Permanence limits of the radioactive decay constant in the case of electron capture

The role of different factors is investigated which affects relative change Δlambda/lambda of the radioactive decay constant lambda in the case of electron capture. It is shown that an essential contribution to Δlambda/lambda may be provided by a change of all the factors entering the expression for lambda (neutrino momentum, the numbers characterising the electron subshell population, the Coulomb amplitudes of electron radial wave functions, correction factors accounting for exchange and overlap effects in electron capture). A relatiVe weight of each factor depends on the nucleus charge Z and the total transition energy. A comparison of the theory with the experiment makes it possible to conclude that lambda are the same with an accuracy of approximately 10-3 for medium nuclei (20 <= Z <= 55) and approximately 10-4 for heavy ones (55 <= Z <= 94) in different chemical compounds with some variation of this accuracy for particular chemical elements