**1. Introduction**

Radon is the most contributing source of ionizing radiation to human beings, in the atmosphere. It is a colorless, invisible, undetectable gas to human senses that causes lung cancer especially in areas where it is abundant. Areas of high levels of radon include underground uranium mines and locations close to mine tailings of which its buildings are non-ventilated. Lubin et al. [1] state that about 40% of deaths in mine workers are linked to the radon emanation in underground mines, in United States, radon is the second most contributing source to deaths due to lung cancer [2]. The International Commission on Radiological Protection recommends that the radon concentration level in dwellings should not exceed 300 Bq/m3 [3]. In South Africa, radon from areas of possible high radon emanation is a concern due to the history of mining, disposal of uranium tailing, use of mine waste for building materials [4]. Areas of high radon emanation include:


Mitigation strategies to reduce radon to acceptable levels to the public and mine workers are of necessity for implementation. Strategies such as reducing radon levels in underground mines by ventilation systems, reducing radon emanation in tailing dams by pouring 2 m of clay and topsoil to trap radon, and identifying radon entry points for sealing in houses or mines. To evaluate the effectiveness of the mitigation system to reduce radon to ensure safe public health, a properly calibrated radon detection device is necessary to ensure accurate exposure levels of radon in workplaces and houses [5]. With a calibrated radon detector, results of measurement before and after application of a mitigation system will absolutely indicate the rate of reduction of radon emanation. Therefore, buildings can be fixed if high radon emanations are detected, shortening the statistics of lung cancer deaths due to excessive exposure to radon.

The most common method of calibrating the radon detectors is exposing them to a steady flow of radon concentration from a standard radon source in an airtight radon chamber, under controlled environmental parameters [6]. A facility to calibrate radon detectors in a designed radon chamber at the Centre of Applied Radiation Science and Technology is in development phase.

In the following subsections, radon radiological properties, its transport behavior in the environment, and mitigation system will be introduced.

#### **1.1 Radon radiological properties**

222Rn is a noble radioactive isotope of atomic number 86, and it originates from the decay chain of 238 U as one of its decay product, 226Ra transforms into 222Rn by alpha particle emission as seen in **Figure 1**.

Radon alpha particles travel a distance of 4–7 cm with an energy of 5.5 MeV. Alpha particles' energy from radon daughter nuclei is more than that of radon, the parent. Polonium (218Po) with half-life of 3.05 minutes has energy of 6.0 MeV, while polonium (214Po) has 7.7 MeV. Hence, radon daughter nuclei are dangerous and pose health risk in an enclosed space such as offices and houses.

#### **1.2 Transport of radon in the environment**

Radon is found in rocks and soils, and its abundance in the environments depends on moisture, porosity, and the activity of uranium and radium in soils and rocks. The concentration of radon in soil differs due to the concentration of its parent radionuclide and the ability of the soil to emanate radon.

Factors that affect the mobility of radon in the soil include porosity, moisture content of soil, and permeability. Hosoda [8] found that the moisture content of soil in the range of 0–8% in a rectangular volume of 2840 cm3 increases radon emanation but, moisture content that is above 8% decreases radon emanation. Permeability of soil such as gravel and sand allows the transport of radon gas from several depths in the ground as seen in **Figure 2**. Impermeable soil such as clay and silt has low porosity, and therefore, the transport of radon is small. Decreased levels of radon in clays are due to the amount of water content in them, but in the dry clays with cracks, radon migration is more in non-cracked clay [10, 11].

Rocks with varying degrees of radium activity content are the source of radon in groundwater. The measure of 222Rn activity differs from surface water of lakes or rivers, as radon in underground water is not mobile as in the surface of the surface of the *An Overview of Radon Emanation Measurement System for South African Communities DOI: http://dx.doi.org/10.5772/intechopen.109065*

#### **Figure 1.**

*The emission of radon from radium in underground rocks or soil to water [7].*

#### **Figure 2.**

*Permeability of soil from underground to surface soil [9].*

earth. Methods of obtaining water from underneath the earth in wells or boreholes disperse high levels of radon to the atmosphere [12]. **Figure 3** illustrates the dispersion of radon from rocks to water.

**Figure 3.** *Migration of radon in underground radium rocks to water [7].*
