  A single crystal of isovalently substituted Ba(Fe$_{1-x}$Ru$_{x}$)$_2$As$_2$
($x=0.24$) was sequentially irradiated with 2.5 MeV electrons up to a maximum
dose of $2.1 \times 10^{19}$ electrons/cm^2. The electrical resistivity was
measured \textit{in - situ} at $T=$22 K during the irradiation and \textit{ex -
situ} as a function of temperature between subsequent irradiation runs. Upon
irradiation, the superconducting transition temperature, $T_c$, decreases and
the residual resistivity, $\rho_0$, increases. We find that electron
irradiation leads to the fastest suppression of $T_c$ compared to other types
of artificially introduced disorder, probably due to the strong short-range
potential of the point-like irradiation defects. A more detailed analysis
within a multiband scenario with variable scattering potential strength shows
that the observed $T_c$ vs. $\rho_0$ is fully compatible with $s_\pm$ pairing,
in contrast to earlier claims that this model leads to a too rapid a
suppression of $T_c$ with scattering.
