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Cells are least sensitive when in the S phase, then the G 1 phase, then the G 2 phase, and most sensitive in the M phase of the cell cycle.This is described by the 'law of Bergonié and Tribondeau', formulated in 1906: X-rays are more effective on cells which have a greater reproductive activity.
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.
For an exposure of 1 roentgen by gamma rays with an energy of 1 MeV, the dose in air will be 0.877 rad, the dose in water will be 0.975 rad, the dose in silicon will be 0.877 rad, and the dose in averaged human tissue will be 1 rad. [10] "rad" stands for radiation absorbed dose. [4]
Radiation sensitivity is the susceptibility of a material to physical or chemical changes induced by radiation. [1] Examples of radiation sensitive materials are silver chloride, photoresists and biomaterials. Pine trees are more radiation susceptible than birch due to the complexity of the pine DNA in comparison to the birch.
Radioresistance is the level of ionizing radiation that organisms are able to withstand.. Ionizing-radiation-resistant organisms (IRRO) were defined as organisms for which the dose of acute ionizing radiation (IR) required to achieve 90% reduction (D10) is greater than 1,000 gray (Gy) [1]
The roentgen or röntgen (/ ˈ r ɛ n t ɡ ə n,-dʒ ə n, ˈ r ʌ n t-/; [2] symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air (statcoulomb per kilogram).
Scanning electron micrograph of SARS virions. Severe acute respiratory syndrome (SARS) is the disease caused by SARS-CoV-1. It causes an often severe illness and is marked initially by systemic symptoms of muscle pain, headache, and fever, followed in 2–14 days by the onset of respiratory symptoms, [13] mainly cough, dyspnea, and pneumonia.