EXPOSURE TO RADON
The man is anywhere and always exposed to natural radiation, in particular, radioactive gas RADON.
RADON is an inert natural radioactive gas (half-life is 3.8 days) without smell, color and taste. It results from natural radioactive decay of radium (uranium radioactive family) in Earth’s depths, is accumulated in rocks and groundwater, and then is gradually transferred to Earth’s surface through cracks and with water.
RADON is easily released from ground to the air. Its decay is accompanied by alpha emission and formation of daughter products, being alpha emitters as well. Sticking to microscopic dust, alpha particles form a radioactive aerosol in the air.
RADON activity concentration in the atmosphere is usually very low and increases sharply when RADON enters closed airspace where it accumulates. Since RADON is almost 7.5 times heavier than air, its activity concentration is generally higher in basements and other premises located in the ground and on the surface.
According to the World Health Organization (WHO), RADON is the second most significant cause of lung cancer in many countries. Depending on the average level, its contribution to all human lung cancer cases varies from 3% to 14%.
RADON target is the bronchus: a pulmonary system, in particular, cells of the epithelial tissue of lung walls.
When radioactive aerosol is inhaled, alpha particles are deposited in the respiratory tract and may cause lung cancer.
Lung cancer develops over a long period from 15 to 40 years.
The risk of lung cancer caused by RADON depends on:
• RADON activity concentration;
• duration of its impact;
• individual liability for development of this disease.
Under a combined impact of RADON, its decay daughter products, and a number of non-radiation factors (dust, exhaust gases, tobacco combustion products, etc.) on the human body, adverse effects are increasing.
The risk of lung cancer from exposure to RADON for smokers is an order of magnitude higher: most (almost 90%) of patients with lung cancer associated with exposure to RADON are smokers.
Combined with tobacco smoke, the oncogenic effect of RADON and its decay daughter products increases by two to ten times and reduces the latent period of lung cancer.
According to epidemiological studies of the last decade, the risk of cancer (probability of pulmonary oncological diseases) increases on the average by 10% under chronic exposure for 30 years for each additional 100 Bq/m³ and depends directly on the average level of RADON activity concentration in the air.
Children are the critical group of people regarding exposure to RADON.
Doses to children are conditioned by:
• smaller size of the child’s body and organs, in particular, lungs (dose received depends on their area and volume of pulmonary ventilation);
• metabolism peculiarities (growing organism);
• greater radiosensitivity of organs and systems of the child’s body.
Children receive the maximum exposure dose when they are about six years old. The relative risk of developing lung cancer due to exposure to RADON for children under 10–14 years is higher than for adults (by approximately 1.5–3 times).
MEASUREMENT UNITS AND REGULATED VALUES FOR RADON ACTIVITY
RADON activity concentration is measured as the number of radon nucleus decays per second in one cubic meter of the air. One decay per second corresponds to one becquerel (Bq). Accordingly, the activity concentration of this isotope is determined in becquerels per cubic meter (Bq/m³).
In compliance with the Radiation Safety Standards of Ukraine, the regulated value is the average annual equivalent activity concentration of RADON in the air of rooms and should not exceed:
• 50 Bq/m³ for new and reconstructed buildings, as well as for child-care centers, health resorts, and health improvement establishments;
• 100 Bq/m³ for buildings in operation.
RADON IN HOUSES
The strongest impact of RADON is experienced by a person who is in a closed, non-ventilated room, since it is known that people commonly spend 80% of their time in buildings (houses).
RADON sources in buildings:
• soil under the building foundation and near it;
• building materials and fencing structures (walls, foundation, partitions);
• internal water supply system of the building (especially artesian holes and wells).
1. Floor gaps
2. Masonry gaps
3. Ventilation system
4. Supply lines
FLUCTUATIONS OF RADON ACTIVITY
RADON activity concentration changes with time (Figs. 1 and 2).
Fig. 1. Daily fluctuations of RADON activity in room air
Fig. 2. Monthly fluctuations of RADON activity in room air
RADON activity concentration in buildings depends on:
• engineering and planning features and characteristics of the building;
• room ventilation mode (determines daily fluctuations, see Fig. 1);
• lifestyle of inhabitants;
• weather and climatic conditions (causing seasonal and mid-month fluctuations, see Fig. 2).
WAYS FOR DECREASING RADON ACTIVITY CONCENTRATION
In winter, RADON activity concentration is, as a rule, much higher than in summer because of tightly closed windows and doors, reducing indoor ventilation (air exchange).
RADON activity concentration may differ even in adjacent identical buildings and may change every day or every hour in the same building.
In view of such fluctuations, in order to determine the average annual level of RADON activity concentration in the air, it should be measured over a long period of time (not less than a month).
WAYS FOR DECREASING RADON ACTIVITY CONCENTRATION
RADON activity concentration in the building may be decreased in the following way:
• regular ventilation of rooms, especially the basements;
• sealing of floor gaps;
• isolation of space under the floor from the ground (concrete pouring);
• installation of special devices to remove RADON from rooms.
DEVICES TO MEASURE RADON ACTIVITY
Radon accumulators (detectors) are used to measure RADON activity concentration (Fig. 3). These devices are installed in the rooms where inhabitants stay for the longest period (bedrooms, children’s rooms). After the exposure period (not less than 30 days), radon accumulators are sent to a measuring laboratory where film detectors are chemically treated. Then the tracks (traces of damage) on the detector left by alpha particles emitted by radon are calculated using a measuring device (Fig. 4). RADON activity concentration is calculated by the number of such tracks.
Fig. 3. Radon Accumulator
Fig. 4. Measurement Instrument
The booklet has been developed by the team of authors: T.A. Pavlenko, ScD in Biological Sciences, M. A. Frizyuk, PhD in Biological Sciences, N. V. Aksenov, PhD in Biological Sciences, and O. A. German under financial support of the Swedish Radiation Safety Authority (SSM). Translation: Uatom.org Editorial Board.