Nationwide mapping of terrestrial gamma radiation in South Korea using a car-borne survey system

This study conducted a nationwide car-borne radiation survey to assess background radiation levels originating from naturally occurring radionuclides across South Korea. Two survey vehicles were developed, each equipped with NaI(Tl) detectors and high-pressure ionization chambers (HPICs), and deployed over a period of approximately four years. As a result, a total of 723,052 gamma-ray spectra and ambient dose rate measurements were collected. A post-processing tool incorporating an automatic peak-channel tracking algorithm and net count rate (CPS) calculation was developed to extract radionuclide-specific net count rates. These values, along with the dose rates, were converted into concentrations of equivalent uranium (eU), equivalent thorium (eTh), and potassium-40 (⁴⁰K) as well as corrected ambient dose rates, using established conversion factors and shielding correction models from previous studies. The resulting geospatial database contains activity concentrations in soil and ambient gamma dose rates at each measurement points. The average concentrations were 51.2 Bq kg^-1 for eU (range: 0.003-927 Bq kg^-1), 58.9 Bq kg^-1 for eTh (range: 0.02-556 Bq kg^-1), and 877 Bq kg^-1 for ⁴⁰K (range: 21-3,135 Bq kg^-1), with an average dose rate of 131 nSv h^-1. The uncertainties represent standard deviations (k = 1). Four distribution maps were produced to visualize the spatial distribution of terrestrial radiation. The comprehensive and high-resolution data obtained through this study provide a quantitative foundation for assessing public radiation exposure and for informing national policy on the management of existing exposure situations.