Inferring the impact of environmental conditionings over natural gamma-radiation fluxes in a Brazilian tropical site

Natural gamma-radiation flux density at Earth’s surface is modulated by soil water retention capacity and the rainout/washout of short-lived radon progenies as major parameters. In this work, 11-year absorbed dose data from 36 TLD environmental stations, installed over different geological domains, allowed a better understanding of temporal and spatial variability of natural gamma-radiation, at a tropical region of Brazil. The results show conspicuous one-year cyclicity with increases during the winter-fall (dry season), varying from 3.9 to 14.1% compared to summer (wet season). TLD stations installed at beach sand terrains presented elevated coefficient of variation compared to results at soils and rocky terrains. This difference was attributed tentatively to changes in naturally occurring radionuclides activity concentrations in accordance with coastal sedimentary dynamics. Additionally, long-term TLD databases, selected from main geological domains, allowed the modeling of regional absorbed dose rates.

► We analyzed data of 36 TLD environmental stations during 11 years in Brazil.
► Markedly inter-annual variability with peaks during the winter-autumn season was observed.
► Combined soil water retention and radon exhalation modulate the gamma-radiation.
► TLD stations built at sand beach terrains tend to present highest variability.
► Absorbed dose rates were comparable to “lithological” estimates based on Th-U-K.