The term “Radiological Emergency” generally refers to events involving the release of significant levels of radioactivity and the exposure of workers or the general public to radiation as a result of a Nuclear or Radiological Accident. The source of the hazard is ionising radiation – the flux of alpha, beta or gamma particles which is basically the result of radioactive decay. When the energy of radiation is absorbed by matter, chemical changes occur at the atomic and molecular levels. The amount of radiation energy absorbed per gram of matter is called the absorbed dose. The damage to the tissue from a high dose of radiation is so extensive that the body does not have time to regenerate new tissue, and so the effect becomes visible with many of the features of thermal burning, but it is usually much deeper and longer lasting. Extremely high levels of acute radiation exposure can result in death within a few hours, days or weeks.
Humans are primarily exposed to natural radiation from the sun, cosmic rays and naturally occurring radioactive elements found in rocks, food and the environment. Radon, which emanates from the ground, is another major source of natural radiation. Cosmic rays from space include energetic protons, electrons, gamma rays and x-rays.
The primary radioactive elements found in the Earth’s crust are uranium, thorium and potassium, and their radioactive derivatives. These elements emit alpha and beta particles, or gamma rays.
The average doses of population exposure due to all nuclear industry and man-made radioactive sources amount to about 1% of doses due to natural radiation, but exposure in the event of a nuclear or radiological accident can be far higher and enough to cause death.