An eye for an i #429 Children

Seaborg, McMillan and the discovery of plutonium

Glenn Seaborg (left) and Edwin McMillan won the 1951 Nobel Prize for Chemistry.   | Photo Credit: Berkeley Lab/flickr

The atomic bombs dropped over Hiroshima and Nagasaki in Japan towards the end of World War II continues to divide opinion to this day. While one side argues that the use of these weapons hastened the end of the war, the other side states that the damages done with these far outweigh any gains made.

The Fat Man atomic bomb was dropped over Nagasaki on August 9, 1945. Built with a solid plutonium core, Fat Man was the second (following Little Boy that was dropped at Hiroshima on August 6, 1945) of the only two nuclear weapons that have been used in warfare. The plutonium at its core had been discovered less than five years ago. Two of its discoverers, Glenn Seaborg and Edwin McMillan, went on to win the Nobel Prize in Chemistry in 1951 “for their discoveries in the chemistry of the transuranium elements”.

California connect

Born in Michigan in 1912, Seaborg moved with his family to California at the age of 10. He did his schooling in Los Angeles, received a bachelor’s degree from the University of California, Los Angeles, in 1934, and a Ph.D in Chemistry from the University of California, Berkeley, in 1937.

McMillan was born in California in 1907 and obtained his education in that State. He attended the California Institute of Technology, where he received his B.Sc. and M.Sc. degrees, before transferring to Princeton University for his Ph.D. in 1932.

Electron shell diagram for plutonium.

Electron shell diagram for plutonium.   | Photo Credit: Greg Robson/ Wikimedia Commons

Seaborg and McMillan, along with Arthur Wahl and Joseph Kennedy, discovered plutonium in December 1940 at Berkeley, California. By bombarding uranium-238 with deuterium nuclei (alpha particles) that had been accelerated in a cyclotron device, they were able to create neptunium-238 with a half-life of two days. The neptunium produced decayed by beta emission to form plutonium-238.

"Greatest scale-up"

In a matter of months, the chemical element with atomic number 94 was conclusively identified and its basic chemistry was shown to be similar to that of uranium. Once its potential as a source of nuclear energy had been identified, its extraction was scaled up from ultramicroscopic laboratory amounts to that required for a nuclear plant. Seaborg had called it “surely the greatest scale-up factor [10 billion] ever attempted” and they succeeded at it.

While the initial amounts of the element produced was invisible to the eye, a few millionths of a gram – enough to see and weigh – had been produced by 1942. By the time the bomb exploded in Nagasaki, the Americans had several kilograms of weapons-grade plutonium.

Klaproth's way

It was on March 21, 1942 that the element was given the name plutonium. When German chemist Martin Klaproth discovered uranium, which has an atomic number 92 and is the heaviest element existing in nature, in 1789, he had named it after the planet Uranus. When McMillan discovered the element with atomic number 93, also in 1940, he had named it neptunium, after the planet Neptune. Following from the two previous elements uranium and neptunium, the element with atomic number 94 was named plutonium, after Pluto (then a planet, now a dwarf planet).

Both McMillan and Seaborg contributed immensely to the chemistry of the transuranium elements (chemical elements with atomic numbers greater than 92, the atomic number of uranium). Apart from discovering neptunium and plutonium, McMillan also contributed to the mapping of additional heavy elements and isotopes. Seaborg was not just the co-discoverer of plutonium, but all further transuranium elements up to element 102.

Powers a mission to Pluto

As for plutonium, it was first used for destruction, as already mentioned. While it is still used in making nuclear weapons, it is also indispensable in the development of nuclear power. Plutonium has also been pivotal in the Space Age as it was put to use in the Mars Curiosity Rover and the New Horizons spacecraft. When the New Horizons made its way to Pluto, plutonium – an element named after the dwarf planet – served as its source of energy.

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Printable version | May 19, 2021 2:05:47 AM | https://www.thehindu.com/children/seaborg-mcmillan-and-the-discovery-of-plutonium/article34052431.ece

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