Radiation is energy that moves in the form of waves or particles. This energy is emitted both inside the body and externally, through both natural and man-made processes.

Long-term exposure to small amounts of radiation can lead to gene mutations and increase the risk of cancer, while exposure to a large amount over a brief period can lead to radiation sickness. The ways symptoms manifest in cases of radiation exposure are described below.

• Acute radiation exposure, where an individual is exposed to a large amount of radiation all at once, is usually associated with nausea and vomiting. Headache, weakness and fatigue are other symptoms. The greater the dose of radiation exposure, the more severe these symptoms of radiation sickness will be.
• Initial nausea and vomiting symptoms usually manifest within 12 to 24 hours after mild radiation exposure (1 to 2 Sv or 100 to 200 rems). In cases where exposure has been more intense, these initial symptoms may be followed by a symptom-free period before the symptoms associated with higher doses of radiation start to manifest.
• Exposure to 2 Sv/200 rem of radiation or more causes destruction of any rapidly dividing cells in the body. For example, the intestinal tract lining will be damaged, leading to nausea, bloody vomiting and diarrhea.
• Other tissues made up of rapidly dividing cells are also damaged including the blood, hair follicles and reproductive tissue. Among cells that survive the damage, the DNA and RNA are damaged.
• The annual limit on intake (ALI) is the established limit on how much radiation an adult worker can absorb through ingestion or inhalation over a one year period. The ALI is defined as the amount of radionuclide absorbed over a year that would lead to:
  • an effective dose equivalent of 0.05 Sv for a reference human body..
  • .. or a dose equivalent of 0.5 Sv to any organ or tissue, (whichever dose is smaller).