Recently a sharp decrease in the radioactivity of tritium was reported, and a preliminary explanation of this effect was formulated in terms of a nuclear-pair hypothesis. Through the evaluation of several gas-solid exchange and diffusion experiments of others, where heavy radionuclides (65Zn, 63Ni, 85Sr) are used as tracers, it can be shown that such an effect may also exist for these nuclei. In all these experiments the second law of thermodynamics seems to be grossly violated. By pure formal application of the nuclear-pair hypothesis, all such deviations from normal behavior can be explained. Several straightforward experiments are proposed to prove the decrease in radioactivity of heavy nuclei.