Threshold voltage V_th and drain-source current I_DS behaviour of nitride read only memories (NROM) were studied both in situ during irradiation or after irradiation with photons and ions. V_th loss fluctuations are well explained by the same Weibull statistics regardless of the irradiation species and total dose. Results of drain current measurements in-situ during irradiation with photons and ions reveal a step-like increase of I_DS with the total irradiation dose. A brief physical explanation is also provided.