Abstract
A new method for simulation of nuclear γ cascades by the Monte Carlo technique is described. It makes it possible to generate artificially individual events of the γ-cascade decay of neutron capturing states in heavy nuclei. For the purpose of determination of lifetimes of nuclear levels by the GRID method the previously developed Mean Free Path Approach for modelling atomic collisions and their interplay with cascades has been generalized. Examples of the use of this generalization for determination of lifetimes of selected (150)Sm and (158)Gd levels are given and discussed.