400 



V. M. Zaporozhetz and E. M. Filippov 



Fig. 2 where there are shown the characteristic spectra of gamma rays pro- 

 duced during the irradiation of specimens of various elements by neutrons 

 with an energy of 14 MeV. There is also shown the background curve (8) ob- 

 tained in the absence of the scattering target. The study of hydrogen and 

 sulphur has revealed somewhat weak gamma rays with the corresponding 

 energies of 2.2 and 2.3 MeV. 



700 

 600 

 500 

 400 

 300 

 200 

 100 







20 40 60 80 100 



V 



i 



''^ 



e^ 



20 40 60 80 100 

 V 



Fig. 2. Differential spectra of the gamma radiation produced in inelastic collisions 

 of the neutrons with an energy of 14 MeV with the atomic nuclei of diverse substances. 

 1 — graphite; 2 — water; 3 — aluminium; 4 — magnesium; 5 — iron; 6 — calcium; 

 7 — silicon; 8 — background curve, obtained in the absence of the scattering agent. 



Of all the rock-forming elements only carbon (4.5 MeV) and oxygen 

 (6.5 MeV) produce considerable gamma radiation in inelastic collisions. 

 This allows us to anticipate the possibility of direct detection of carbon, and 

 consequently under favourable geological conditions of petroleum, with 

 the aid of the NGL method involving a neutron generator. 

 The capture of the fast neutrons occurs at the same time as their elastic and 

 inelastic scattering. Of a neutron with an energy of 14 MeV approximately 

 0.1 part is captured in collisions with nuclei, giving rise to radioactive 

 nuclei. 



Experiments with activation of rock specimens by fast neutrons have 

 shown that their radioactivity is connected with the formation of the radio- 

 active isotopes 0^^ (half-life of 27.5 sec and the gamma rays energy of 1.2 

 and 1.6 MeV), AP^ (half -life of 2.3 min and the gamma rays energy 1.8 

 and 2.3 MeV) and Na^* (half -life of 15 hr and the gamma rays energy of 1.4 

 and 2.76 MeV). Al is formed as a result of activation of silicon, Na of alumin- 



