Abstract: The seawater radioactivity sensor developed based on NaI(Tl) scintillation crystal detection method is the main technological means to carry out in situ automatic monitoring of marine radionuclides at home and abroad. Nevertheless, when the seawater radioactivity sensor is continuously operating at sea for a long time, the measured seawater gamma spectrum data will drift due to the influence of ambient temperature. In this paper, the seawater radioactivity sensor measurement experiment is carried out under the condition of environmental temperature gradient change, and the drift law of the gamma spectrum data calculated by the seawater radioactivity sensor which occurs with the environmental temperature change is analyzed. When the ambient temperature is lower than 15 ℃, channel address corresponding to the characteristic energy peak increases with the increase of temperature; on the contrary, when the ambient temperature is higher than 15 ℃, the channel address corresponding to the characteristic energy peak decreases with the increase of temperature. The gamma spectrum peak channel address shift can be expressed as a quadratic function of temperature, and further a correction method of gamma spectrum shift based on ambient temperature change is proposed. It is verified by laboratory experiments on air and water environment that the peak channel address drift of characteristic peak after air environment correction is not more than ±2 channels, and the peak channel address drift after water environment correction is not more than ±3 channels, which meets the requirements of temperature drift correction for continuous measurement of gamma spectrum by the sensor.

Key words: sea water radioactivity sensor, temperature drift, spectrum correction