Acute radiation syndrome (ARS), colloquially known as radiation sickness, is a rare yet often fatal set of symptoms that accompanies abnormally high exposure to ionizing radiation. ARS typically includes acute symptoms from single, large dose exposures as opposed to chronic symptoms, which develop from small, prolonged radiation exposure.
The SI derived unit Gray (symbol Gy) measures absorbed radiation and is 1 joule of ionizing radiation absorbed by a 1 kilogram mass. Given these units, there are two types of radiation: non-ionizing radiation (i.e. low frequency microwaves, radio waves, and visible light) and ionizing radiation (i.e. high frequency gamma and X-rays, alpha, beta, and gamma particles). Not only do different tissues have different susceptibilities to absorbing ionizing radiation, but the particle size directly correlates to the amount of damage incurred upon bodily cells; alpha particles are much more massive than beta particles. Moreover, the SI unit of equivalent dose, effective dose, and operational dose quantities is the sievert (Sv) with units joule per kilogram (J kg-1). Equivalent dose is calculated by multiplying the absorbed dose (in Gy) by the weighting factor. Thus, 1 Gy of alpha radiation constitutes a larger equivalent dose (i.e. more sieverts) than 1 Gy of beta particles because alpha particles have a weighting factor of 20 compared to a weighting factor of 1 for beta particles. 
In addition to the well-publicized instances of radiation warfare or radiation accidents at various nuclear power plants, other causes of ARS might be accidental exposure to an industry facility with high emissions of radiation or else excessively and improperly administered medical radiation treatments.  The X-rays that are used in standard medical procedures administer ionizing radiation doses well below 0.1 Gy, while up to 80 Gy might be administered in smaller 1.8-2.0 Gy fractions for combating cancer, such as the relatively radioresistent prostate cancer cells, with radiation therapy. 
Unlike radiation-spawned diseases - like cancer - that manifest over long periods ominously, the symptoms that characterize ARS may appear moments after exposure. Depending on the degree of exposure and on what parts of the body, the telltale symptoms of ARS may occur as soon as few moments after exposure; with a few exceptions, the more severe the exposure in terms of proximity to source and duration of exposure, the greater the severity and the quicker the onset.  Doses as small as 1 Gy can be the start of ARS. Due to differences in ionizing radiation and the varying susceptibility of the body, there are three classic categories of syndromes: hematopoietic, gastrointestinal, and neurovascular. According to the Southern Medical Journal, Hemapoietic Syndrome includes damage to bone marrow and blood cells at excess of 2 Gy; symptoms include anemia, bleeding due to platelet loss, and decreased immunity. Gastrointestinal Syndrome occurs at about 8 Gy of exposure; symptoms include nausea, abdominal cramping, and diarrhea.  Neurovascular Syndrome is the rarest because the nervous system is the least sensitive to ionizing radiation; symptoms include meningitis and damage to cerebral vessels. 
ARS treatment includes bone marrow transplants and granulocyte colony-stimulating factor in addition to protein supplements (i.e. filgrastim) that attempt to stem the dramatic decrease in blood cells. Other chemical supplement treatments attempt to neutralize radioactive particles in the body by binding to the particles and, in so doing, prevent the particles from interacting with the bodily cells.  Unfortunately, death is likely for patients of ARS who have sustained ionizing radiation in excess of 6 Gy. Palliative care is oftentimes the only option remaining.
© Justin Lee. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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