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Prevention
The best prevention for radiation sickness is to minimize the dose suffered by the human, or to reduce the dose rate. The primary methods of prevention include reducing the time one is exposed, increasing the distance from the source of radiation, and using protective shielding.

Time
The longer that humans are subjected to radiation the larger the dose will be.


 * $$ Dose \propto t $$

Distance
The farther away a person is from a radiation source, the less the exposure. By doubling the distance, exposure is reduced by a factor of four. By halving the distance, exposure is increased by a factor of four. (See the inverse square law.) The minimum distance required to ensure safety depends on the energy of the radiation, as well as the size or activity of the source. Alpha radiation and Beta radiation lack the energy to travel very far, while Gamma radiation is capable of travelling long distances.


 * $$ Dose \propto \frac{1}{r^2} $$

Shielding
By placing a layer of material which absorbs radiation between the source and a human, the dose and the dose rate can be reduced. Any material will provide some amount of shielding, but the most commonly used materials are steel, concrete, lead and soil. For instance, in the event of a nuclear war it would be a good idea to shelter within a building with thick concrete walls. In fact, during the height of the cold war when concerns of nuclear warfare were widespread, buildings meeting this criterion were identified as fallout shelters in many urban areas.

The specific type of shielding required to absorb radiation depends on its type:
 * Alpha particles can be shielded with thin materials, such as a piece of paper or the outer layers of human skin. However, there is still a risk of exposure from inhaled or injested particles.
 * Beta particles can be shielded by heavy clothing. Some beta particles can penetrate and burn the skin.
 * Gamma rays (emitted from nuclear fallout, and also used to sterilize medical equipment and food) require thick, dense shielding such as lead. The higher the energy of the gamma radiation, the thicker the lead must be.

Reduction of incorporation into the human body
Potassium iodide (KI), administered orally just before or immediately after exposure, may be used to protect the thyroid from radioactive iodine. Protection lasts approximately 24 hours and must be repeated daily as long as there is a risk of exposure. However, KI does not protect other organs or tissues from absorbing radiation, nor does it prevent the absorption of other radioactive substances.

Fractionation of dose
Fractionated doses, or doses spread out over time, can affect radiation poisoning and survivability. During the Goiânia accident (where residents of Goiânia, Brazil accidently opened an abandoned canister of radioactive materials), the effects of radiation poisoning varied greatly according to exposure over time.

Devair Alves Ferreira, a junk yard owner who purchased the radioactive material to make a ring for his wife, was exposed to a short-term large dose of radiation (7.0 Gy) and lived. His wife, however, received a constant dose of 5.7 Gy over a long period of time and died as a result. The most likely explanation is that his dose was fractionated into many smaller doses which were absorbed over a length of time, while his wife stayed in the house more and was subjected to continuous irradiation without a break. This would give her body less time to repair some of the damage done by the radiation. Similarly, some of the people who worked in the basement of the Chernobyl Nuclear Power Plant received doses of 10 Gy, but in small fractions, so the acute effects were avoided.

It has been found in radiation biology experiments that if a group of cells are irradiated, then as the dose increases, the number of cells which survive decreases. It has also been found that if a population of cells is given a dose before being set aside (without being irradiated) for a length of time before being irradiated again, then the radiation causes less cell death. The human body contains many types of cells and the human can be killed by the loss of a single type of cells in a vital organ. For many short term radiation deaths (3 days to 30 days), the loss of cells forming blood cells (bone marrow) and the cells in the digestive system (microvilli which form part of the wall of the intestines are constantly being regenerated in a healthy human) cause death.

In the graph below, dose/survival curves for a hypothetical group of cells have been drawn, with and without a rest time for the cells to recover. Other than the recovery time partway through the irradiation, the cells would have been treated identically.