The Manhattan Project

The Element Hunters: The Discovery of Mendelevium

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The Element Hunters: The Discovery of Mendelevium

Using footage found in the Lawrence Berkeley National Laboratory, former Director of Operations and Development at the 88-Inch Cyclotron Claude Lyneis put together a video describing the discovery of element 101, mendelevium. Narrated by Lyneis, the video shows the tools and techniques used in the discovery of heavy elements after the war, and provides a brief history of the search for mendelevium. This dramatically indicates the speed and skill necessary to perform these groundbreaking experiments. The discovery of mendelevium involved a team from the Rad Lab including Glenn Seaborg and Albert Ghiorso. Seaborg and Ghiorso helped discover over a dozen elements in addition to mendelevium, helping to further our understanding of the nature of matter.
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[Many thanks to Claude Lyneis for donating this footage to the Atomic Heritage Foundation.]

Claude Lyneis: On November 1, 1952, Operation Ivy Mike detonated the first hydrogen bomb in the South Pacific. A monster ten-megaton blast, it created a huge radioactive cloud, which rose to 130,000 feet with a twenty-mile-wide stem. U.S. Air Force F-84 Thunderjets flew into that cloud to sample the radioactive components. Flying through the stem of the cloud, air filters on the jets picked up radioactive debris from the explosion, which was sent to U.S. labs for analysis.

The Rad Lab in the Berkeley hills was one of the labs to get access to the samples of the bomb debris. A group of chemists and physicists at the lab had already discovered several new elements—including plutonium, americium, and californium—all of which have important practical applications.

Albert Ghiorso and his colleagues discovered two new elements that were created in the blast: element 99, einsteinium, and element 100, fermium. To search for the next element, they came up with a plan to use a 60-inch cyclotron located on the Berkeley campus. The idea was to convert element 99 into element 101 using alpha particles accelerated to forty-eight million electron volts in the cyclotron.

The first step was to produce a microscopic quantity of einsteinium in the core of the Idaho Falls reactor by neutron irradiation of plutonium slugs. The highly radioactive plutonium was delivered in a shielded box to the Radiation Laboratory in Berkeley for chemical separation.

The work was performed in special caves with thick shielding and lead-glass windows to protect the workers from the intense radiation coming from the irradiated materials. With fairly simple remote tools, it took great skill to perform the many steps required to safely extract the einsteinium from the plutonium slugs.

Concentrated hydrochloric acid was used to dissolve the plutonium and other heavy metals as the first step. This produced a few liters of a radioactive brew that they hoped contained a few billion atoms of element 99 to make a target. This was followed by several more chemical steps—including using a centrifuge, precipitation, and ion exchange columns—to produce a purified sample of einsteinium.

In the last step, the einsteinium was electroplated onto a thin foil that would serve as a target for the cyclotron bombardment. The sample was turned over to Al Ghiorso to determine how much einsteinium was on the target by measuring its radioactive decay properties.

For the cyclotron bombardment, Ghiorso had developed a new target-catcher system to capture the atoms of the new element on a gold foil when the alpha particles fused with the einsteinium atoms. The 60-inch cyclotron, developed by Ernest Lawrence, weighed 200 tons and used powerful electromagnets to bend the alpha particles in a spiral orbit as they were accelerated to high energy. After a three-hour bombardment, researchers Ghiorso and Harvey enter the cyclotron vault to extract the gold foil. It’s a race to detect the element with its short half-life before it decays away and vanishes.

Ghiorso fires up his VW Bug with its supercharged engine and they race off the Berkeley campus and up to the Rad Lab chemistry building about one mile away. Team leader Stanley Thompson begins the final chemistry needed to separate the atoms of the new element from the target. The atoms of the various heavy metals move down the ion exchange column at different rates and form predictable bands. Each droplet can them be analyzed and its relative atomic number calculated.

An ion chamber that can detect the fission of a single atom is used to search for the telltale signal of element 101. After repeating the experiment eight times, a total of seventeen atoms of the new element 101 are detected.

The researchers name element 101 mendelevium in their paper published in the June ’55 edition of Physical Review Letters. This was the last new element created using Lawrence’s 60-inch cyclotron. Albert Ghiorso continued the hunt for new element using a new linear accelerator and discovered five more elements at Berkeley.