416 V. M. Zaporozhetz and E. M. Filippov 



silicon with an atomic w^eight of 29. In this case a gamma quanta source 

 of vip to 10^^ gamma quanta per second is necessary. 



3. Recognition of rocks containing rare elements with the atomic weight 

 of an order of 200 in a bore-hole section. 



In order to recognize the rare elements of such a high atomic weight 

 when their content in the rock varies from tenths to hundredths of one per cent 

 it is necessary to use a power source of an order of 10^° gamma c[uanta 

 per second. 



Scintillation neutron counters used in radioactive logging, besides the 

 neutrons, register also gamma quanta. Let us consider how the scattering of 

 the gamma ray will influence the results of gamma-neutron logging 

 in bombarding the deuterium of a water-oil contact. 



The effectiveness of the scintillation neutron indicators using the gamma 

 quanta with energy of an order of 1 MeV is approximately 100 times less 

 than their effectiveness in using neutrons. 



Let us assume that the generator produces a directed beam of gamma 

 quanta with an energy of 3 MeV. In reaction wth the electrons of the rock 

 atoms this radiation as a result of one act of scattering will lose an average 

 of 50 per cent of energy (^°), i.e. it will diminish to 1-1.5 MeV. By a proper 

 selection of the displacement potential in the network of the amplifiers 

 input cascade it is possible to succeed having the non-corresponding impulses 

 unrecorded by the registering instrument. However, owing to the great 

 power of the gamma quanta source there will be a certain number of correspond- 

 ing impulses which would influence the readings. If the source power is 

 4.6 X 10^2 gamma quanta per sec, and the resolution time of the electronic 

 device of the apparatus used in radioactive logging of an order of 10 /t/sec, 

 and the effectiveness of the recorder towards the gamma quanta is of an order 

 of 10~^, then the number of corresponding impulses is of an order of 

 10 X 10-6 X 10-5 x4.6 X 1012 _ 460 per sec. 



When the power of the gamma quanta source is 4.6 x 10^^ gamma quanta 

 per sec then m — 20. The speed of the photo -neutron count wll be equal 

 to 0.3 n/sec x20 = 6n/sec. Thus the influence of the synchronously 

 corresponding impulses of the scattered gamma radiation will considerably 

 exceed the effect measured by GNL. To surpass such an influence it is 

 necessary to increase the network displacement of the spectral input into 

 the amplifier so as to distinguish completely between the synchronously 

 corresponding impulses. Tlais is done by increasing the potential twice 

 in comparison with such as is necessary to suppress the non-corresponding 

 impulses. This leads to a slight, but only slight, diminution in the speed of 

 the neutron count. 



