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Gamma rays, at the high-frequency end of the spectrum, have the highest photon energies and the shortest wavelengths—much smaller than an atomic nucleus. Gamma rays, X-rays, and extreme ultraviolet rays are called ionizing radiation because their high photon energy is able to ionize atoms, causing chemical reactions. Longer-wavelength ...
Typical RF energy levels encountered by the general public are well below the level needed to cause significant heating, but certain workplace environments near high power RF sources may exceed safe exposure limits. [7] A measure of the heating effect is the specific absorption rate or SAR, which
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.
The effect of non-ionizing radiation on chemical systems and living tissue is primarily simply heating, through the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are ionizing – individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds .
However, very high energy particles can produce visible effects on both organic and inorganic matter (e.g. water lighting in Cherenkov radiation) or humans (e.g. acute radiation syndrome). [ 4 ] Ionizing radiation is used in a wide variety of fields such as medicine , nuclear power , research, and industrial manufacturing, but is a health ...
Specific energy absorption rate (SAR) averaged over the whole body or over parts of the body, is defined as the rate at which energy is absorbed per unit mass of body tissue and is expressed in watts per kilogram (W/kg). Whole body SAR is a widely accepted measure for relating adverse thermal effects to RF exposure. [9]
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.
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]