Threshold voltage (Vth) and drain-source current (Ids) behaviour of nitride read only memories (NROM) were studied both in situ during irradiation or after irradiation with photons and ions. Vth 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 Ids with the total irradiation dose. A brief physical explanation is also provided.