This paper presents a measurement of defects in the silicon detector, which is made of high resistivity N type material. The detector was irradiated in a nuclear reactor with a high neutron flux. Then, created defects in detector were identified by deep-level transient spectroscopy (DLTS) measurement. DLTS measurement was done on DL4600 BioRad measuring apparatus. The detector was irradiated with a total flux of 7,63.1015 n/cm-2. Immediately after irradiation the detector did not show diode characteristics. However, after detector annealing at 400C for 10 minutes it became possible to carry out DLTS measurement at reverse bias. The DLTS spectra are compared with similar already published results obtained within RD50 collaboration.