THE USE OF ACCELERATORS OF CHARGED PARTICLES 



401 



ium, etc. It is established that a few minutes after the end of irradiation by 

 fast neutrons the gamma rays activity in sandstones is already considerably 

 higher than in shales, limestones, etc. 



Since under the conditions prevalent in bore-holes the activation of rocks 

 will happen both due to the fast and to the retarded neutrons, in order to 

 develop the fast neutron rock activation method of investigation it is ne- 

 cessary to use an intermittently-operating neutron source. 



PRINCIPAL CONSTRUCTION PROBLEMS OF A WELL NEUTRON GENERATOR 



A normal well neutron generator is shown diagrammatically in Fig, 3. 

 Its princij)al constituent parts consist of an ion source, an acceleration tube, 

 a generator of high potential and a target. The ions which form in the ion 

 generator fall into the acceleration tube. Here they are accelerated in the 

 electric field, produced by the high-voltage generator, and bombard the 

 target. Depending on the nature of the target and the ionized gas selected 

 a certain nuclear reaction occurs, which results in the production of a specific 

 radiation. The most widely used neutron generators are those in which ions 

 of deuterium bombard a zircon-tritium target to produce the reaction 

 H^(c?, n) He*, evolving neutrons, with an energy E^ on average near to 



ICT) Cp CO 



1 



_ ^ . 



100-200 kV 



Fig. 3. A basic construction scheme of a neutron generator. 1 — an ion source with 

 gas pressure of 10~^-10~^ mm Hg; 2 — an acceleration tube with gas pressure of 10"^ 

 -10"^ mm Hg; 3 — a generator of high potential; 4 — zirconium — tritium target; 5 — - 

 vacuum pump; 6 — a tritium filled cavity, connected via a palladium ventilator, with 

 the ionization chamber; 7 — ionizer. 



Applied geophysics 26 



