Development and field application of a vehicle-mounted NaI(Tl) gamma spectrometer for rapid mapping of 226Ra, 232Th and 40K in agricultural soils

In agricultural soil radioactivity research, the specific activities of radionuclides such as 226 Ra, 232 Th and 40 K are mainly analyzed in laboratories after sampling, which is time-consuming and costly, making it unsuitable for large-scale agricultural applications. This paper establishes a mathematical model correlating soil radionuclide specific activity with gamma-ray intensity for on-site rapid detection of soil radioactivity. Based on MCNP simulation calculations, a vehicle-mounted soil gamma spectrometer was developed using a NaI(Tl) detector with dimensions of 5 × 10 × 40 cm. After calibration, the instrument, mounted on the rear of an agricultural machine, can detect the content of radioactive elements in the soil during plowing. It features real-time positioning and display of radionuclide specific activity, with the ability to measure up to 88,089 m 2 per hour. The instrument was applied in a 264,267 m 2 experimental field, and the distribution maps of the specific activities of 226 Ra, 232 Th and 40 K in the experimental field were obtained. Compared with laboratory analysis results, the relative deviations of the specific activities of 226 Ra, 232 Th and 40 K measured by the vehicle-mounted soil gamma spectrometer were within ±16%, ±15%, and ±10%, respectively. This device can enhance the operational efficiency in measuring the specific activity of soil radionuclides and reduce the cost of investigations into the distribution of radioactivity in agricultural soil.