Radioactive source

A radioactive source is a specific quantity of a radionuclide. A radionuclide is a type of atom that emits ionizing radiation. This radiation can take several forms. These include gamma rays, alpha particles, beta particles, and neutron radiation.

These sources are vital for many modern tasks. They can perform irradiation on a target material. This means the radiation performs a significant function on that material. They also serve as metrology sources. These help calibrate instruments used for radiation protection and process monitoring.

Scientists choose specific radionuclides based on their unique properties. They look at the type of radiation emitted. They also consider the intensity of that emission. The half-life of the decay is another key factor. The half-life is the time it takes for the radioactivity to decrease. Common examples include cobalt-60, iridium-192, and strontium-90.

Most irradiation sources last between 5 and 15 years. After this time, their activity drops below useful levels. However, some sources with long half-lives can last much longer when used for calibration.

There are two primary ways to contain these materials. Many sources are "sealed sources." This means the material is permanently contained in a capsule. It might also be firmly bonded to a surface. Capsules are often made of inert metals. These include stainless steel, titanium, or platinum.

Using a sealed container prevents the material from spreading into the environment. However, the container is not meant to stop the radiation. Extra shielding is still required for safety. Unsealed sources are different because they are not in a permanent container. These are often used in medicine. A doctor might dissolve an unsealed source in a liquid for an injection or ingestion.

To manage safety, the IAEA categorizes sealed sources. They use a ratio called A/D to group them. The "A" represents the actual activity of the source. The "D" represents the minimum dangerous activity. A dangerous source is one that could cause significant injury to humans. Category 1 sources have an A/D ratio of 1 or greater. Category 2 sources range from 10 to 1,000. Category 3 sources range from 1 to 10. Category 4 sources range from 0.01 to 15. Category 5 sources have a ratio of less than 0.01.

Sources with very low output, like those in smoke detectors, are not categorized because they do not harm humans.

Measuring these sources requires specific scientific units. The SI unit for source activity is the Becquerel. Some places, like the United States, still use the historical unit called the Curie. However, the NIST advises using the SI unit. In the European Union, using the SI unit for health purposes is mandatory.

Sources are also used for calibration of instruments. Capsule sources act as a single point of radiation. These are used to calibrate beta, gamma, and X-ray instruments. Plate sources have material fixed to a surface. These are used to calibrate large area detectors for contamination surveys.

Radioactive sources have many practical uses in our world. In medicine, they are used for radiation therapy. In industry, they are used for industrial radiography and sterilization. They can also be used for food irradiation and vermin disinfestation. Some industries use them for thickness gauging in paper and steel production. They can even be used for the irradiation crosslinking of PVC.

These diverse applications show how important controlled radiation is to technology.

Proper disposal is a major challenge for the nuclear industry. Expired sources must be handled carefully. Some low-level sources are inactive enough for normal landfill disposal. Higher-level waste requires more complex methods. This might involve using boreholes at various depths. We must be careful to avoid accidents. For example, the Goiânia accident involved a high-level source and caused several deaths. In 1994, there was also a theft of caesium-137 material in Tammiku, Estonia. These events remind us why strict control and safety are necessary.