404 



V. M. Zaporozhetz and E. M. Filippov 



the tube is filled. The grid 2 prevents the electrons ejected from the target 

 1 to fall on to the grid 3. 



The distance between the electrodes and the grid is chosen so as to exceed 

 considerably the average free path of the gas ions under a particular pres- 

 sure. As a result on the way from the electrode to the grid the ions undergo 

 many collisions with the gas molecules, thus evoking its additional ioniz- 

 ation. 



The distance between the grid and the target is chosen so that it is smaller 

 than the free path of an ion. 



The difficulty of producing such a tube lies in the fact that with the mini- 

 mum gas pressure, which is necessary to ensure a sufficiently energetic run- 

 ning of the process of ionization (10~^ to 10~^ mm Hg), the average free path 



E3 



+ - 



X 



E, 



Fig. 4. A basic plan of a sealed acceleration tube with equal pressures at the ion 

 source and the tube. 



of the ions becomes smaller and the target 1 and the grid 3 of the tube have 

 to be so near to each other that it is difficult to insulate them from each other 

 owing to the high potential necessary for the effective running of the nuclear 

 reactions. 



Another disadvantage of such a tube is its lower efficiency compared 

 with the tubes of normal type. Whereas in the normal tubes the ratio of the 

 intensity of neutron radiation to the current strength of the accelerated 

 ions is usually equal to 10^ n/sec fxK in tubes with deficient discharge it 

 does not exceed 10^ n/sec /^ A. 



It is necessary to point out that if the sealed tube is filled with deuterium 



