In the history of human civilisation, no scientific discovery exploded in the face of mankind as did plutonium-239. The element was produced for the first time on March 28, 1941 at the Lawrence Berkeley Laboratory in California by a team of physicists and chemists led by Glenn T. Seaborg, the 1951 Chemistry Nobel Laureate. It was the realisation of an alchemists’ dream of large-scale transmutation, a synthetic element produced by human being.
Seaborg submitted the paper on their discovery to the journal Physical Review, but the paper was not accepted after it was assumed that plutonium may be used to build an atomic bomb. The existence of plutonium was nonetheless loudly announced to the world by the nuclear bomb dropped over Nagasaki on August 9, 1945. Thus, plutonium came into existence as a lethal weapon-grade material. Also, the discoverers of plutonium were allowed to publish their findings after the war ended.
Plutonium-239 is a highly radioactive element. A radioactive element disintegrates emitting energetic nuclear particles and radiation. The potency of a radioactive material is determined not only by the radiation it emits but also by its half-life. A radioactive material that emits alpha particle is highly hazardous, if it is inhaled or ingested. On the other hand, materials which emit penetrating x-rays and gamma rays are hazardous even at large distances as these radiations can travel large distances in air and irradiate the whole body. The time period over which the radioactive material remains hazardous is determined by its half-life. The half-life is the time period over which the activity decays to half of its original value. A radioactive material with short half-lives will become relatively harmless in a short period of time. On the other hand, a material with long half-life will remain radioactive for a long period of time. The significant parameter from hazardous point of view is the specific activity – activity in unit mass of the substance.
Plutonium has 20 isotopes – nuclei with the same number of protons but different number of neutrons. The longest-lived is plutonium-244, with a half-life of 80.8 million years. Two other isotopes with long half-life are plutonium-239, with a half-life of 24,100 years and plutonium-242, with a half-life of 374,000 years. All of the remaining isotopes have half-life that are less than 7,000 years.
All the isotopes of plutonium are primordial elements, meaning they existed (albeit in low concentrations) since the Earth was formed 4.55 billion years ago. However, since their half-life is much less than the age of the Earth, nearly all of them had decayed into lighter elements by now. Nonetheless, small traces of plutonium-239, a few parts per trillion, were found in some uranium ores, such as the natural reactor in Oklo, Gabon. In 1971, trace quantities of plutonium-244 were discovered in Precambrian-era phosphate in southern California.
Currently, most of the plutonium found in the Earth’s environment resulted from human activities, in particular, from the now banned atmospheric testing of nuclear weapons in the 1950s. It is estimated that since 1945, about 7,700 kg has been released through nuclear explosions. As there are no natural sources of plutonium, all of the plutonium presently in stock throughout the world is produced in commercial power reactors, as well as in special purpose reactors designed for weapons production.
Plutonium-239 decays by emitting alpha particles, which is the helium nucleus. External exposure to alpha particles isn’t much of a health risk. Because of their low penetration, they are stopped by the outer layer of the skin. But they are highly dangerous if inhaled. They cause damage to DNA, which, in turn, increases the risk of cancer. Plutonium-239 in the atmosphere can enter our body through body wounds. Once inside, it remains within the body for a long period of time and irradiate the body organs and tissues by the emission of alpha particles. It is, however, eliminated from the body very slowly through excretion. It may take around 30 to 50 years for plutonium to become biologically insignificant within our body.
The adverse effects of plutonium on the environment are not that alarming. They may enter the soil and groundwater from accidental releases and improper disposal of wastes from a nuclear reactor. Soil can also become contaminated through fallout during underground nuclear weapons testing. Plants absorb plutonium, but the levels are not high enough to cause bio magnification of plutonium up the food chain, or accumulation in the bodies of animals.
Besides using it to make nuclear weapons, plutonium is used for some peaceful purposes too. Along with uranium-235 and uranium-233, plutonium-239 as well as plutonium-241 is used as fuel in reactors at commercial nuclear power plants.
Nuclear powered cardiac pacemakers use plutonium-238 batteries. They can keep the heart ticking for up to 30 years, much longer than pacemakers using lithium-iodine cell batteries which last anywhere from about five to 12 years. When one of these patients dies, the pacemaker is removed and shipped to Los Alamos National Laboratory where the plutonium is recovered. People using plutonium-powered pacemakers are still alive though.
The US space agency NASA has used this isotope of plutonium to power its space instruments– all the way from the experiments for the Apollo lunar missions to the deep-space probes, such as the Pathfinder, Pioneer, Voyager, New Horizons and Cassini.
Today, plutonium serves as an explosive ingredient in tens of thousands of nuclear weapons in the possession of a Superpower led by a person with questionable mental stability and a rogue nation with an enigmatic and unpredictable leader. There is a high risk that these two men may unleash this weapon of mass destruction and annihilate not only each other but also the whole of mankind.
- The writer, Quamrul Haider, is a Professor of Physics at Fordham University, New York