First, the cell may no longer perform its function due to internal ionization; this requires a dose to the cell of about gray 10, rad. This requires a dose of 2 gray rad , which will cause reproductive death in half the cells irradiated hence such a quantity is called a "mean lethal dose. Death may also result if cell reproduction ceases in parts of the body where cells are continuously being replaced at a high rate such as the blood cell-forming tissues and the lining of the intestinal tract.
A very high dose of gray 10, rad to the entire body causes death within twenty-four to forty-eight hours; a whole-body dose of 2. These effects were once called nonstochastic; they are now called deterministic. What long-term effects can radiation have? The effect of the radiation may not be to kill the cell, but to alter its DNA code in a way that leaves the cell alive but with an error in the DNA blueprint. The effect of this mutation will depend on the nature of the error and when it is read.
Since this is a random process, such effects are now called stochastic. How can ionizing radiation cause cancer? Cancer is produced if radiation does not kill the cell but creates an error in the DNA blueprint that contributes to eventual loss of control of cell division, and the cell begins dividing uncontrollably. This effect might not appear for many years. Cancers induced by radiation do not differ from cancers due to other causes, so there is no simple way to measure the rate of cancer due to radiation.
During the period studied by the Advisory Committee, great effort was devoted to studies of irradiated animals and exposed groups of people to develop better estimates of the risk of cancer due to radiation. This type of research is complicated by the variety of cancers, which vary in radiosensitivity. For example, bone marrow is more sensitive than skin cells to radiation-induced cancer. Because the cancers can occur anytime in the exposed person's lifetime, these studies can take seventy years or more to complete.
For example, the largest and scientifically most valuable epidemiologic study of radiation effects has been the ongoing study of the Japanese atomic bomb survivors. Other important studies include studies of large groups exposed to radiation as a consequence of their occupation such as uranium miners or as a consequence of medical treatment.
Radiation may alter the DNA within any cell. Cell damage and death that result from mutations in somatic cells occur only in the organism in which the mutation occurred and are therefore termed somatic or nonheritable effects.
For beta, gamma and X-ray radiation, this number is generally one. For some neutrons, protons, or alpha particles, the number is twenty. Since brain cells do not reproduce, they won't be damaged directly unless the exposure is 5, rems or greater. Like the heart, radiation kills nerve cells and small blood vessels, and can cause seizures and immediate death.
Certain body parts are more affected by exposure to different types of radiation sources than others. The thyroid gland is susceptible to radioactive iodine. In sufficient amounts, radioactive iodine can destroy all or part of the thyroid. Taking potassium iodide can reduce the effects of exposure.
When a person is exposed to around rems, the blood's lymphocyte cell count will be reduced, leaving the victim more susceptible to infection. This is often referred to as mild radiation sickness. Our bodies are full of water, and almost all cells have DNA, but some cells and tissues are more susceptible to damage from nuclear radiation than others.
The cells and organs that are most affected by nuclear radiation are the ones that are actively reproducing, because the DNA is more exposed when the cell is in the process of dividing.
Blood cells have the highest turnover rate in our bodies, so the tissue where they are produced — the rapidly dividing cells of the bone marrow — is the most susceptible to radiation damage. The damage to bone marrow in high doses — and complete destruction of it in very high doses — impairs our immune system by not replacing our white blood cells. Long-term exposure to lower doses can lead to cancerous DNA mutations in the marrow, which can lead to the blood cancer leukaemia in people exposed through work or location.
The cells lining the digestive system are also fast-dividing, so they can cope with the physical and chemical assault of digesting our food. Gastrointestinal damage contributes to the symptoms of acute radiation syndrome in people who are exposed to high doses.
Developing foetuses are, of course, incredibly susceptible to radiation, while slow-dividing tissues like muscle and nerve cells are far less sensitive. And healthy tissues and organs are not the only cells that regularly reproduce — tumours are literally balls of cells that are dividing out of control, which is why radiation therapy can be effective in destroying them.
The good blood supply feeding tumours helps too, because the radiation interacts with the dissolved oxygen in the blood as well. That leads to the production of free radicals which attack the nearby cells, amplifying the radiation's effect.
Exposure to external radiation is one thing, but ingesting radioactive particles takes the damage to another level. Inhaling or swallowing radioactive material delivers the source of radiation directly to your cells, increasing the risk of cancer developing in the tissues where they accumulate. Radioactive iodine iodine blown into the atmosphere by the Chernobyl explosion caused a large number of cases of thyroid cancer in people who drank contaminated milk.
Having been released in the clouds of radioactive material following the explosion, the iodine — a by-product of nuclear fission reactions — landed on fields where it was swallowed by cows. Iodine is essential for the normal function of the thyroid gland, and with its knack for attracting iodine the gland gets a concentrated dose of iodine when contaminated milk is drunk.
Thankfully, thyroid cancer is treatable by removal of the gland, although a lifetime of hormone supplements follows. At or below these levels, the enzymes that repair DNA keep up with damage enough to keep the risk of cancer low. According to reports, radiation levels have fluctuated at Fukushima, rising at one reading to millisieverts per hour.
At that level, Dedon says, seven minutes would bring you to the U. Over an hour could be a lethal dose. The millisieverts level was not a sustained measurement and levels continue to fluctuate much lower. Dedon stresses that because radiation dissipates, like light, by the square of its distance, even if levels are high in the plant, just a few miles away, they would be miniscule.
The greater danger for people living in the area is the release of radioactive particles into the air, which can accumulate in the body, damaging tissue over time and causing cancer.
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