  Exothermal nuclear reactions which become forbidden due to Coulomb repulsion
in the\ $\varepsilon \rightarrow 0$ limit ($\lim_{\varepsilon \rightarrow
0}\sigma \left( \varepsilon \right) =0$) are investigated. ($\sigma \left(
\varepsilon \right) $ is the cross section and $\varepsilon $ is the center of
mass energy.) It is found that any perturbation may mix states with small but
finite amplitude to the initial state resulting finite cross section (and rate)
of the originally forbidden nuclear reaction in the $% \varepsilon \rightarrow
0$ limit. The statement is illustrated by modification of nuclear reactions due
to impurities in a gas mix of atomic state. The change of the wavefunction of
reacting particles in nuclear range due to their Coulomb interaction with
impurity is determined using standard time independent perturbation calculation
of quantum mechanics. As an example, cross section, rate and power densities of
impurity assisted nuclear $pd$ reaction are numerically calculated. With the
aid of astrophysical factors cross section and power densities of the impurity
assisted $d(d,n)_{2}^{3}He$, $d(d,p)t$, $d(t,n)_{2}^{4}He$, $%
_{2}^{3}He(d,p)_{2}^{4}He$, $_{3}^{6}Li(p,\alpha )_{2}^{3}He$, $%
_{3}^{6}Li(d,\alpha )_{2}^{4}He$, $_{3}^{7}Li(p,\alpha )_{2}^{4}He$, $%
_{4}^{9}Be(p,\alpha )_{3}^{6}Li$, $_{4}^{9}Be(p,d)_{4}^{8}Be$, $%
_{4}^{9}Be(\alpha ,n)_{6}^{12}C$, $_{5}^{10}B(p,\alpha )_{4}^{7}Be$ and $%
_{5}^{11}B(p,\alpha )_{4}^{8}Be$ reactions are also given. The affect of gas
mix-wall interaction on the process is considered too.
