Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

## Prevention

The best prevention for radiation sickness is to minimize the dose suffered by the human, or to reduce the dose rate.

### Time

The longer that the humans are subjected to radiation the larger the dose will be. The advice in the nuclear war manual entitled "Nuclear War Survival Skills" published by Cresson Kearny in the U.S. was that if one needed to leave the shelter then this should be done as rapidly as possible to minimize exposure.

In chapter 12 he states that "Quickly putting or dumping wastes outside is not hazardous once fallout is no longer being deposited. For example, assume the shelter is in an area of heavy fallout and the dose rate outside is 400 R/hr enough to give a potentially fatal dose in about an hour to a person exposed in the open. If a person needs to be exposed for only 10 seconds to dump a bucket, in this 1/360th of an hour he will receive a dose of only about 1 R. Under war conditions, an additional 1-R dose is of little concern."

In peacetime radiation workers are taught to work as quickly as possible when performing a task which exposes them to irradiation. For instance, the recovery of a lost radiography source should be done as quickly as possible.

$Dose$

### Distance

The radiation due to any point source will obey the inverse square law: by doubling the distance the dose rate is quartered. This is why radiation workers are always taught to pick up a gamma source with a pair of tongs rather than their hand.

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

### Shielding

By placing a layer of a material which will absorb the radiation between the source and the human, the dose and dose rate can be reduced. For instance, in the event of a nuclear war, it would be a good idea to shelter within a building with thick stone walls (Fallout shelter). During the height of the cold war, fallout shelters were identified in many urban areas. It is interesting to note that, under some conditions, shielding can increase the dose rate. For instance, if the electrons from a high energy beta source (such as 32P) strike a lead surface, X-ray photons will be generated (radiation produced in this way is known as bremsstrahlung). It is best for this reason to cover any high Z materials (such as lead or tungsten) with a low Z material such as aluminium, wood, plastic. This effect can be significant if a person wearing lead-containing gloves picks up a strong beta source. Also, gamma photons can induce the emission of electrons from very dense materials by the photoelectric effect; again, by covering the high Z material with a low Z material, this potential additional source of exposure to humans can be avoided. Furthermore, gamma rays can scatter off a dense object; this enables gamma rays to "go around corners" to a small degree. Hence, to obtain a very high protection factor, the path in/out of the shielded enclosure should have several right angle (90 degree) turns rather than just one.

### Reduction of incorporation into the human body

Potassium iodide (KI), administered orally immediately after exposure, may be used to protect the thyroid from ingested radioactive iodine in the event of an accident or terrorist attack at a nuclear power plant, or the detonation of a nuclear explosive. KI would not be effective against a dirty bomb unless the bomb happened to contain radioactive iodine, and even then it would only help to prevent thyroid cancer.

### Fractionation of dose

While Devair Alves Ferreira received a large dose during the Goiânia accident of 7.0 Gy, he lived while his wife received a dose of 5.7 Gy and died. 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, giving her body less time to repair some of the damage done by the radiation. In the same way, some of the people who worked in the basement of the wrecked Chernobyl 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) causes death.