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Pay attention to the symptoms that develop, their severity, and their timing. It is possible for doctors to predict the level of radiation exposure from the timing and the nature of the symptoms. The severity of symptoms will vary depending on the radiation dose received, and the parts of the body that absorbed the emissions.  The determining factors in the degree of radiation sickness are the type of exposure, the exposed parts of the body, the duration of exposure, the strength of the radiation, and how much your body has absorbed. The cells in your body that are most sensitive to radiation include the lining of your stomach and intestinal tract, and the cells found in your bone marrow that produce new blood cells. The degree of exposure guides the presentation of symptoms. Initial symptoms involving the gastrointestinal tract can appear within ten minutes. If the skin was directly exposed or contaminated, redness, rash, and burning can begin almost immediately. There is no way to predict the exact course of a radiation exposure event that leads to radiation sickness since there are many variables involved. The symptom presentation is, however predictable. The degree of exposure, ranging from mild to very severe, can alter the timing of symptom development. The following symptoms are consistent with radiation sickness.  Nausea and vomiting Headache Fever Dizziness Disorientation Weakness and fatigue Hair loss Bloody vomit and stools Infections and poor wound healing Low blood pressure Four categories and their ranges of exposure are used to diagnose the levels of severity for radiation sickness. The levels are based on a sudden exposure over a short amount of time. The severity is determined by the degree of exposure and the onset of symptoms.  Mild severity is exposure to radiation that resulted in a body absorption of 1 to 2 gray units (Gy). Moderate severity results after exposure that causes the body to absorb 2 to 6 Gy. Severe exposure results in an absorbed level measured at 6 to 9 Gy. Very severe exposure is absorption at 10 Gy or higher. Doctors can gauge the absorbed dose by measuring the time between exposure and the first signs of nausea and vomiting. Nausea and vomiting that begins within ten minutes of exposure is considered very severe exposure. Mild exposure involves the onset of nausea and vomiting within six hours. Radiation exposure is measured in different ways. In the United States, the level of radiation sickness is described as the amount of radiation absorbed by the body.  Different types of radiation are measured using different units, and to further complicate things, the country you are in may use yet a different unit. In the United States, absorbed radiation is measured in units called a gray, abbreviated as Gy, in rads, or in rem. Generally conversions are as follows: 1 Gy is equal to 100 rads, and 1 rad is equal to 1 rem. The rem equivalent for different types of radiation is not always expressed as just described. The information provided here includes basic conversion factors. Two types of exposure are possible; irradiation and contamination. Irradiation involves exposure to the radiation waves, emissions, or particles, while contamination involves direct contact with radioactive dust or liquid.  Acute radiation sickness only occurs with irradiation. It is possible to have come into direct contact and also have experienced irradiation. Radiation contamination results in absorption of radioactive material through the skin and transportation to the bone marrow where it can result in health problems such as cancer. Radiation sickness is possible but unlikely and actual incidents are rare. Radiation exposure caused by an accident at a work site that uses radiation could cause radiation sickness. Potentially, a natural disaster that alters the integrity of a structure that contains powerful radiation, such as a nuclear power plant, is possible.  Natural disasters, like earthquakes or hurricanes, could potentially damage the integrity of a nuclear facility causing a localized release of potentially dangerous radiation; although this type of structural damage is unlikely. An act of war that involves the use of a nuclear weapon could cause widespread exposure leading to radiation sickness. A terrorist attack using dirty bombs could cause radiation sickness to people in the immediate vicinity. Space travel has risks related to radiation exposure. While possible, it is highly unlikely that exposure from equipment used for medical purposes could lead to the development of radiation sickness. Nuclear energy is all around us. Safeguards are in place to protect the public from accidental exposure.

Summary:
Watch for symptom progression. Identify the symptoms. Consider the level of exposure. Know what the numbers mean. Recognize the method of exposure. Consider possible causes.