What Is Type S Plutonium?

Plutonium (Pu) is a radioactive, metallic element with the atomic number 94. It was created in 1941 at the University of California, Berkeley, and first produced in large quantities for the second "Fat Man" atomic bomb dropped on Nagasaki, Japan, in World War II. Other uses include its use in nuclear power plant reactors, heart pacemakers and thermoelectric generators for space program instruments.

"Type S" plutonium is one of three classifications (along with Type F and Type M) used by medical researchers and occupational safety experts to describe how quickly the radioactive element is absorbed into the human body.

Plutonium Is a Radioactive Element

• Plutonium is a radioactive element created by bombarding uranium with neutrons (subatomic particles with no net electric charge). The element does not produce strong radiation but can settle in bones or lungs, increasing cancer risk. Although discovered in 1941, it was not revealed to other scientists until 1948 because of national security concerns.

Early Experiments

• Experiments on rodents and dogs in 1944-45 tested how plutonium enters the body (uptake pathways), its distribution in the body, effects on organs and how it is removed from the body. Scientists discovered plutonium oxide, especially fired at high temperatures, is absorbed into the body over years, labeled it Type S (slow). Plutonium nitrate, a soluble chemical form, is absorbed over days and was labeled Type F (fast). Other chemical forms that are absorbed over weeks, such as plutonium fluoride, were labeled Type M. Type S plutonium was found to clear more slowly from the lungs than types M and F. Both Type S and Type M plutonium have a very long half-life (amount of time for half of the element to decay) and are retained in the body for long periods. But the element actually was found to be less acutely toxic to humans than botulism, diphtheria, curare or strychnine.

Three Types of Plutonium

• Type S plutonium, plutonium oxide, is the element's most common form. It is virtually insoluble, although its behavior in the body depends on how it is ingested. If a person eats or drinks it, a large percentage will be eliminated through the body's normal waste disposal system. However if it is inhaled, as much as 20 percent to 60 percent (depending upon particle size and other factors) will be retained in the lungs. The rest is eliminated within several days. The plutonium remaining in the lungs will be eliminated over several years through the body's waste disposal system and traveling to the lymph nodes and other organs (mainly bones and liver).

  If the element enters the body through an open wound it can move directly into organs, depending upon its form. However, this is unlikely due to remote handling by robotic arms and protective clothing. Type M plutonium, such as plutonium fluoride or plutonium chloride, is moderately soluble and clears out of the body more quickly.

  Type F plutonium, plutonium nitrate, is the element's second most common form. It is more soluble than Type S. Its behavior in the body is similar to Type S but it clears out of the lungs more quickly.

Toxicity

• Type S plutonium, along with Types F and M, are toxic if ingested but no more so than many heavy metals, such as iron, cobalt, copper and zinc. Plutonium's principal radiation comes from "alpha particles," which can't penetrate the skin. Inhalation remains the greatest risk. It is not so dangerous that "a speck can kill." Other natural substances are more toxic, such as botulism, and many substances can be toxic if not handled properly.

Common Uses

• Type S plutonium is used in thermoelectric generators used by space probes traveling too far to use solar power, such as the Galileo and Cassini probes to Jupiter. It's also used in navigation beacons, satellites and pacemakers.