Radiation poisoning, also called "radiation sickness", is a form of damage to organic tissue due to excessive exposure to ionizing radiation. The term is generally used to refer to acute problems caused by a large dosage of radiation in a short period. Many of the symptoms of radiation poisoning occur as ionizing radiation interferes with cell division. This interference causes particular problems for otherwise normally rapidly dividing cells, such as those lining the gastrointestinal tract.
The rad is a unit of absorbed radiation dose in terms of the energy actually deposited in the tissue. The rad is defined as an absorbed dose of 0.01 joules of energy per kilogram of tissue. The more recent SI unit is the gray, which is defined as 1 joule of deposited energy per kilogram of tissue. To assess the risk of radiation, the absorbed dose is multiplied by the relative biological effectiveness of the radiation to get the biological dose equivalent in rems or sieverts (Sv). The sievert is equal to 100 rems.
The biologically effective dose in rems is the radiation dose in rads multiplied by a "quality factor", which is an assessment of the effectiveness of that particular type and energy of radiation. For alpha particles the relative biological effectiveness (RBE) may be as high as 20, so that one rad is equivalent to 20 rems, same goes for neutron radiation. However, for beta particles, x-rays and gamma rays, the RBE is taken as one so that the rad and rem are equivalent for those radiation sources.
Symptoms and Effects
The symptoms of radiation sickness become more serious (and the chance of survival decreases) as the dosage of radiation increases. Prolonged exposure to radiation can cause cancer. Ironically, the ability of radiation to disturb cell division is also used to treat cancer (see radiotherapy), and low levels of ionizing radiation have been shown to lower one's risk of cancer (see hormesis).
Radiation poisoning can result from accidental exposure to natural or industrial radiation sources. People working with radioactive materials often wear film "badges" or other dosimeters to monitor their total exposure to radiation. These devices are more apropos than Geiger counters for determining biological effects, as they measure cumulative exposure over time, and are calibrated to change color or otherwise signal the user before exposure reaches unsafe levels.
Radiation caused illness and death after the bombings of Hiroshima and Nagasaki in about 1% of those exposed who survived the initial explosions. The casualty rate due to radiation was higher in Hiroshima, because although Fat Man (the bomb used at Nagasaki) had a higher yield than Little Boy (the bomb used at Hiroshima), Fat Man was a plutonium weapon, which is much less radioactive than a uranium weapon of equal yield (except at the moment of critical mass). Both bombs were airbursted, minimizing nuclear fallout (which would have killed many more).
Radiation poisoning also continues to be a major concern after the Chernobyl reactor accident. Of the 100 million curies (4 exabecquerels) of radioactive material, the radioactive xenon-133 and iodine-131 Chernobyl released were initially the most dangerous. Due to their short half-lives they have now (2004) decayed, leaving the more long-lived cesium-137 and strontium-90 as main dangers. Thirty-one people died as an immediate result of the Chernobyl accident.
Table of exposure levels and symptoms
Dose-equivalents are presently stated in sieverts:
0.05 - 0.2 Sv
No symptoms. Potential cancer and mutation of genetic material, according to the LNT model. This is disputed. (Note: see hormesis)
0.2 - 0.5 Sv
No noticeable symptoms. Number of erythrocytes decreases temporarily.
0.5 - 1 Sv
Mild radiation sickness with headache and increased risk of infection. Temporary male sterility is possible.
1 - 2 Sv
Light radiation poisoning, 10% fatality after 30 days (LD 10/30). Typical symptoms include mild to moderate nausea (50% probability at 200 rad), with occasional vomiting, beginning 3 to 6 hours after irradiation and lasting for up to one day. This is followed by a 10 to 14 day anastasis, after which light symptoms like general illness, anorexia and fatigue (50% probability at 200 rad). The immune system is depressed, with convalescence extended and increased risk of infection. Temporary male sterility is common.
2 - 3 Sv
Severe radiation poisoning, 35% fatality after 30 days (LD 35/30). Nausea is common (100% at 300 rad), with 50% risk of vomiting at 280 rad. Symptoms onset at 1 to 6 hours after irradiation and last for 1 to 2 days. After that, there is a 7 to 14 day anastasis, after which the following symptoms appear: loss of hair all over the body (50% probability at 300 rad), fatigue and general illness. There is a massive loss of leukocytes, greatly increasing the risk of infection. Permanent female sterility is possible. Convalescence takes one to several months.
3 - 4 Sv
Severe radiation poisoning, 50% fatality after 30 days (LD 50/30). As with 200 to 300 rad dosage, with uncontrollable bleeding in the mouth, under the skin and in the kidneys (50% probability at 400 rad) in the post-anastatic period.
4 - 6 Sv
Acute radiation poisoning, 60% fatality after 30 days (LD 60/30). Fatality increases from 60% at 450 rad to 90% at 600 rad (unless there is intense medical care). Symptoms start half an hour to two hours after irradiation and last for up to 2 days. After that, there is a 7 to 14 day anastasis, after which generally the same symptoms appear as with 300 to 400 rad irradiation, with increased intensity. Female sterility is common at this point. Convalescence takes several months to a year. The primary causes of death (in general 2 to 12 weeks after irradiation) are infections and internal bleeding.
6 - 10 Sv
Acute radiation poisoning, 100% fatality after 14 days (LD 100/14). Survival depends on intense medical care. Bone marrow is nearly or completely destroyed, so a bone marrow transplantation is required. Gastric and intestinal tissue are severely damaged. Symptoms start 15 to 30 minutes after irradiation and last for up to 2 days. Subsequently, there is a 5 to 10 day anastasis, after which the person dies of an infection or internal bleeding. Recovery would take several years and probably never be complete.
10 - 50 Sv
Acute radiation poisoning, 100% fatality after 7 days (LD 100/7). A dose this high leads to spontaneous symptoms after 5 to 30 minutes. After powerful fatigue and immediate nausea caused by direct activation of chemical receptors in the brain by the irradiation, there is a period of several days of comparable well-being, called the "walking ghost phase". After that, cell death in the gastric and intestinal tissue, causing massive diarrhea, intestinal bleeding and loss of water, leads to water-electrolyte imbalance. Death sets in with delirium and coma due to breakdown of circulation. Death is inevitable; the only treatment that can be offered is pain therapy.
50 - 80 Sv
Immediate disorientation and coma in seconds or minutes. Death sets in after a few hours by total collapse of nervous system.
U.S. military forces expect immediate death. A worker receiving 100 Sv in an accident at Wood River, Rhode Island, USA on 24 July 1964 survived for 49 hours after exposure.