Caesium-137
Caesium-137, cesium-137, or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission ofuranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. Caesium has a relatively low boiling point of and easily becomes volatile when released suddenly at high temperature, as in the case of the nuclear accident and with nuclear explosions, and can travel very long distances in the air. After being deposited onto the soil as radioactive fallout, it moves and spreads easily in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. Caesium-137 was discovered by Glenn T. Seaborg and Margaret Melhase.
Decay
Caesium-137 has a half-life of about 30.04years, decaying by beta emission to stable barium-137. About94.6% of the decays go to a metastable nuclear isomer of barium: barium-137m and the remainder directly to the ground state. Barium-137m has a half-life of about 153seconds, its dropping to the ground state usually emitting photons having energy. This is responsible for all of the gamma ray emissions in samples of.Uses
Caesium-137 has a number of practical uses. In small amounts, it is used to calibrate radiation-detection equipment. In medicine, it is used in radiation therapy. In industry, it is used in flow meters, thickness gauges, moisture-density gauges, and in borehole logging devices.Caesium-137 is not widely used for industrial radiography because it is hard to obtain a very high specific activity material with a well defined shape, as caesium from used nuclear fuel contains stable caesium-133 and also long-lived caesium-135. Isotope separation is too costly compared to cheaper alternatives. Also, the higher specific activity caesium sources tend to be made from highly soluble caesium chloride; as a result, if a radiography source were to be damaged, the risk of radioactive contamination is high. It is possible to make water-insoluble caesium sources but their specific activity will be lower. Other chemically inert caesium compounds include caesium-aluminosilicate-glasses akin to the natural mineral pollucite. The latter has been used in demonstrations of chemically stable water-insoluble forms of nuclear waste for disposal in deep geological repositories. A large emitting volume will harm the image quality in radiography. The isotopes and are preferred for radiography, since iridium and cobalt are chemically non-reactive metals and can be obtained with much higher specific activities by the activation of stable and in high-flux reactors. However, while is a waste product produced in great quantities in nuclear fission reactors, and are specifically produced in commercial and research reactors and their life cycle entails the destruction of the involved high-value elements. Cobalt-60 decays to stable nickel, whereas iridium-192 can decay to either stable osmium or platinum. Due to the residual radioactivity and legal hurdles, the resulting material is not commonly recovered even from "spent" radioactive sources, meaning in essence that the entire mass is "lost" for non-radioactive uses.
As an almost purely synthetic isotope not existing in the environment before1945, caesium-137 has been used to date wine and detect counterfeits and as a relative-dating material for assessing the age of sedimentation occurring after1945.
Caesium-137 is also used as a radioactive tracer in geologic research to measure soil erosion and deposition; its affinity for fine sediments is useful in this application.
Health risks
The biological behaviour of caesium is similar to that of potassium and rubidium. After entering the body, caesium gets more or less uniformly distributed throughout the body, with the highest concentrations in soft tissue. However, unlike group2 radionuclides like radium and strontium-90, caesium does not bioaccumulate and is excreted relatively quickly. The biological half-life of caesium is about 70days. It has been demonstrated that pancreatic tissue is a strong accumulator and secretor in the intestine of radioactive caesium.A 1961 experiment showed that mice dosed with of had a 50% fatality rate within 30days, implying an LD50 of. A similar experiment in1972 showed that when dogs are subjected to a whole body burden of of caesium-137, they die within 33days, while animals with half of that burden all survived for ayear. A1960 mouse study found there were high levels of for the first day after exposure in the mucus glands of the colon, the pancreas, cartilage, tendons, and skeletal muscle. After 24 hours, cartilage and skeletal muscle showed the highest activity.
In2003, a study found that children from the -polluted area in Belarus near suffered from chronic diseases rarely found in children in other areas of Belarus. Measurements of exposure from autopsies performed on 52 children who died of various causes found that the concentration of was highest in the thyroid, adrenals, and pancreas, and lowest in the brain and liver.
Accidental ingestion of caesium-137 can be treated with Prussian blue, which binds to it chemically and reduces its biological half-life to 30days.
Environmental contamination
Caesium-137, along with other radioactive isotopes caesium-134, iodine-131, xenon-133, and strontium-90, were released into the environment during nearly all atmospheric nuclear weapon tests, and more recently some nuclear accidents, most notably the disaster, the Goiânia Accident and the disaster.Caesium-137 is produced from the nuclear fission of plutonium and uranium, and by observing the characteristic gamma rays emitted by this isotope, one can determine whether the contents of a given sealed container were made before or after the first atomic bomb explosion, which spread some of it into the atmosphere, quickly distributing trace amounts of it around the globe. This procedure has been used by researchers to check the authenticity of certain rare wines, most notably the purported "Jefferson bottles". Surface soils and sediments are also dated by measuring the activity of.
Nuclear bomb fallout
Bombs in the Arctic area of and bombs detonated in or near the stratosphere released caesium-137 that landed in upper Lapland, Finland. Measurements of caesium-137 in the region in the1960s were reportedly 45,000becquerels. Figures from2011 have a midrange of about 1,100becquerels, but no increase in cancer cases has been identified.Chernobyl disaster
As of today and for the next few hundred years or so, caesium-137 and strontium-90 continue to be the principal source of radiation in the zone of alienation around the nuclear power plant, and pose the greatest risk to health, owing to their approximately 30-yearhalf-life and biological uptake. The mean contamination of caesium-137 in Germany following the Chernobyl disaster in 1986 was. This corresponds to a contamination of of caesium-137, totaling about 500grams deposited over all of Germany. In Scandinavia, some reindeer and sheep exceeded the Norwegian legal limit 26years after. The caesium-137 has now decayed by more than half, but could have been locally concentrated by much larger factors.Fukushima Daiichi disaster
In April 2011, elevated levels of caesium-137 were also being found in the environment after the nuclear disasters in Japan. In July2011, meat from 11cows shipped to from Prefecture was found to have perkilogram of, considerably exceeding the Japanese legal limit of 500becquerels perkilogram at that time. In March2013, a fish caught near the plant had a record 740,000becquerels perkilogram of radioactive caesium, above the 100becquerels per kilogram government limit. A 2013 paper in Scientific Reports found that for a forest site from the stricken plant, concentrations were high in leaf litter, fungi and detritivores, but low in herbivores. By the end of2014, "Fukushima-derived radiocaesium had spread into the whole western North Pacific Ocean", transported by the North Pacific current from Japan to the Gulf of Alaska. It has been measured in the ocean surface layer down to and south of the current area down to.Caesium-137 is reported to be the major health concern in. A number of techniques are being considered that will be able to strip out of the caesium from contaminated soil and other materials efficiently and without destroying the organic material in the soil. These include hydrothermal blasting. The caesium, precipitated with ferric ferrocyanide would be the only waste requiring special burial sites. The aim is to get annual exposure from the contaminated environment down to above background levels. The most contaminated area where radiation doses are greater than must remain off-limits, but some areas that are currently less than may be decontaminated, allowing 22,000residents to return.