An essentially new mechanism of eliminating the barrier in nuclear reactions of synthesis due to quantum‐mechanical averaging of paired and many‐body energy of interacting particles in microvoids in a solid is proposed. The results of calculations within the first order of perturbation theory indicate a complete ‘‘elimination’’ of the barrier in spherical microvoids of opticmal radiusRO&bartil;7.5 A˚. The same effect takes place in microslits with width LO&bartil;3 A˚. In structural inhomogeneities of both type with characteristic dimensions less than the optimal ones RO, LO, within the particles being condensed at the levels of quantized motion, as the concentration increases. An increasing pressure against the walls results in stretching the inhomogeneities up to the critical size, at which nonthreshold synthesis is realized. The characteristic time of the reaction realization in voids and slits has optimal size t∼10−5s.