  A bulk polycrystalline sample of YBa_{2}Cu_{3}O_{7-\delta} (\delta \approx
0.1) has been irradiated by \gamma-rays with ^{60}Co source. Non-monotonic
behavior of T_c (defined as the temperature at which normal resistance is
halved) with increasing irradiation dose \Phi (up to about 220 MR) is observed:
T_c decreases at low doses (\Phi \leq 50 MR) from initial value (\approx 93 K)
by about 2 K and then rises, forming minimum. At highest doses (\Phi \geq 120
MR) T_c goes down again. The temperature width, \delta T_c, of resistive
transition increases rather sharp with dose below 75 MR and somewhat drops at
higher dose. We believe that this effect is revealed for the first time at
\gamma-irradiation of high-T_c superconductor. The cross section for the
displacement of lattice atoms in YBCO by \gamma-rays due to the Compton process
were calculated, and possible dpa values were estimated. The results obtained
are discussed taking into account that the sample is granular superconductor
and, hence, the observed variations of superconducting properties should be
connected primarily with the influence of \gamma-rays on intergrain Josephson
coupling.
