Истории и востоковедения
The effects on human health
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| The effects on human health
There are two main health effects caused by radiation, which act over the short- and long-term and also at shorter and greater distances. Radiation causes health problems by killing cells in the body, and the amount and type of damage done depends on the dose of radiation received and the time over which the dose is spread out. The dose limits for emergency workers in the event of a nuclear accident are 100 mSv if protecting property or 250 mSv in a life-saving operation. Between that upper limit and 1 Sv received within a single day, exposure is likely to cause some symptoms of radiation poisoning, such as nausea and damage to organs including bone marrow and the lymph nodes. Up to 3 Sv these same effects are more serious with a likelihood of acquiring infections due to a reduced number of white blood cells in the body – with treatment, survival is probable but not guaranteed. 97 Larger doses will, in addition to those symptoms above, cause hemorrhaging, sterility and skin to peel off; an untreated dose of more than 3.5 Sv will be fatal, and death is expected even with treatment for doses of more than 6 Sv. The radiation level decreases with the square of the distance from its source, so someone twice as far away from an external source will receive a quarter of the radiation. Receiving a high dose in a shorter time usually causes more acute damage, as greater doses kill more cells, while the body can have had time to repair some damage with more time having elapsed between doses. However, radioactive material that is spread to a wider area can cause longer-term health effects via prolonged exposure, particularly if they enter the food chain or are inhaled or ingested directly. Taking radioactive materials into the body also presents the greatest danger from atoms that undergo alpha-decay, as alpha particles are not very penetrative and are easily absorbed by a few centimeters of air. Radioactive isotopes of iodine, which undergo beta-decay, can build up in the thyroid gland and can cause thyroid cancer. Attempts to prevent this involve distributing pills that include nonradioactive iodine-127 and which flood the thyroid, preventing uptake of radioactive iodine. For one-off doses, such as those from medical scans, the risk of later developing cancer is estimated at around 1 in 20 000 per mSv received. Absorbing an accumulated dose of 1 Sv over a longer period of time is estimated to eventually cause cancer in 5% of people. However, there is disagreement over whether very small doses comparable to the level of background radiation actually contribute to health effects. (Adopted from www.iop.org ) жүктеу/скачать 1,14 Mb. Достарыңызбен бөлісу:
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