In the history of human civilisation, no scientific discoveries 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 Seaborg, the 1951 Chemistry Nobel Laureate. It was the realisation of an alchemist’s dream of large-scale transmutation, a synthetic element produced by man.
Seaborg submitted a paper on their discovery to the journal Physical Review, but the paper was not published after it was determined that plutonium may be used to build an atomic bomb. The existence of plutonium was nevertheless 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 highly radioactive. A radioactive elementdisintegrates quickly emitting energetic particles or radiation. The potency of a radioactive element is determined by its half-life– the time required for half of the atoms in a sample to decay. Elements with half-life less than a year do not pose health risks because they become harmless in short order. Those with very long half-life, eg millions of years, are also of little concern because they emit radiation at a negligible rate. The radioactive elements with half-life somewhere between these broad limits are the ones that are dangerous. As a rule, it generally takes about ten half-lives for a radioactive nucleus to be considered safe.
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 have existed 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 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 helium nucleus. External exposure to alphas isn’t much of a health risk. Because of their low penetration depth, alphas are stopped by the skin. But they are highly dangerous if inhaled. They cause damage to DNA, which, in turn, boosts the risk of cancer.
Plutonium-239 in the atmosphere can enter our body through open wounds. Once inside, it is eliminated from the body very slowly, through excretion. It takes around 20-50 years for plutonium to be biologically removed from 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 isused for some peaceful purposes, too.Along with uranium-235 and uranium-233, plutonium-239 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 upto 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 Super Power led by a person with questionable mental stability and a rogue nation with an enigmatic and unpredictable leader. There is too large a probability that these two men will unleash this weapon of mass destruction and annihilate not only each other but also the rest of mankind. n

The writer is a Professor of Physics at Fordham University, New York. The article is based on a talk given by him on the 75th anniversary of the isolation
of plutonium.

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