Abstract: This article discuses the application of anti-cosmic ray γ spectrometer with low background level on water sample measurement. In this paper, a water standard source is used to efficiency calibration, and the difference of detection efficiency of water samples of different shapes is compared. The detection limit of the water samples measured by the anti-cosmic ray γ spectrometer is compared with other gamma spectrometers. Results when γ energy E<130 keV, the detection efficiency of marlin cup ($\phi$ 17 cm×H17 cm) is lower than the cylinder ($\phi$7.0 cm×7.5 cm) for water samples. When E>130 keV, the detection efficiency of marlin cup is higher than the cylinder sample. The detection limit of marlin cup measured by anti-cosmic γ spectrometer was one magnitude lower than that of cylinder water samples. The detection limit of the anti-cosmic γ spectrometer for the same water sample is one magnitude lower than that of the common γ spectrometer. The detection limit of radionuclides such as ¹⁴⁴Ce, ¹³⁷Cs and ⁶⁰Co in the samples of marlin cup water without pretreatment is 3.07×10^-2 Bq/L, 3.67×10^-3 Bq/L and 3.7×10^-3 Bq/L, directly measured by anti-cosmic γ spectrometer. Conclusion the anti-cosmic γ spectrometer can be used for the measurement of water samples with low radioactivity. Its advantage is that it can reduce pretreatment time, shorten sample measurement cycle, greatly reduce detection limit and improve measurement accuracy.

Key words: anti-cosmic ray γ spectrometer, anti-coincidence, water sample measurement