Passage of a Particles through Hydrogen. 825 



source of about 25 millicuries of radium emanation contained 

 in an a-ray tube was mounted inside a sbeet-iron cylinder so 

 that it could be moved along the tube by a hand electro- 

 ma cr net. 



The tube was rilled with hydrogen at atmospheric pressure, 

 and scintillations counted on the zinc-sulphide screen for 

 different distances between S and Z. 



The following numbers were obtained : — 



Distance of a-ray tube 

 to screen Z. 



Scintillations 

 per minute. 



24cm 



38 „ 



End of range of a particles. 

 10*0 per minute. 

 O'O „ ,, 

 0-5 „ 



50 „ 



82 „ 





With air at a pressure adjusted to give the same range of the 

 a particles, i. e. about 17 cm. Hg, the number of scintillations 

 decreased very rapidly after the end of the range, falling 

 to 0*5 per minute at 26 cm. The results show that in 

 hydrogen, particles capable of producing scintillations are 

 produced which can travel at least 3^ times as far as the 

 a particles. That these particles are actually generated in 

 the hydrogen is shown by the following experiment : — A 

 similar iron cylinder to the one carrying the source was 

 placed inside the tube between S and Z. Over the end of 

 this cylinder sheets of aluminium equal in stopping power to 

 8 cm. of air were fastened. The distance SZ was 17 cm., 

 and by manipulation of a hand electromagnet the foils could 

 be placed either near to the source S or the screen Z. In 

 the former case the s. particles were altogether absorbed by 

 the aluminium and did not emerge into the gas beyond. The 

 following results were obtained : — 



Tube. 



Al foils. 



No. of Scintillations 

 per minute. 



Exhausted to 1*5 cm. Hg ... 

 Hydrogen at 76 cm. Hg 



Near Z 



ii it 



Near S 



07 

 7 75 

 013 



