounts of UX, 

 which had been largely removed in the process of purification, had again 

 accumulated ; for this reason the /3-ray activity of a film is not a definite 

 function of its weight. 



