THE USE OF ACCELERATORS OF CHARGED PARTICLES 



399 



of neutron radiation, separated by intervals of time (several hundreds or 

 tens of microseconds) sufficient for the capture of all the generated neutrons, 

 and the scintillometer is smtched on for a short period after each spurt 

 then it is possible to register only the gamma rays produced by the initial 

 inelastic colHsions of neutrons \\ith atomic nuclei. 



50 



iOO 150 



A 



Fig. 1. Cross-section of an inelastic scattering of the neutrons with an energy 



of 14 MeV. 



The cross -section g of the inelastic scattering of the neutrons with an 

 energy of 14 MeV increases with the growth of the naass number A of the 

 scattering target. Experimental studies (^) show that the relationship be- 

 tween these quairtities is well approximated by the follo^ving equation. 



where : 



R = (2.5 + \.\A"'-) X 10-1=^ cm. 



For the light nuclei — -to Ashich category belong most of the rock-forming 

 elements — a lies within the limits of 0.5 to 1.2 barns (Fig. 1) (^). The rela- 

 tively small range of a in the rock-forming elements permits consideration of 

 the inelastic scattering to be approximately equally likely for all of them. 

 This circumstance precludes the possibility of carrying out neutron-neutron 

 logging ^dth the aid of high energy neutrons. The situation is different in 

 the case of neutron -gamma logging. 



Experiments, carried out on specimens of pure elements and rocks, have 

 shown that the intensity and the energy of the gamma rays spectrum, produced 

 by the initial inelastic collisions of neutrons mth atomic nuclei of various 

 rock -forming elements have characteristic features (^^). This is obvious in 



