Key words: Ionization microclimate, radioactivity, Becquerel, radionuclide, half-life, volume acitivty, electrostatic deposition

IONIZATION MICROCLIMATE

Ionization microclimate is a component of indoor environment formed by flows of ionizing radiation produced by radioactive substances of natural or artificial sources, which act on the individual and form one's overall condition. The ionizing radiation particles penetrate irradiated matter, breaks molecular bonds, and forms ions.

Radioactivity is the transformation of the core of an element into the core of another element, while releasing large amounts of energy in the form of invisible radiation (so-called radioactive radiation) that is dangerous to humans. There is natural and artificial radioactivity.

Radionuclide is a nuclide with an unstable nucleus whose atoms are subject to radioactive transformation together with the emission of ionizing radiation.

The basic physical quantity of ionization is the activity (Ak) of a given amount of radionuclide expressing the proportion of the mean number of radioactive changes and the time interval. The unit of activity is one decay per second or Becquerel (Bq). The activity of 1 Bq has a radioactive element characterized by one transformation per 1 second.

Volume activity is the quantity characterizing the number of radioactive conversions per unit of time in volume unit expressed in Bq/m³.

Half-life is the time taken for half the radionuclide's atoms to decay. The half-life is constant for the isotope of the given element. The half-life has values from a fraction of a second to millions of years. For example, the half-life of uranium ²³⁸U is 4.47 billion years old, half-life of radium ²²⁶Ra is 1602 years old and half-life of radon ²²²Rn is 3.82 days. Decay products are solids and are called daughters or progeny.

SOURCES OF IONIZING RADIATION

The source of ionizing radiation may be radioactive substances penetrating into the interior from the external environment, or substances occurring inside the building due to anthropogenic activities and the release of building materials and technological equipment containing radioactive material.

The most common sources of radioactive substances from the outside air are radioactive ash produced by thermal power plants, badly stripped subsoil of buildings in localities with the occurrence of radon in the subsoil, inappropriate building materials (blocks produced from fly ash) and landfills. Cigarette smoke, X-rays, or radioactive materials in laboratories are the most common sources of ionizing radiation in the interior of buildings.

OPTIMIZATION OF IONIZING RADIATION

Optimization of ionizing radiation can be ensured either by intervention into the source of radioactive material, or interference into the transmission field of ionizing radiation. Restriction or disposal of a source of radioactive material is the most effective way to optimize the indoor environment.

Intervention into the source can be performed by:

• Selecting a suitable building site (locality)
• limiting or preventing the penetration of radon into the building (antiradon measures)
• Choosing suitable building materials (certified materials and products)

Interferences into the transmission involves:

• Restricting the spread of radioactive substances in the building
• Ventilation and air filtration
• Surface deposition, i.e. sedimentation of radioactive substances
• Electrostatic deposition

The limitation of the spread of radioactive substances in the building can be achieved by design-layout modifications of the building such as dividing vertical shafts into smaller sections, appropriately transferring sources of radioactive material in the building, or applying differential ventilation. The spread of ionizing radiation is a problem especially in multi-storey buildings, When the radioactive material is propagated by thermal buoyancy. Continuous stairs along the height of the building without interruption can be a source of intense spread of radioactive gases throughout the building.

In addition to ensuring adequate air exchange, it is advisable to design pressure zones between spaces according to the degree of their contamination (contamination). The largest negative pressure is chosen for areas with the highest contamination. Air recirculation is not included in such areas. Reducing the dose of fresh air in order to reduce the energy performance of a building can result in an increased concentration of radioactive substances in the building.

Filters can reduce the spread of radioactive substances bound to some kind of aerosol. There are two types of filters - cassette or electrostatic:

• Cassette filters are boxes with a filter cartridge. Filter cartridges are not washable, but they are replaced with new ones (low acquisition costs, but higher operating costs)
• Electrostatic filters do not increase overall system pressure over time (like other filters). Captured particles can be washed with water (high cost of ownership, cheap operation).

Electrostatic deposition operates on the principle of artificially created electrostatic field. Electrically charged particles settle on electrodes of opposite polarities.