Acute radiation damage

As we discussed in Section 19.2, the energy associated with radioactivity can ionize molecules. When radiation ionizes important molecules in living cells, problems can develop. The ingestion of radioactive materials—especially alpha and beta emitters—is particularly dangerous because the radioactivity once inside the body can do even more damage. The effects of radiation can be divided into three different types acute radiation damage, increased cancer risk, and genetic effects. 

A The Stanford Linear Accelerator (top) is located at Stanford University in California. The Fermi National Accelerator Laboratory complex in Batavia, Illinois (bottom), includes two cyclotrons in a figure-8 configuration. 

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Acute radiation damage results from exposure to large amounts of radiation in a short period of time. The main sources of this kind of exposure are nuclear bombs and exposed nuclear reactor cores. These high levels of radiation kill large numbers of cells. Rapidly dividing cells, such as those in the immune system and the intestinal lining, are most susceptible. Consequently, people exposed to high levels of radiation have weakened immune systans and a lowered abihty to absorb nutrients from food. In milder cases, recovery is possible with time. In more extreme cases, death results, often from infection. 

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What is acute radiation damage to living organisms ... 

The effects of radiation can be gronped into three categories. Acute radiation damage is cansed by a large exposure to radiation for a short period of time. Lower radiation exposnres may result... 

Health effects from exposure to radiation fall into two categories stochastic (based on probability) and acute. Stochastic effects typically take several years to materialize (e.g., cancer appearing 20 years after an exposure) while acute effects such as nausea or reddening of the skin may take only weeks, days, or even hours to materialize. Stochastic and acute effects are described in more detail in the following sections. First, however, a brief discussion describes how radiation damages human tissue and why exposure may produce one or a combination of the described health effects. 

Acute radiation exposure, which can cause radiation sickness, radiation burns, and so forth, is caused by the energy deposited in the body, and so we are looking for effects that will occur within hours, days, or weeks of the exposure. As cancer takes many years or decades to develop, quantifying the long-term effects of DNA damage resulting from an acute exposure is not as important. In the case of acute radiation exposure, then, we measure only the amount of energy deposited in the body, so we use units of Gy or rad. 

Since acute radiation toxicity responses become apparent shortly after exposme, history is an important criterion in determining whether the radiation is related to the cause of a particular complication or adverse effect. As with any attempt to specify a dose-response relationship, the dose is an important component. In contrast, late radiation toxicity in organs such as the kidneys, fiver, or central nervous system (CNS) will not be seen until months or perhaps even years after radiation exposure (Center for Drug Evaluation, 2005). The integrated response is often to the radiation response and attempts to heal any radiation damage that has been caused. 

Depending on the dose, dose rate and route of exposure, radiation can cause Acute Radiation Syndrome (ARS), cutaneous injury and scarring, chorioretinal damage (due to exposure to infrared energy), and increased long term risk for cancer, cataract formation (especially due to neutron irradiation), infertility and fetal abnormalities, such as growth retardation, fetal malformations, increased teratogen-esis and fetal death (2). 

Some skin damage frequently accompanies ARS. However, the cutaneous syndrome can also result from localized acute radiation exposure to the skin, usually from direct handling of radioactive sources or from contamination of the skin or clothes (2,8) (see Figs. 4.1 and 4.2) With localized exposure, even with high doses, the victim frequently survives, because the whole body usually does not receive the localized dose. However, if a patient with localized radiation induced cutaneous injury has also received whole body irradiation from an external source, the cutaneous damage increases the risk for death from the whole body exposure (2). Patients with the hematopoietic syndrome due to whole body irradiation will recover more slowly, if at all, from cutaneous injury due to bleeding, infection and poor wound healing (2). 

Randall K, Coggle JE. 1995. Expression of transforming growth factor-fll in mouse skin during the acute phase of radiation damage. Int J Radiat Biol 68(3) 301-309. 

Clearly, an exploded nuclear device could result in a lot of property damage. People would be killed or injured from the blast and might be contaminated by radioactive material. Many people could have symptoms of acute radiation syndrome. After a nuclear explosion, radioactive fallout would extend over a large region far from the point of impact, potentially increasing people s risk of developing cancer over time. 

As the levelof radiation increases, the survival period decreases. At about 1000 rad (10 Gy), there will be serious damage to the gastrointestinal tract and survival may be a few weeks. At exposures of several thousand rad, the central nervous system will be strongly affected and survival will be measured in terms of hours. Much of the information above is derived from reference 3. An excellent current (1999) summary of the biological effects of radiation, including more on the acute radiation syndrome is found in the Internet reference to this section. 

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