Plutonium and Plutonium-238

Plutonium is known as the second transuranic element in the actinide series. It was discovered in 1940 by Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan, and Arthur C. Wohl at the University of California, Berkeley. This discovery resulted from the bombardment of uranium-238 isotope with deuterium bombardment.

This process produced neptunium-238 and two free neutron; neptunium-238 then underwent beta decay to become plutonium-238. The discovery of plutonium was part of the effort to develop atomic bombs during World War II and therefore remained undisclosed to the public until 1946.

Plutonium derives its name from Sun System's dwarf planet Pluto. This naming is linked to the order of planets: Pluto, following Uranus and Neptune, was the next planet discovered after uranium and neptunium, and thus lent its name to the newly discovered element plutonium.

Physical and Chemical Properties of Plutonium

Plutonium is a radioactive metallic element and occurs only rarely in nature. It is almost entirely synthetic. Plutonium is produced in nuclear reactors when uranium-238 atoms absorb neutrons. The half-life of plutonium-244, the most stable isotope of plutonium, is approximately 82 million years.

Plutonium emits alpha particles, beta particles, neutrons, and gamma rays. Alpha particles are a type of radiation with short short range and can be easily stopped. However, if plutonium is inhaled or ingested, it can accumulate in the lungs and cause long-term health problems.

Plutonium Isotopes and Their Half-Lives

Plutonium has five primary isotopes: Pu-238, Pu-239, Pu-240, Pu-241, and Pu-242. All of these isotopes are fissionable, meaning they can undergo fission when struck by a neutron. Their half-lives are as follows:

Pu-238: 87.7 years

Pu-239: 24,100 years

Pu-240: 6,560 years

Pu-241: 14.4 years

Pu-242: 373,300 years

Isotopes with shorter half-lives decay more rapidly and emit higher energy radioactivity.

Plutonium - Los Alamos National Laboratory

Plutonium-238

Plutonium-238 is one of the most significant isotopes of plutonium and is particularly used in space research. This isotope provides power and heat to spacecraft through radioisotope thermoelectric generators (RTGs). The natural radioactive decay of plutonium-238 offers a long-lasting and reliable heat source.

Properties of Plutonium-238

Half-life: 87.7 years

Radiation Type: Alpha particles (low neutron and gamma radiation)

Power Density: High (produces significant heat even in small quantities)

Stability: Stable at high temperatures and retains its properties over many years.

Use in Space Missions

Plutonium-238 has played a critical role in many NASA space missions. For example:

Cassini: Spacecraft that studied Saturn and its moons.

New Horizons: Spacecraft that explored Pluto and beyond.

Perseverance: traveler exploring Mars for signs of life.

Plutonium-238 enables spacecraft to operate far from the Sun or during nighttime. It also generates the electricity needed to power the spacecraft’s scientific instruments and communication systems.

Other Applications of Plutonium

Nuclear Weapons: Plutonium-239 is a key component of nuclear weapons. One of the first atomic bombs developed during the Manhattan Project, "Fat Man," was made using plutonium-239.

Nuclear Energy: Plutonium can be used as fuel in nuclear reactors. Specifically, MOX (Mixed Oxide) fuel, composed of a mixture of plutonium and uranium oxide, is used in nuclear power plants in some countries.

Medical Applications: Plutonium-238 has been used in some heart batteries as a long-lived power source.

Technicians installing one of three Radioisotope Thermoelectric Generators (RTGs) on the Cassini spacecraft - NASA

Environmental and Medical Effects of Plutonium

As a radioactive element, plutonium poses risks to the environment and human health. When inhaled or ingested, it can accumulate in the lungs and cause long-term health problems. Therefore, the safe storage and handling of plutonium present major importance.

Plutonium-238 Production and Future Outlook

USA halted plutonium-238 production in the 1980s, but production was restarted in 2011 at the Oak Ridge National Laboratory. This production provides the plutonium required for radioisotope power systems used in NASA’s space missions. Plutonium-238 is expected to remain an indispensable source for future space exploration.