Biological effects of ionizing radiation

Classification of radiation sources

According to the Radiation Safety Standards (NRB-99), all sources affecting the population are divided into two main groups:

1. Natural sources. These include cosmic radiation and natural radionuclides originally present in the environment (water, air, soil, and food). They contribute the maximum to the human radiation burden.
2. Artificial sources. These are subdivided into two subcategories:
3. Medical procedures (diagnostics and radiotherapy).
4. Technogenic sources (artificial radionuclides, ionizing radiation generators, and natural radionuclides specifically concentrated as a result of human activity).

Technologically altered radiation background

Human activity can alter the natural radiation background. The technologically altered natural radiation background is formed primarily due to the following factors:

• Road and civil construction. The erection of buildings and highways involves natural materials (crushed stone, gravel, sand) that possess their own radioactivity.
• Agriculture. The use of artificial phosphate fertilizers containing isotopes of the thorium and uranium series creates an additional burden. Workers are exposed to external radiation from fertilized soils, as well as internal exposure via inhalation of soil dust and the alimentary route (ingestion of foods grown on these soils). The effective equivalent dose from fertilizers is 14 × 10⁻⁵ mSv/year.

Internal exposure and the impact of building materials

Building structures can play a dual role: they shield external radiation while themselves acting as sources of internal exposure. Artificial materials (concrete, brick made from sand and clay) accumulate radiation more strongly than natural ones (wood).

Compared to open areas, buildings alter the radiation dose as follows:

• Wooden houses: dose increase by 2 times (in living rooms) and 7 times (in basements).
• Brick buildings: dose increase by 10 times (in rooms) and 40–100 times (in basements).

In enclosed spaces, the main source of exposure is the radioactive gas radon and its decay product thoron. They are formed from radium-226, uranium-238, and thorium-232 present in walls and foundations. The average radon content in indoor air reaches 35 mBq/L (the thoron content is 2 orders of magnitude lower). The concentration of these gases depends on the amount of radium in the walls, the quality of ventilation, and the nature of the wall coating, which affects emanation and sorption processes.

Regulation and dose limits (NRB-99)

Radiation safety is ensured by compliance with exposure quotas, radiation monitoring, and sanitary legislation. For natural sources, no total limit is established; instead, the activity of specific media is regulated (radon in air, radionuclides in building materials, food, and water).

For technogenic sources under normal operating conditions, strict dose limits (DL) apply. All individuals are divided into three categories:

• Personnel (Group A): work directly with sources.
• Personnel (Group B): are in the area of influence of sources due to working conditions.
• Public.

(Note: the effective dose is averaged over any consecutive 5 years). These standards are mandatory.

Class and exam questions

What else to study on this topic

• Mechanisms of emanation and sorption of radioactive gases (radon and thoron) by indoor wall coatings.
• The role of radium-226, uranium-238, and thorium-232 in the formation of the Earth's natural radiation background.
• The impact of ventilation regimens on reducing radon concentrations in work area air.
• Criteria for the sanitary assessment of specific activity in building materials (slag, rubble stone, sand).
• Principles of calculating equivalent dose for various human tissues (lens, skin, hands, feet).

Other topics in "Chapter 7. Basics of radiation hygiene"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.