  Irradiation with electrons is an efficient approach to inducing a large
number of defects with a minimal impact on the material itself. Analysis of the
energy transfer from an accelerated particle smashing into the crystal lattice
shows that only electrons with MeV energies produce point defects in the form
of interstitial ions and vacancies that form perfect scattering centers. Here,
we investigate the changes in the resistive characteristics of YBCO single
crystals from the 1-2-3 system after several steps of low-temperature
irradiation with $0.5-2.5$\,MeV electrons and irradiation doses of up to
$8.8\times10^{18}$\,cm$^{-2}$. The penetration depth of such electrons is much
larger than the crystal thickness. We reveal that defects appearing in
consequence of such electron irradiation not only increase the residual
resistance, but they affect the phonon spectrum of the system and lower the
superconducting transition temperature linearly with increase of the
irradiation dose. Furthermore, the irradiation-induced defects are distributed
non-uniformly, that manifests itself via a broadening of the superconducting
transition. Interestingly, the excess conductivity remains almost unaffected
after such electron irradiation.
