Wed. Feb 19th, 2020

The experiment that took three years of waiting and a fire alarm



Throughout history we can find different types of scientific experiments: the surprising ones, whose results are unexpected; the intelligent ones, raised by scientists who find the right question, and the hellishly difficult ones. The discovery of the chemical element 101 of the periodic table clearly falls into the latter category.

In the mid-twentieth century, the periodic table seemed to have stabilized. It already included all the stable chemical elements found in nature, along with some elements of artificial origin, such as technetium. Elements formed by larger, but also more unstable, atoms were discovered. It was beginning to be considered impossible to find in nature any element larger than uranium, because it would have decomposed before reaching our days. For that reason, to discover new chemical elements it was necessary to create them artificially, and it was precisely at that moment when the human being discovered nuclear fusion.

Through the Manhattan project, the US government brought together its best scientists in order to create the atomic bomb. We all know the sad success of the project, but it also allowed to lay the foundations of nuclear chemistry through fission and nuclear fusion. While fission consists of breaking an unstable atom into smaller atoms, fusion is the opposite: a phenomenon that allows an atom to change its composition if it collides with another atom at sufficient speed and energy. Thus, by controlling the reaction, it was possible to add two atoms or add loose components to the nucleus of an atom. This allows to fulfill the dream of alchemy: to change one element for another, moving in the periodic table towards atoms never seen before.

Glenn Seaborg was one of the chemists who participated in the Manhattan project with his then coach Albert Ghiorsio. At the end of World War II, both settled at the University of Berkeley, where they took advantage of the newly discovered nuclear fusion to combine atoms and find new elements. The success was resounding. This couple of researchers managed to discover more chemical elements than any other person in history, being able to fill up to a sixth of the elements of the current periodic table.

Thanks to the merger, they managed to obtain between 1946 and 1953 for the first time the elements of atomic number 94 (plutonium), 95 (americium), 96 (curium), 97 (berkelium), 98 (californium), 99 (einsteinium) and 100 (fermium) All in a span of seven years, forcing to update the periodic tables of textbooks annually, unfortunately for teachers and publishers. Thanks to this first round of discoveries, in 1951, Seaborg won the Nobel Prize in Chemistry and his team received the nickname “element hunters”.

But the streak ended when trying to achieve the element with the atomic number 101.

The time trial experiment

The problem was the instability of the atoms with which they began to work. To advance in the periodic table towards new elements, the method that worked best was to bombard an atom with helium ions, also called “alpha particles”. If these ions are fired with sufficient power, they can be integrated into the nucleus of another atom, becoming the element located two squares to the right in the periodic table. For this reason, in order to achieve element 101, it was necessary to use element 99: einsteinium.

But Seaborg and his team knew that Einsteinium was unstable, and that its atoms could hold from a few seconds to a year before breaking into other smaller atoms. If they wanted a sufficient amount of einsteinium for the experiment, the only method was to bombard a sample of plutonium with neutrons continuously and uninterruptedly for three years.

In addition, due to the conditions of the bombardment and the availability of plutonium, the team would only be able to obtain a single sample of einsteinium for the experiment. If something went wrong, I would have to wait another three years to get new samples. All good.

The next step was to place the einsteinium sample on a gold foil while it was bombarded with the helium ions. In about ten minutes the gold foil dissolved and, if everything worked correctly, the helium ions will have entered the einsteinium nucleus, forming element 101. The problem is that there are so few einsteinium atoms that leave decomposing over time, it is not easy to predict whether the crash will be effective. Chemists could make their best estimates, but there was a luck component impossible to predict with their instruments. For this reason they tried to ensure that at least a few atoms came to form element 101, bringing together all the possible einsteinium.

The decisive step was to demonstrate that the new element had really been generated. Considering that only a few atoms would be achieved, it would be impossible to prove it through a chemical reaction, so the only method available was to let the new element decompose and study its remains. The problem is that the necessary particle detector was in another building several kilometers away, and it was necessary to arrive at the time of disintegration, just after the gold foil dissolves. That is, approximately ten minutes.

The idea of ​​having to wait three years if they failed caused the experiment to be planned as a bank robbery. It was going to be dark, to avoid any jamming that spoiled the sample. After bombing the einsteinium in the laboratory, Ghiorsio would wait with his car with the engine running at the door, and the youngest of the team would make a relay race to go from the laboratory to the detector, accelerating as much as possible without overturning the sample. They practiced for several nights with false samples, looking for the best routes and the best runners, using stopwatches to ensure they arrive on time. They had time while the Einsteinium formed.

On a February night in 1955 they performed their choreography with the real sample. There was no setback. No traffic jam at night. Nothing they could blame if something had gone wrong. The letters were drawn and it was a matter of waiting to see if they had the new element or if they should repeat the experiment three years later.

Since the experiment would last through the night and the stress of the moment was going to dent, Ghiorsio connected the building’s fire alarm to the detector. So they could take advantage and stay in the dining room quietly, waiting for the sound of the alarm as if they were the chimes of the new year, with nervousness and fear that the sound would never come.

The combination of preparation and luck paid off and, finally, they managed to create element 101 at first. The fire alarm rang seventeen times, indicating the number of atoms they managed to form. Enough to make it worth it.

Seaborg, Ghiorsio and his team shouted and celebrated the sound of fire alarms with champagne in the dining room. They decided to baptize the new element as Mendelevian, in homage to Dmitri Mendeleev, The creator of the periodic table. This did not suit the United States at all, as it meant paying tribute to a Russian scientist during the cold war. But the team kept their decision, wanting to show that science really knows no boundaries. And especially during such complicated experiments.

DON’T KEEP IT UP:

  • Mendelevium, Einsteinium and other heavy elements of the periodic table do not have a real commercial application, since they are so unstable that their atoms do not remain long enough. They have a very important use, however, in basic research on atomic structure.
  • The list of elements indicated in the article includes only the period of time prior to the discovery of the mendelevio. After that publication, the Searborg and Guiorso team managed to discover the Nobel (item 102). Later, Ghiorso participated in the discovery of Lawrencio (103), Rutherfordio (104), Dubnio (105) and Seaborgio (106). The latter is named after Seaborg.

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