930 Dr. J. Chadwick and Mr. E. S. Bieler on the 



Within the accuracy of experiment, the measured ranges,, 

 after allowing for the fact that the H particles travel 

 through the screens at an angle, agree with the calculated 

 ranges, indicating that there is no appreciable loss of energy 

 in these collisions, such as might occur owing to radiation 

 or to the conversion of translational energy into rotational 

 energy. 



§ 6. Angular Distribution of the H 'particles. 



The relation ?i = ~F(0) has been investigated carefully 

 up to an angle of 48°*4 for the impact of a. particles of 

 average range 6' 6 cm. 



The following diaphragms were used : — 



Diaphrain A, for which = and 6=11°% 



B, „ „ 21°'4, 



0, „ 21-4 „ 31°-3, 



D, „ 31°-3 „ 41°-0, 



„ . E, „ 41°-5 „ 48°'4. 



Each diaphragm carried a sheet of paraffin wax of 

 effective thickness equal to 8'0 fi, equivalent to 1*22 cm. 

 of hydrogen gas at N.T.P. Its stopping-power was equal 

 to 8*7 mm. of air. The range of the incident a particles 

 was 7*0 cm. ? and their average range in the paraffin sheet 

 was 6' 6 cm. 



The distance from source to diaphragm, and from 

 diaphragm to screen, was 26*8 mm. 



In the case of diaphragms A and B, the H particles 

 observed on the screen consisted partly of the so-called 

 " natural " H particles *. These are supposed to be due to 

 a slight hydrogen contamination of the source or any 

 absorbing foils in the path of the a rays. All foils which 

 were exposed to the ol rays were heated in vacuo to reduce 

 the number of these ''natural"" particles to a minimum. 

 Their number was found by observations when the dia- 

 phragm and paraffin were removed, and was usually about 

 1*5 per minute per mgm. activity of the source. 



With the other diaphragms no correction of this kind was 

 necessary, for the central disk of the diaphragm stopped the 

 " natural " H particles completely. 



The second column of the following table gives the 



* Eutlierford, loc. cit. p. 544. 



