Ionizing radiation is given off by the nucleus of an unstable atom in the process of reaching a stable (ground) state. Radiation from radioactive substances ionizes the matter it passes through (splits the molecules) into charged ions of alpha, beta and gamma particles. These particles in concentration can cause the formation of free radicals, DNA strand mutation and a variety of other unhealthy side-effects.
Tritium, a radionuclide emitted as waste from new-generation nuclear power reactors, passes through the human body in 12 days. However, when the radionuclide unites with carbon in the human body, plants, or animals, it becomes organically bound (OBT) and can remain in the human body for 450 to 650 days. One study found traces of tritium in the body 10 years after exposure.
RADIATION EXPOSURES AND HEALTH EFFECTS
In the United States, members of the general public annually receive an average background radiation dose of about 360 millirem (mrem, mR) from a combination of natural and man-made sources. The primary natural source, radon gas, contributes about 200 mrem, to the average annual dose equivalent, and medical x-rays, the primary man-made source, contribute about 40 mrem. (A typical chest x-ray results in a 10 mrem dose.)
The U.S. Nuclear Regulatory Commission(NRC) has established dose limits for workers exposed to radiation as part of their jobs, and these limits have been adopted (where not otherwise required) by the U.S. Department of Energy(DOE). The annual dose limit for radiological workers overall is 5.0 rem (5,000 mrem) whole body, and for declared pregnant workers, 0.5 rem(500 mrem) to the unborn child (embryo/fetus) over the nine-month gestation period. The average annual dose to the general public from nuclear industry activities is limited to 0.1 rem (100 mrem).
The NRC limits reflect the prevailing assumption among government (and industry and many academic) technical authorities that an individual must receive a whole-body dose of about 25,000 mrem (15,000 mrem for a pregnant woman) before there is a significant increase in the risk of serious human health effects, and a dose of about 500,000 mrem (500 rem) before probable death as a result of radiological health effects. On the other hand, government regulations also require that NRC licensees and DOE contractors follow the radiation control concept known as ALARA (As Low As Reasonably Achievable). The ALARA objective is to attain worker and public doses as far below the applicable limits as reasonably achievable given social, technical, economic and policy considerations. The ALARA concept recognizes the uncertainties associated with the risk of low level exposure to ionizing radiation. It should also be remembered that there is considerable technical controversy about the individual health effects of any additional exposures beyond background levels, and mythological debate about the use of collective population-doses to calculate latent cancer fatalities among the general population in probabilistic risk assessments.
Other online geiger counters:
National Radiation Map - USA
Chernobyl disaster photos by Elena Filatova
Jason Buchanan, firstname.lastname@example.org
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