Plutonium is a radioactive element which was produced in 1940. It is used as fuel in nuclear power reactors and to power aircraft. It is also used to make an atomic bomb.
History and Discovery
Plutonium is a synthetic element and was produced and isolated in University of California, Berkeley. In 1940, Glenn T. Seasborg, Joseph W. Kennedy, Edwin McMillan and Arthur Wahl at Berkeley Radiation Laboratory, bombarded deuteron on an isotope of uranium in the 60-inch cyclotron, which created neptunium-238. Neptunium-238 has a half-life of little over two days and decay by beta emission forming the element 94 [1]. Due to world war the declaration of the discovery of new element was delayed until after the war. The element 94 was suggested to be named after the planet Pluto, following the tradition of naming the previous two planets after the planets of our galaxy, i.e. uranium after Uranus and neptunium after Neptune. Pluto was considered a planet of our milky way at that time, the next planet after Neptune.
Plutonium
| Periodic Table Classification | Group n/a Period 7 |
|---|---|
| State at 20C | Solid |
| Color | Silvery white |
| Electron Configuration | [Rn] 5f6 7s2 |
| Electron Number | 94 |
| Proton Number | 94 |
| Electron Shell | 2, 8, 18, 32, 24, 8, 2 |
| Density | 19.84 g.cm-3 at 20°C |
| Atomic number | 94 |
| Atomic Mass | 244.00 g.mol -1 |
| Electronegativity according to Pauling | 1.28 |
Occurrence
Plutonium was discovered as a synthetic element. Only minor traces of plutonium occur naturally. It is commonly found in concentrated ores of uranium. Plutonium is formed in ores when U-238 undergoes spontaneous fission emitting energized neutrons which upon striking with nucleus of another U-238 atom is absorbed by it, making U-239 in the process. U-239 has short half-life and it decays into Np-239 which then decays to form Pu-239. Plutonium isotope Pu-244 has a long half-life of approximately 80 million years even then it is believed that all primordial form of the element on earth has decayed forming other elements [2]. It is produced only in supernovae and because of its half-life, which is longer than any other transuranic element, interstellar Pu-244 traces can be found in the deep-sea floor. Major source of plutonium for commercial uses is the burning of uranium in nuclear reactors. Since separation of plutonium isotope is difficult and expensive only particular isotopes are manufactured as per requirement.
Physical Characteristics
Plutonium appears silver grey in colour. It tarnishes if exposed to air forming a dull coating on itself, while in humid air it expands forming hydrides and oxides. The powdered form of plutonium is pyrophoric. It has six allotropic forms. Plutonium allotropes have different densities and structures but have same internal energy making it sensitive to temperature and pressure changes [3]. This sensitivity to outer environment allows for dramatic volume changes and phase transitions from one form to another. This makes it difficult to machine.
Chemical Characteristics
Plutonium appears silver grey in colour. It tarnishes if exposed to air forming a dull coating on itself, while in humid air it expands forming hydrides and oxides. The powdered form of plutonium is pyrophoric. It has six allotropic forms. Plutonium allotropes have different densities and structures but have same internal energy making it sensitive to temperature and pressure changes [3]. This sensitivity to outer environment allows for dramatic volume changes and phase transitions from one form to another. This makes it difficult to machine.
Significance and Uses
- Due to its ease of fission, plutonium is used as fissile component for nuclear weaponry. And the critical mass of plutonium is about a third of uranium so very little quantity of plutonium can be used to make atomic bomb.
- Plutonium is used as fuel in commercial nuclear power reactors.
- Plutonium-238 is used in radioisotope heater units and radioisotope thermoelectric generators since it emits large amount of thermal energy making it well suited for devices that do not need direct maintenance for a long time [3].
- Artificial heart pacemakers are powered by plutonium (Pu-238).
- It is also used to generate neutrons for research purposes.
- Plutonium is used as the power source for space crafts.
Health Hazards
Plutonium is radioactive element. It is also a toxic element. It is dangerous to handle since it can accumulate in bone / bone marrow. World is contaminated by plutonium oxide due to the extensive nuclear tests all around the world and some major nuclear accidents in our history.
If ingested, only small amount of plutonium will be absorbed by the body but it still can be dangerous. If inhaled, the lungs and liver are prone to diseases like cancer. Large quantity of inhaled plutonium or ingested plutonium will eventually irradiate internal human organs. Long term exposure to ionizing radiation released by plutonium can cause genetic damage, cancer, radiation sickness and even death. Metallic plutonium in finely divided form is also a fire hazard.
Isotopes of Plutonium
Plutonium has twenty known radioisotopes. Plutonium isotopes range in mass number from 228 to 247. Traces of plutonium isotopes Pu-238, Pu-239, Pu-240 and Pu-244 can be found naturally. Pu-244 has the longest half-life [4]. Pu-239 is the most abundantly existing isotope of plutonium, since it is purposefully manufactured for nuclear reactors and also for nuclear weaponry.
REFERENCES
[1]. Seaborg, Glenn T.; McMillan, E.; Kennedy, J. W.; Wahl, A. C. (1946). “Radioactive Element 94 from Deuterons on Uranium”. Physical Review. 69 (7–8): 366
[2]. Hecker, Siegfried S. (2000). “Plutonium and its alloys: from atoms to microstructure” (PDF). Los Alamos Science. 26: 290–335. Retrieved February 15, 2009.
[3]. Hecker, Siegfried S.; Martz, Joseph C. (2000). “Aging of Plutonium and Its Alloys” (PDF). Los Alamos Science. Los Alamos, New Mexico: Los Alamos National Laboratory (26): 242. Retrieved February 15, 2009.
[4]. Kennedy, J. W.; Seaborg, G. T.; Segrè, E.; Wahl, A. C. (1946). “Properties of Element 94”. Physical Review. 70 (7–8): 555–556.