  The $(n,\alpha)$ reactions play an important role for the energy generation
and the synthesis of chemical elements in the stars, as well as for nuclear
engineering and medical applications. The aim of this study is to explore the
evolution of $(n,\alpha)$ reactions in Fe and Sn isotope chains in order to
assess their properties with the increase of neutrons in target nucleus, and
compare with other relevant neutron induced reactions. Model calculations of
the cross sections are based on the statistical Hauser-Feshbach model in TALYS
implementation, using global optical model potential that is additionally
adjusted by the $(n,\alpha)$ cross section data for $^{54}$Fe and $^{118}$Sn.
The calculations of $(n,\alpha)$ reactions in Fe and Sn isotopes provide the
insight into their isospin dependence and properties over the complete relevant
range of neutron energies. The results show the evolution of the cross sections
with pronounced maxima at low-mass isotopes, and rather strong decrease for
neutron-rich nuclei consistent with the reduction of the reaction $Q$-value and
increased contributions from other exit channels from compound nucleus. The
analysis of the Maxwellian averaged cross sections at temperatures in stellar
environment shows that while the $(n,\alpha)$ reactions contribute for the
low-mass isotopes, in neutron induced reactions with nuclei with neutron
excess, $\gamma$ and neutron emission dominate.
