  The probability of the events that the final states are detected with or
interact with the nucleus in a finite time interval T was found to be, $P=\text
T \Gamma_0 +P^{(d)}$. $\Gamma_0$ is computed with Fermi's golden rule, and does
not depend on the nuclear wave functions. $P^{(d)}$ is not given by Fermi's
golden rule, and depends on the nuclear wave functions. In the electron mode of
pion decays, $\Gamma_0$ is proportional to $m_e^2$ but $P^{(d)}$ for the event
that the neutrino is detected is proportional to $m_{\nu}^{-2}$. $P^{(d)}$ does
not hold the helicity suppression satisfied in $\Gamma_0$ and is inevitable in
non-stationary quantum phenomena.
