Simulation of the shielding properties of environmental components against the external radioactive radiation from the Ordovician Dictyonema shale

Abstract

This paper presents the results of simulating the conditions of absorption of natural radionuclides (uranium-238, thorium-232, potassium-40) in different environment media (water and quartz sand) to assess the effect of the shielding properties of environmental components on the intensity of external radiation exposure to the benthic biota. The source of radiation was the lower Tremadocian Dictyonema shale, which formed the bottom of the Baltic Paleobasin. Water and quartz sand, which was gradually deposited on the roof of the Dictyonema shale, were used in the simulation as media (materials) absorbing the primary radiation. The manuscript shows an experiment conducted in full-scale conditions considering a single exposure of a section of Ordovician rocks that includes highly radioactive Dictyonema shale. This is a small area, but the simulation results are also valid for larger areas as the Baltic Paleobasin. During the late Tremadocian -Floian, along with transgression, benthic biota began to emerge. The experiment shows quantitatively what dosage this biota could have experienced over tens and hundreds of thousands of years, until the Dictyonema shale was covered with a sufficiently thick layer of water-flooded sediments. Experimental data show that the presence of a 10 cm thick layer of water reaches absorption of 40 % of the integral flux of all gamma lines of natural radionuclides (NRN), and in a moist quartz sand layer of the same thickness the absorption value does not exceed 50 %. Thus, despite the screening effect of the environment, the benthic biota of Baltoscandia in the Early Ordovician could have been under significant radiation exposure for millennia. The main value of the experiment is that it was performed in situ, and exclusively natural media were used as modelling elements.

Studies of Natural Soil Radioactivity in the Kirchhoff Hill (the Leningrad Region, the Russian Federation)

“…The amplitude of the upheaval of the overlying bed of the Siverskiy clays of the Cambrian period and overlying rocks reaches 100 m. What calls attention to itself is the strong erosion of clays and compartmentalization of limestones. The thickness of quaternary deposits in this region usually does not exceed several meters, while here it reaches 80 m [1,2].…”

“…From the geoecological point of view, a special place in the geological section of the Kirchhoff Hill is occupied by the dictyonema oil shales, the thickness of which reaches 3.5 meters. These are highly radioactive geological bodies that determine the radiation situation in the Leningrad Region along the entire length of the Balto-Ladoga clint [1,2].…”

“…The modern period of soil formation on the territory of the Leningrad Region started after the melting of the ice sheet about 12 thousand years ago [1]. As a result of glacial tectonic dislocations and due to numerous local elevations and depressions of the relief, dictyonema oil shales in the area of the Kirchhoff Hill can contact directly with the soil over relatively large areas [4,5].…”

“…In [3], if the results of gamma survey reveal zones in which the dose rate of gamma radiation exceeds 0.3 mcSv/h on land plots for the construction of residential and public buildings, or 0.6 mcSv/h on land plots for the construction of industrial buildings and structures, then such zones should be considered as anomalous. It should be noted that the value of the equivalent dose rate of 0.3 mcSv/h for gamma radiation corresponds to the exposure dose rate of 31 mcR/h, and that of 0.6 mcSv/h -to the exposure dose rate of 62 mcR/h [1,2]. Therefore, when developing a map of the gamma field for the delineation of the anomalous zones, we selected precisely these boundaries of the classification intervals -31 and 62 mcR/h.…”

Assessment of the level of soil pollution of agricultural lands Kotlin Island

“…It follows from the data obtained that, under conditions of relatively high soil contamination with heavy metals, most of the metals intensively come from the soil, but at the same time they accumulate mainly in the roots rather than in the aerial parts of plants [51][52][53][54][55][56][57][58]. In this case, soil cleaning does not occur.…”