Nuclear Friday: The Antacid of Alchemy

When Lise Meitner and Otto Hahn began their research project that led to the discovery of nuclear fission they weren’t trying to discover nuclear fission. The were instead trying to perform a sort of alchemy, the transmutation of one element into another. Radioactive decay was already understood by then as a type of spontaneous natural alchemy. Alpha emission reduces an element’s atomic number by two. Beta decay transforms a neutron into a proton, thus moving an element one place up on the periodic table. Moving downward isn’t so interesting, but if a heavy element were induced to move upward it would be possible to create previously unknown elements.

Enrico Fermi was the first to make a serious effort at creating an unknown element heavier than Uranium. He thought that by bombarding Uranium, element 92, with neutrons moving at just the right speed, the nuclei would absorb neutrons and subsequently beta decay twice, becoming a newly discovered element 94. Fermi had even picked out a new name for his element, Hesperium, after the ancient Greek name for Italy. For a while Fermi maintained that he really had discovered Hesperium, but chemical analysis of his samples were inconclusive. Italy and the Evening Star lost their chance to get on the periodic table, though Fermi himself would get a spot on the Table later on.

Lise Meitner attended a conference Fermi gave about the interesting but inconclusive results of his experiments. Meitner believed at the time that Fermi probably really had synthesized element 94. She also thought she could succeed where he had failed. With the resources available at the Kaiser Wilhelm Institute and skill in experimental design, she expected to confirm element 94 quickly. Meitner also had the advantage of her longtime research associate Otto Hahn, the most successful nuclear chemist of the 1930’s. Hahn would be able to coax out even the smallest amounts of element 94 from Meitner’s samples.

Meitner and Hahn failed to make 94. Hahn would eventually establish that no element 94 was created and that instead Uranium was splitting into Barium and Krypton while releasing a large amount of energy. Meitner had been forced to abandon her work by this time, but she and her nephew, Otto Frisch, would publish a theoretical analysis of Hahn’s results that suggested that an atomic bomb was possible. I’ve written in detail about this here.

The original concept for atom bombs was that they would have to be very large. The British Tube Alloys research group initially thought that a bomb would require twelve tons of Uranium. The Einstein-Szilard letter to FDR suggested that a bomb would have to be delivered by submarine and be pretty much the size of a submarine. This is obviously a serious limitation in weapon design. Everyone wanted something small enough to drop from an aircraft. Otto Frisch, who was working for Tube Alloys, proved that if Uranium were enriched to a high proportion of the U-235 isotope it would be possible to create a much lighter bomb. Everyone knew that separating Uranium isotopes would be a slow and costly process. The nuclear alchemy of element 94 seemed like it might be a more quicker and cheaper path to a practical nuclear weapon.

Shortly before this time the synthesis of element 94 had been confirmed by Glenn Seaborg’s team at UC Berkeley. They accelerated deuterium nuclei in the cyclotron in this post’s title background image and shot them into a sample of Uranium. Deuterium has one proton and neutron. The Uranium nucleus absorbed these particles and became element 93. As predicted by Fermi years earlier, element 93 was unstable and transformed into element 94 by beta decay. Seaborg proposed the names Neptunium and Plutonium for these elements after the order of the planets. These names would not become official until after WWII.

While Seaborg had confirmed that Plutonium synthesis was possible his method of shooting deuterons out of a cyclotron into thin foils of uranium was not scalable into an industrial process capable of making the tens of kilograms needed for just one nuclear weapon. Something similar to Fermi’s initial concept of using just neutrons really needed to be possible. And why shouldn’t it be possible to just happen naturally inside a nuclear reactor using slightly enriched Uranium and heavy water or graphite as a neutron moderator? Fermi, who had moved to the US in the late 1930’s, would prove that it was by building a test reactor at Oak Ridge. Full scale production began at Hanford, Washington which would produce four plutonium cores by the end of the war, including the cores for Gadget and Fat Man.

The nuclear alchemy of element 94 has been a part of the large majority of all the nuclear weapons, only the US, China, South Africa, and Israel have ever made enriched uranium devices, and only China operates any to this day.

So What about Antacids?

Yes! What about them? Oh, after WWII, most of the scientists working on military programs returned to civilian research jobs. And what better way for a physics department to gain prestige than to synthesize a new element and name it after itself? Most of this research followed Seaborg’s method of whacking a light nucleus into a heavy one and seeing what comes out. Seaborg himself did a lot of this and eventually got an element named after him.

The research has continued to this day, heavier and heavier “bullet” nuclei have been required, but most heavier bullets cause spallation in their target nuclei. So far the heaviest element ever synthesized is element 118, recently named Oganesson. It was created in Dubna, Russia using what is probably the most perfect bullet for heavy element synthesis, Calcium 48.

relief2
Price: Six Million Dollars

They make the world’s most expensive calcium carbonate in Dubna. I estimate that a pack of Rolaids like this one would cost at least six million of it was made with Dubna’s special isotopically pure blend. Remember, isotope separation is always expensive, and the more stable isotopes an element has, the harder it is to get its rare isotopes.

Calcium has eight stable isotopes. I’ll let Sir Martyn of Nottingham explain why Calcium 48 is so important.

That little vial has about a twelfth the amount of calcium carbonate as there is in a pack of Rolaids. As the video mentions, Dubna is not going to be able to use their magic calcium to go beyond element 118. They are investigating heavier bullets, but none is as promising as their special calcium. Dubna has also considered using a heavier target, such as Einsteinium, but that element is synthesized only at Oak Ridge, and the price is out of reach.

If you are interested in all four of the elements recognized and named within the last year I recommend this review from Martyn Poliakoff.

Now that there’s no more for Calcium 48 left to do, it will likely be a long time before we have any more nuclear alchemy.

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