Possibility of separating Isotopes. 533 



complete separation would be achieved, so that it is worth 

 while inquiring into the quantities of the oases obtainable in 

 the case of neon. 



The maximum separation of the parabolas corresponding 

 to masses 20 and 22 (obtained when electric deflexion 6 is 

 half the magnetic) is approximately 



_1 Mr-Mg. _ 6 

 x/2 Mi U ~2*' 



Taking a reasonable value of 6 as '3 the maximum angular 

 width of the beam for complete separation =*01. If the 

 canal-ray tube is made in the form of a slit at 45° to axes, 

 i. e. parallel to the curves, the maximum angular length of 

 the beam might be say 5 times as great, which would 

 collect the positive rays contained in a solid angle of 

 •0005 sq. radian. 



The concentration of the discharge at the axis of the 

 positive ray bulb is considerable, and may be roughly 

 estimated to correspond to a uniform distribution of the 

 entire current over a \ sq. radian. One may probably 

 assume that half the current is carried by the positive rays, 

 and that at least half the positive rays consist of the gases 

 desired. If neon is analysed by this method therefore the 

 total current carried by the positive rays of mass 20 is 



•0005 x4x|xixi= -0005 i. 



If i is as large as 5 milliamperes this =1*5 X 10 4 E.S.U. 



2-7 x 10" x 4-77 x 10-° - = V * X 10 °' C - /SeC -' 



i. e. one might obtain about one-tenth of a cubic millimetre of 

 neon and T J cubic millimetre of metaneon per 100 seconds 

 run. 



The chief difficulty is the excessive cold necessary in the 

 receiving vessels which must be sufficient to fix the molecules 

 even at the extremely low pressure of 10~ 4 mm. in the 

 camera. This could be obtained by the use of liquid helium, 

 but whether charcoal cooled by liquid hydrogen would suffice 

 is at present uncertain. No such difficulty occurs of course 

 in the separation say of the lead isotopes, but so far it has 

 not proved possible to obtain lead positive rays quite 

 apart from the difficulty of separating the parabolas when 

 obtained. 



