THE USE OF ACCELERATORS OF CHARGED PARTICLES 405 



and a tritium, target is being used, as a result of the change in the gas 

 content in the tube, conditioned by the diffusion exchange of the target and 

 the tube hydrogen, there arises a certain degree of instabihty in the work- 

 ing conditions of the tube. This can be avoided if a mixture of deuterium 

 and tritium is introduced into the tube. In such a case, when small 

 accelerating potentials are employed, the principal role is played by the 

 reaction H*(c?, re) He* since on collision vdih deutrons the cross -section 

 of this reaction is considerably smaller. Evidently the filling of the tube ^vith 

 a mixture of H^ and H^ lessens the neutron emission by approximately 

 half, per unit of strength of the ion current, in comparison with values 

 obtained when the tube is filled with a single-component gas, since in the 

 former case nearly half of the collided hydrogen atoms would be used up 

 in useless reactions H^ {d, n) He^ and H^ {d, n) H^. On the whole we consider 

 the testing of a sealed tube in a well neutron generator to be important. 



3. Use of absorbents 



It is possible to avoid the installation of a vacuum pump in a well neutron 

 generator by placing an absorbent in the acceleration tube. Titanium, tanta- 

 Uum, zirconium and certain other substances can be used as absorbents of 

 hydrogen. For instance, it is known that under a pressure of ~10~* mm Hg 

 titanium on heating up to 200 °C (optimal temperature of absorption) 

 is capable of absorbing up to 1700 cm^/g of hydrogen. 



As a result of experiments conducted by G. D. Glebova^*) it follows 

 that at a temperature of about 40°C the velocity of absorption of hydrogen 

 by metallic titanium is approximately equal to 60 cm^H/cm^ Ti sec. Obviously 

 the velocity of absorption of deuterium would be 1/2 times less. 



Let us determine the probable velocity of arrival of hydrogen — derived 

 from an ionic source — into the acceleration tube. 



Experience of using neutron generators shows that the relationship between 

 the intensity of the neutron radiation and the current strength of 

 accelerated ions is usually equal to lO^n/sec ^aA. Consequently, to obtain a ra- 

 diation of lO^n/sec a current of 10 //A is necessary in which case 6.25 — 10^^ ions 



10 n/sec 



per second are transported. Thus, — XlOO% = 1.5X10^ 



6.25 X 10^^ ions/sec 



per cent ions of deuterium react with the tritium of the target. Adopting 

 the ratio of the atomic to the molecular ions to be equal to 0.5 and an ionic 

 source as given above, we obtain the velocity of arrival of the gas into the 

 acceleration tube to be 3.6 x lO^^D/sec or 1.7 x 10^ cm^/sec under atmospheric 

 pressure. This implies that the increase in the gas content of the acceleration 

 tube in operating a neutron generator is so small that with the aid of an 



