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UV is the lowest energy range energetic enough to ionize atoms, separating electrons from them, and thus causing chemical reactions. UV, X-rays, and gamma rays are thus collectively called ionizing radiation; exposure to them can damage living tissue.
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning.Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1,000 of a rem and 1 rem equals 0.01 Sv.
The FCC limits for maximum permissible workplace exposure to shortwave radio frequency energy in the range of 3–30 MHz has a plane-wave equivalent power density of (900/ f 2) mW/cm 2 where f is the frequency in MHz, and 100 mW/cm 2 from 0.3 to 3.0 MHz.
The global average exposure of humans to ionizing radiation is about 3 mSv (0.3 rem) per year, 80% of which comes from nature. The remaining 20% results from exposure to human-made radiation sources, mainly medical imaging. Average human-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine.
Adjustments for photon energy or dose-rate and fractionation have not been made. These types of analysis lend confidence to risk assessments as well as showing the limitations of such data sets. Of special interest to NASA is the dependence on age at exposure of low-LET cancer risk projections.
Surviving the highest known radiation dose in any human Albert Stevens (1887–1966), also known as patient CAL-1 and most radioactive human ever , was a house painter from Ohio who was subjected to an involuntary human radiation experiment and survived the highest known accumulated radiation dose in any human. [ 1 ]
In the 1930s the roentgen was the most commonly used unit of radiation exposure. This unit is obsolete and no longer clearly defined. This unit is obsolete and no longer clearly defined. One roentgen deposits 0.877 rad in dry air, 0.96 rad in soft tissue, [ 9 ] or anywhere from 1 to more than 4 rad in bone depending on the beam energy. [ 10 ]
It is difficult to establish risks associated with low dose radiation. [7] One reason why is that a long period of time occurs from exposure to radiation and the appearance of cancer. [7] Also, there is a natural incidence of cancer. [7] It is difficult to determine whether increases in cancer in a population are caused by low dose radiation. [7]