Some things are very tiny. 
Some tiny things are made in big power plants. One is called caesium-137.
It can help doctors treat sick people. It also helps machines check how thick things are.
But this tiny thing can also be dangerous. It can travel far in the air. It can even move through the soil with water.
If it gets into the ground, it stays there for a long time. It can move into plants and animals.
Scientists use it to learn about the past. They even use it to check old wine! 
Caesium-137 is a radioactive material. It is made in nuclear reactors. It is also made by nuclear weapons. Glenn T. Seaborg and Margaret Melhase discovered it.
This material has a half-life of about 30.04 years. A half-life is the time it takes for half of the material to decay. When it decays, it turns into barium. This change gives off gamma rays. These are a type of energy.
Caesium-137 has many uses. Doctors use it in radiation therapy to treat sick people. 
But it can be dangerous. It can travel far in the air. It can also move through soil in water.
Caesium-137 is a special kind of radioactive material. It is an isotope, which means it is a specific version of the element caesium. This material is made during nuclear fission. Fission is the process where the center of an atom splits apart. This happens inside nuclear reactors and nuclear weapons. It also happens through something called spontaneous fission in uranium-238. Because it is made this way, it is a common product of nuclear energy.
This material works through a process called decay. It has a half-life of about 30.04 years. A half-life is the time it takes for half of the material to disappear. When it decays, it turns into a different element called barium. Most of the time, it turns into a version called barium-137m. This version is unstable and drops to a lower state after about 153 seconds. During this change, it releases gamma rays. These rays are a powerful form of energy.
Scientists Glenn T. Seaborg and Margaret Melhase discovered this isotope. Since the first atomic bomb test in 1945, it has been in our atmosphere. This is because nuclear tests released it into the air. Because it did not exist in nature before 1945, we can use it as a tool. Researchers use it to date things like old wine. They also use it to study how soil moves and settles over time. It acts like a tiny marker in the ground.
Caesium-137 has many helpful uses in our world. In medicine, doctors use it for radiation therapy to help treat patients. 

We must be careful because this material can be dangerous. It can travel long distances in the air if it gets hot. It also moves easily through soil because it dissolves in water. Major accidents like Chernobyl and Fukushima released it into the environment.
Caesium-137 is a radioactive isotope of the element caesium. An isotope is a specific version of an element with a unique atomic structure. This particular isotope is a common fission product. It is created during nuclear fission, which is the splitting of atoms like uranium-235. This process happens inside nuclear reactors and nuclear weapons. Trace amounts also come from the spontaneous fission of uranium-238. Because it is a byproduct of nuclear energy, it is a major concern for environmental safety.
The behavior of caesium-137 is defined by its radioactive decay. It has a half-life of approximately 30.04 years. A half-life is the time required for half of the radioactive atoms to decay. During this process, the isotope undergoes beta emission. This means it releases a particle to become a stable form of barium, known as barium-137. About 94.6% of these decays result in a metastable nuclear isomer called barium-137m. This isomer is unstable and lasts for about 153 seconds. When it finally drops to its ground state, it emits photons. These photons are responsible for the gamma ray emissions seen in caesium-137 samples.
Scientists Glenn T. Seaborg and Margaret Melhase discovered this isotope. Since the first atomic bomb test in 1945, caesium-137 has been present in the Earth's atmosphere. Because it is an almost purely synthetic isotope, it did not exist in nature before 1945. This unique history allows researchers to use it for dating. For example, it can be used to check the authenticity of rare wines. It is also used as a relative-dating material. Scientists measure it to assess the age of soil sedimentation occurring after 1945.
Caesium-137 has several practical applications in science and industry. In medicine, it is used for radiation therapy to treat patients. 
Environmental contamination can occur through nuclear accidents or testing. Atmospheric nuclear tests released caesium-137 into the air. This material can travel very long distances because it becomes volatile at high temperatures. Once it lands on soil, it moves easily because its common chemical salts are highly water-soluble. The 1986 Chernobyl disaster caused widespread contamination. In Germany, the contamination covered an area roughly the size of the state of North Rhine-Westphalia. In Scandinavia, some reindeer and sheep exceeded legal radiation limits 26 years after the accident.
The Fukushima Daiichi disaster in 2011 also released significant amounts of the isotope. By 2014, the radiocaesium had spread throughout the western North Pacific Ocean. It was detected in the ocean surface layer as far south as 35°N and as far west as 155°E. In the food chain, concentrations were found to be high in fungi and leaf litter. In July 2011, meat from cows in Fukushima Prefecture exceeded the Japanese legal limit.
Accidental exposure has occurred in several historical incidents. In 1987, the Goiânia accident in Brazil involved the sale of glowing caesium salt from an abandoned clinic. This led to four deaths and several injuries. In 1989, a capsule was found inside a concrete wall in Kramatorsk, Ukraine. By the time it was discovered, six residents had died. In 1994, a theft in Estonia resulted in a fatal dose for one person. These incidents highlight the danger of improperly managed radioactive sources. Managing these materials requires strict safety protocols to prevent human and environmental harm.
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