Interrelations between superconducting properties and defect evolution in neutron irradiated YBa$_{2}$Cu$_{3}$O$_{7}$.

We investigated the effect of neutron irradiation on the electric and magnetic properties, including the enhancement of the critical current density, of ceramic YBa$_{2}$Cu$_{3}$O$_{7}$(LiF)$_{x}$ samples. The superconducting properties of the virgin samples reach the optimal values for $x$ = 0.04. Up to the same $x$ value, the neutron irradiation up to 5$\times $10$^{17}$ neutrons/cm$^{2}$ enhances the superconducting response (critical temperature, transition width, etc) and double up the magnetic irreversibility. For $x \ge $ 0.08, all the superconducting properties are depressed whereas the increase of the irreversible magnetization is still present but less spectacular. The analysis of this behavior suggests a self-organization of the defects at low LiF content while for $x \ge $ 0.08 they are uniformly distributed within sample.