FIELD: determining moderation length of fast neutrons. SUBSTANCE: method involves irradiation of medium being analyzed by stationary neutron flux and recording of flux of epithermal neutrons Net at recorded distance from neutron source followed by calculation of moderation length L using experimentally derived equation including well diameter. In addition, epithermal neutron flux is measured by means of same instrument in well fluid; measurements are also made of rock clayness Kcl and density ρ their values being used to distinguish hydrogen containing and non-containing strata. Mathematical models for hydrogen containing and non-containing strata are used to calculate moderation length of fast neutrons in rock. Prior to analyzing unknown media Net is measured in standard media with known moderation lengths and well diameter, and measurement data are used to calculate constants for mathematical models. EFFECT: improved neutron moderation length measurement accuracy. 4 cl, 1 tbl
