By changing molecules in the highly ordered environment of the cell, ionizing radiation can disrupt and damage cells. Ionizing radiation is emitted by radioactive substances (radionuclides), such as uranium, radon, and plutonium. It is also produced by man-made devices, such as x-ray and radiation therapy machines Radio waves, such as from cell phones and AM and FM transmitters, and visible light also are forms of electromagnetic radiation.

In general, ionizing radiation refers to high-energy electromagnetic waves (x-rays and gamma rays) and particles (alpha particles, beta particles, and neutrons) that are capable of stripping electrons from atoms (ionization). By changing molecules in the highly ordered environment of the cell, ionizing radiation can disrupt and damage cells. Cellular damage can cause illness, increase the risk of developing cancer, or both Ionizing radiation is emitted by radioactive substances (radionuclides), such as uranium, radon, and plutonium.

It is also produced by man-made devices, such as x-ray and radiation therapy machines Radio waves, such as from cell phones and AM and FM transmitters, and visible light also are forms of electromagnetic radiation. However, because of their lower energy, these forms of radiation are not ionizing, and thus public exposure levels from these common sources do not damage cells. In this discussion, "radiation" refers exclusively to ionizing radiation

Measurement of Radiation: The amount of radiation is measured in several different units. The roentgen (R) is a measure of the ionizing ability of radiation in air and is commonly used to express the intensity of exposure to radiation. How much radiation people are exposed to and how much is deposited in their body may be very different. The gray (Gy) and sievert (Sv) are measures of the dose of radiation, which is the amount of radiation deposited in matter, and are the units used to measure dose in humans after exposure to radiation.

The Gy and Sv are similar, except the Sv takes into account the effectiveness of different types of radiation to cause damage and the sensitivity of different tissues in the body to radiation. Low levels of exposure are measured in mGy (1 mGy = 1|1000 Gy) and mSv (1 mSv = 1|1000Sv) Contamination vs. Irradiation: The two main types of radiation exposure are contamination and irradiation.

Many of the most significant radiation accidents have exposed people to both Contamination is contact with and retention of radioactive material, usually as a dust or liquid. External contamination is that on skin or clothing, from which some can fall or be rubbed off, contaminating other people and objects. Internal contamination is radioactive material deposited within the body, which it may enter by ingestion, inhalation, or through breaks in the skin.

Once in the body, radioactive material may be transported to various sites, such as the bone marrow, where it continues to emit radiation, increasing the dose, until it is removed or emits all its energy (decays). Internal contamination is more difficult to remove than external contamination Irradiation is exposure to radiation but not to radioactive material, that is, no contamination is involved.

During the next 4 or 5 days (latent stage), people feel well, but the cells lining the digestive tract, which normally act as a protective barrier, die and are shed. After this time, severe diarrhea—often bloody—returns, once more resulting in dehydration. Bacteria from the digestive tract may invade the body, producing severe infections. People who have received this much radiation also develop the hematopoietic syndrome, which results in bleeding and infection and increases their risk of death.

After exposure to 6 Gy or more of radiation, death is common. However, with advanced medical support, about 50% of people may survive. . The cerebrovascular syndrome occurs when the total dose of radiation exceeds 20 to 30 Gy. People rapidly develop confusion, nausea, vomiting, bloody diarrhea, tremors, and shock. The latent phase is brief or absent. Within hours, blood pressure falls, accompanied by seizures and coma.

The cerebrovascular syndrome is always fatal within a few hours to 1 or 2 days Local Radiation Injury: Radiation therapy for cancer is one of the most common causes of local radiation injuries. Other causes produce similar symptoms. Symptoms depend on the amount of radiation and the area of the body treated

High accumulated doses of radiation to the spinal cord can cause catastrophic damage, leading to paralysis, incontinence, and loss of sensation. Extensive radiation to the abdomen (for lymph node, testicular, or ovarian cancer) can lead to chronic ulcers, scarring, and narrowing or perforation of the intestine, causing symptoms such as abdominal pain, vomiting, vomiting blood, and dark, tarry stools.

Other drugs, such as zinc or calcium diethylenetriamine penta-acetate (DTPA—for plutonium, yttrium, californium, and americium), calcium or aluminum phosphate solutions (for radioactive strontium), and Prussian blue (for radioactive cesium, rubidium, and thallium), can be given intravenously to remove a fraction of certain radionuclides after they have entered the body. However, except for potassium iodide , which is very effective, drugs given to reduce internal contamination reduce exposure by only about 25 to 75%

Such drugs are routinely given to people undergoing radiation therapy or chemotherapy. Dehydration is treated with fluids given intravenously

The outcome depends on the radiation dose, dose rate (how quickly the exposure occurs), and the parts of the body that are affected. Other factors include people's state of health and whether they receive medical care. In general, without medical care, half of all people who receive more than 3 Gy of whole-body radiation at once die. Nearly all people who receive more than 6 Gy die. Nearly all those who receive less than 2 Gy fully recover within 1 month, although long-term complications such as cancer may occur.

With medical care, about half of people survive 6 Gy of whole-body radiation. Some people have survived doses of up to 10 Gy Because doctors are unlikely to know the amount of radiation a person has received, they usually predict outcome by the person's symptoms. The cerebrovascular syndrome is fatal within hours to a few days.