An estimate of the cross sections of nuclear reactions with thermal neutrons in terms of the average parameters of the target nucleus (the strength function, the average level spacing, and the average reaction width) is obtained. The probability distributions for the ratios of actual thermal neutron cross sections to their estimated values are introduced. These functions can be calculated from the statistical model. They are calculated for neutron radiative capture and for inelastic neutron acceleration by the isomeric nuclei (as weell as the (n,α) reaction, etc.). Using these results, one can predict the probability of finding the actual thermal neutron cross section in a given interval.Download: pdf (860K), OCR'ed pdf (2280K).