ENVIRONMENT

Ionizing radiation and its doses

Radiation is present everywhere on the Earth. It is electromagnetic wave, that transmit the energy. Small amounts of energy are not harmful. To this group, light, TV, radio, communication radiation can be divided. Second group, it is radiation with much greater energy. It is high enough to knock out an electron from the orbit of the atom and form an ion. Ionization introduces changes in physicochemical properties of living cells, especially in deoxyribonucleic acid molecules (DNA). [19]

Ionizing radioactivity is an effect of continuous transformation of atoms. Disintegration occurs and some particles are emitted. But there are several types of radiation [19],[82],[104]:

  • Alpha radiation - heavy particles of helium nuclei with two neutrons and two protons. Large mass causes that ionizing ability is very high, but also leads to fast energy loss in the matter. Alpha radiation does not penetrate piece of paper of human body skin. It is dangerous only in direct contact with the radiation source or after reaching interior of human body. This type radiation comes from natural heavy particles such as thorium, plutonium, uranium but also from not natural transuranic elements.
  • Beta radiation - much smaller than alpha particles. They are electrons detached from atom nucleus. They can penetrate tissues to depth of 2 cm, and therefore are dangerous for skin. Serious influence on human health is considered after source inhalation or consumption. For protection layers of metal or plastic are sufficient.
  • Gamma radiation has a similar form to X-rays. Both are electromagnetic wave of high energy but gamma radiation is caused by nucleus disintegrations, X-rays not. It easily penetrates the matter, and thick layer of high density material is required to absorb radiation. Health danger level while exposure to gamma radiation is very high.
  • Neutron - particles emitted during fission reaction are not problem outside nuclear power plant. Thick, concrete layers absorb them.

    • It is necessary to measure the radiation. However single power of radiation in some case is not sufficient because it does not accord to human body effects or does not include type of radiation. Hence several factors are used to radiation description [19], [104] ,[105],:

  • The absorbed dose - measure that represents amount of energy absorbed in material (tissue, water, air etc.). The unit of measurement is the Grey (Gy), representing energy of one joule deposited in one kilogram of the matter.
  • The equivalent dose - includes different radiation effects, depending on radiation type. The absorbed dose is modified by "biological weighting factor". It allows to designate the equivalent dose from different radiation. The dose is increased by 20 times in case of alpha radiation or remains unchanged for example in case of gamma radiation. The unit is Sievert (Sv).
  • The effective dose - concerns risk of tissue damage depending on its type. This dose was introduced for purpose to determine overall radiation effect on human body, when radiation is received in different organs. Each part of body has unique correction factor. Multiplying equivalent dose by the factor and adding effects gives the comparable effective dose. The unit is Sievert (Sv).

    • Above units concern single doses or cumulative dose, but in many cases the concept of dose rate it used. It represents dose in relation to the exposure time, i.e. Sievert per hour (Sv/h) or Sievert per year (Sv/y).

    Radioactive materials and particles normally occurs in living environment. Thus, we are exposed to the harmful radiation. However its intensity is so low that it does not develop health effects according to [105]. Overall, annual, average dose to the population, according to [106] is 2,8 mSv. At about 85%, the source of radiation is natural, only at 25% radiation comes from man-made sources. Below, average example doses are presented [102], [107]:

  • Cosmic radiation - equivalent dose rate depends on latitude. In Poland it is 0,3 mSv/y. Dose at an altitude of 2000 m above sea level, is 0,6 mSv/y.
  • Earth radiation, depending on geological structure of the ground is between 0,5 - 50 mSv/y
  • Buildings made by brick, by reinforced concrete or prefabricated elements - 0,5 mSv/y
  • Human body - 0,2 mSv/y
  • Medicine - 0,5 mSv/y
  • Nuclear power plants - 0,00003 mSv/y overall, in the close distance it is 0,1 mSv/y

    • According to [105], small doses of radiation is not harmful and do not causes negative consequences for human body. Damaged cells are able to repair. However accurate threshold is not set. It depends on body strength. It is also not decided yet how large doses start to make irreversible changes in tissues. Nevertheless everyone agree that too high radiation causes cancer and may damage structure of DNA. In such situation cells can die after irradiation or can be improperly repaired. Then risk of cancer develops, cells lose their functionality or there are some genetic consequences in the next generations.[82]

    Table 12.Equivalent cumulative doses and their health effects
    Source: Own development based on

    J. K u b o w s k i "Nowoczesne elektrownie jadrowe", Warszawa, WNT 2010, [19]

    "Nuclear Energy Today", Nuclear Energy Agency. Organisation for economic co-operation and development. OECD Publications 2003,2005 [82]

    R. W a r r y, "Q&A: Health effects of radiation exposure", BBC News, 23 March 2011, http://www.bbc.co.uk/news/health-12722435, [108]
  • Copyrights 2011 © Michal Wierzbowski