Cosmic rays and gamma ray emitters found in soil, construction materials, water, food, and the air are the principal sources of radiation that humans are exposed to. The primary external source of exposure to gamma radiation for humans comes from naturally occurring radionuclides, particularly when these processes are aided by other natural phenomena such aging deposition and wind erosion (Alaamer, 2008; Elles et. al., 1997). With or without his consent, man is exposed to ionizing radiation, which can result in damage and clinical symptoms such chromosomal changes, cancer induction, free radical generation, bone necrosis, and radiation carcinogenesis (Norman, 2008). Both high dosage and extended low dose exposure may result in damage and clinical signs. Ionizing radiation has a deadly effect, so it has been common practice to monitor and evaluate one's exposure levels and keep it as low as is practically possible (ALARA principle). The radioactivity in his environment, both natural and man-made, is referred to as the ambient radiation (Farai and Vincet, 2006). The bulk of lung cancer-related deaths are brought on by radon, one of the radionuclides present in the environment surrounding humans that delivers a substantial quantity of potentially deadly dosage (UNSCEAR 2000).
Radon, which makes up more than half of all natural source radiation, is the primary source of this radiation. In comparison to its other isotope, Rn − 220 (T1/2 = 50s), in the Th series, Rn − 222 (T1/2 = 3.82 days) in the U series builds up more readily in residences, making it relevant in terms of radiological health hazard. Ra − 226 (T1/2 = 1602 years), a radioactive noble gas that is a part of the U-238 series, undergoes alpha decay to produce radon. It comes from dirt and rocks, but it dissolves in water. The two primary ways that radon travels through soil are diffusion and advection, and its half-life of 3.82 days is long enough for it to diffuse into and accumulate in soil interstices. Radon is transported through soil interstices mostly by diffusion, and its half-life of 3.82 days is long enough for it to diffuse into and accumulate in dwellings. Radon is carried through soil by both diffusion and advection (Samuel et. al., 2022)
Release of radon from residue repository to the environment happen by the accompanying arrangement of procedures: (Moed, et. al., 1988, Yousif, et. al., 2017).
a. Production rate - This is said to be the soil gas radon concentration produced within the soil per unit time
$$a\left(Bq{m}^{-3}\right)={C}_{Rn}\times {\lambda }$$
1
Where; CRn is the radon concentration in the soil air in Bq/m3, λ is the radon decay rate of emanation (2.1E-6s-1).
b. Exhalation rate - which is the number of radon atoms that have been transported from the soil per unit surface area per unit time and then exhaled to the atmosphere. Radium concentrations in the soil, soil permeability and wetness, the condition of the vegetation cover, and weather conditions all affect how much radon is exhaled from the soil. The changes in radon activity in indoor spaces may be partially attributed to meteorological factors, way of life, and tenant habits (Gulan, 2017).
$$E\left(Bq{m}^{-2}{s}^{-1}\right)=a\sqrt{\frac{d}{{\lambda }}}$$
2
Where; d is the diffusion constant/coefficient (2.5E-6m2s-1), and a is the rate of production within the soil.
c. Emanation and transportation - Diffusion and adventive flow cause the movement of radon atoms formed from the decay of radium escape through the residue or soil profile to the ground surface.
Because of the potential health implications, radon levels in the environment are well known and regularly monitored in most regions of the world (Abumurad et al., 1997). On this element of our environmental health challenges, there are not that many data available in Nigeria. Therefore, research on radon concentration indoors and outdoors are required in places highlighted by a geological layer with a high potential for uranium 238. Additionally, the effective dose it contributes to society each year. The aim of this research is to measure outdoor and soil-gas radon concentration in estimating the annual effective dose, production and exhalation rate as well as well as establish a possible connection between them.
The established value of 9 nSv per (Bqhm− 3), used in previous UNSCEAR calculations, is still regarded as adequate for average effective dose estimates given the current range of values for the dose conversion factor. The following annual effective doses are calculated using the representative radon concentrations (CRn), equilibrium factors (F) of 0.6 outdoors, occupancy factors (O) of 1760 outdoor hours, and the dose coefficient previously mentioned (UNSCEAR, 1988; UNSCEAR, 2000)
Outdoor: AED(mSv/y) = CRn×Fout×Oout×DCF (3)
The reference level for outdoor radon recommended by International commission on Radiological Protection (ICRP) ranges from (100 to 300) Bqm− 3.
Study Area
The Basement Complex rocks surround the city of Abeokuta. These rocks, which date from the north-eastern region of Ogun state and range in age from Precambrian to early Palaeozoic, run southwestward and drop towards the coast (Akinse and Gbadebo, 2016). Between latitudes 7° 10 and 7° 15 N and longitudes 3° 17 and 3° 26 E, Abeokuta occupies a region of approximately 40.63 km2. The metamorphic rocks of the basement complex, which include granite, granitic gneiss, and pegmatite, are characterized by a variety of folds, structures with varying degrees of complexity, faults, and foliation. High background radiation levels and crystalline rock formations dominate the studied locations (Jibiri and Famodimu, 2013; Oni et al., 2014, Samuel et al., 2022).