Ionizing radiation

What is Ionizing Radiation?

Dose and Source


  • Only the amount of energy of any type of ionizing radiation that imparted to (or absorbed by) the human body can cause harm to health.
  • To look at biological effects, we must know (estimate) how much energy is deposited per unit mass of the part (or whole) of our body with which the radiation is interacting.
  • The international (SI) unit of measure for absorbed dose is the gray (Gy), which is defined as 1 joule of energy deposited in 1 kilogram of mass. The old unit of measure for this is the rad, which stands for "radiation absorbed dose." - 1 Gy = 100 rad.
  • Equivalent dose – the biological effect depends not only on the amount of the absorbed dose but also on the intensity of ionisation in living cells caused by different type of radiations.
  • Neutron, proton and alpha radiation can cause 5-20 times more harm then the same amount of the absorbed dose of beta or gamma radiation.
  • The unit of equivalent dose is the sievert (Sv). The old unit of measure is the rem. - 1 Sv = 100 rem.

Sources of Radiation Exposure

  • Radiation is permanently present throughout the environment, in the air, water, food, soil and in all living organisms.
  • Large proportion of the average annual radiation dose received by people results from natural environmental sources.
  • Each member of the world population is exposed, on average, to 2.4 mSv/yr of ionizing radiation from natural sources.
  • In some areas (in different countries of the world) the natural radiation dose may be 5 to 10-times higher to large number of people.