What is Radioactivity

Radioactivity represents natural or artificially caused change of atom nucleus accompanied with emission of radioactive radiation. Artificial radioactivity is disintegration of atom nucleus (nuclide) activated by artificial submission of energy to nucleus in such a way that it becomes unstable and it disintegrates usually into two smaller nuclei with simultaneous emission of radiation alpha, beta or gamma. Vice versa, natural radioactivity is a spontaneous disintegration of radionuclides.

Natural radioactivity of ground, atmosphere, water and omnipresent cosmic radiation are parts of our environment and it forms the natural radioactive background. We are also exhibited to artificial ionizing radiation - from television screens, from medical devices, radioactivity released by industrial utilization of radioactive materials. It is necessary to protect ourselves against every excessive radioactive radiation, which holds true for all its sources starting from medical ones up to nuclear reactors in nuclear power plants. Protection of population and environment against radioactive and ionizing radiations is anchored in corresponding laws, in which, as a rule, strict limits of personal doses are determined.

In spite of the fact that radioactivity is insensible by human senses, we are able to discover - detect and measure it quite easily and very precisely. Radioactive substances have one very important property - their activity decreases with time. The time necessary for change of half of nuclei present at the beginning is called the half time. Nuclear change is a statistical event and its probability is equal for all time intervals.

Radioactivity is denoted in units Bq (becquerel) while 1 Bq represents one disintegration per second.  Extent of impacts of radioactive radiation on human organism is given by the amount of absorbed radiation energy in unit of mass of the body. This quantity is called the absorbed dose and it has unit Gy (gray), while 1 Gy = 1 J/kg. Quantitative assessment of influence of different types of radiation on biological material is expressed by so called effective dose, which represents product of absorbed dose and non-dimensional quality factor determined for the given type of radiation. The unit of effective dose is Sv (sievert), having, equally as gray, measure J/kg.