Collisions of a Particles with Hydrogen Nuclei. 



929 



7-ray activity was usually equivalent to from 5 to 10 mg. 

 Ra. When the source and diaphragm were in position, 

 the box was evacuated, and the H particles falling on the 

 ZnS screen were counted. 



§ 5. Ranges of ' H particles projected at known Angles. 



It was stated in § 2 that, if the laws of conservation of 

 energy and momentum hold in these collisions, the range R 

 of an H particle projected at an angle 6 is given by 

 R = R cos3 0> where R is the range of the H particle 

 projected in the line of motion of the a particle. 



At various times during the experiments, measurements 

 of the ranges of the a particles observed between known 

 angles were made by inserting aluminium screens of known 

 stopping-power between the opening and the ZnS screen. 

 It was found that the maximum range R of the H particle, 

 measured in aluminium and expressed in equivalent cm. of 

 air, was 30 cm. 



Fig. 3. 



6 



















*~ c 



r -M. 















■ 



I 

 I 4 

























1 















} 



1 













) 













I 



























oy 









_____ 











55K^~~ -© . 



16 



fierce in cms. of a/n 



20 



24 



In one set of experiments, a sheet of paraffin wax of 

 effective thickness 8*0 fi or 8*7 mm. stopping-power was 

 used on a diaphragm of! angular limits 21°'I to 31°*3. The 

 greatest range of the H particles observed on the screen 

 should then be 24*2 cm , corresponding to an angle of 21 c- 4 

 and an a particle of range 7'0 cm., and the least range 

 should be 16*3 cm. for an angle of 31°*3 and an a particle 

 of range 6*13 cm. 



The curve of fig. 3 shows the experimental results. 



2S 



