Deep level spectroscopy in neutron irradiated FZ and MCz Si was performed by extrinsic photoconductivity spectra measurements in the range of temperature of 18-120 K. The lukovsky model was used, and the Gaussian distribution of deep level energy demonstrated the best fit of simulation and experimental data. The nonmonotonous change of deep levels during annealing, and non-monotonous dependence of their concentration on the fluence were observed. The photoconductivity decay was investigated by the transient photo-Hall effect, recombination parameters of the main recombination centre were determined, and the recombination centre model was proposed. The photoconductivity and thermally stimulated current measurements were used to demonstrate the existence of photogeneration of free carriers by a cascade of optical and thermal transitions.