Doubts linger over who discovered dubnium

The story of the discovery of dubnium is one that is shrouded in controversy. Both the Soviet Joint Institute of Nuclear Research and the American Lawrence Berkeley Laboratory laid claim to the discovery around the same time. A.S.Ganesh describes the circumstances surrounding the discovery and naming of the element dubnium...

Discoveries are often built upon the work of many others. Sometimes the final act occurs in isolation and sometimes they occur at different places simultaneously by groups or individuals working separately. But more often than not, it is possible to attribute the discovery correctly to the ones it belongs to. When that isn’t the case, however, it almost always leads to confusion.

The discovery of dubnium is one such instance where it still isn’t clear as to who actually discovered it. A chemical element with the atomic number 105 and the atomic symbol Db, dubnium is a synthetic element about which little is known. Dubnium-268, with a half-life of about 30 hours, is the most stable isotope known as of now. The element has no uses currently outside basic research as only trace quantities have ever been produced.

The two claims

The discovery of the element 105 was first reported in April 1968 by a team from the Joint Institute of Nuclear Research (JINR) in Dubna, now in Russia. Led by Soviet nuclear physicist Georgy Flerov, they succeeded by bombarding americium-243 with ions of neon-22, producing very small quantities of dubnium-260 and dubnium-261 in the process.

By the end of April 1970, scientists at the Lawrence Berkeley Laboratory (LBL) in Berkeley, the U.S. were able to produce element 105 of their own. While their attempts to duplicate the Soviet experiment had failed, American nuclear scientist Albert Ghiorso and his colleagues achieved success by bombarding a californium-249 target using nitrogen-15 ions.

How to name it

Both sides laid claim to the discovery of the element 105. While the Soviets believed that they were the first to synthesise it and hence the rightful discoverers, the Americans cited reports that the Soviet methods couldn’t be reproduced and implied that their synthesis thereby should receive priority. The situation only became more murky when the two sides tussled over the rights to name the element.

The Soviet side proposed the name nielsbohrium (Ns) in honour of the Danish nuclear physicist Niels Bohr, best-known for his work in understanding the atomic structure and quantum theory. The Americans, meanwhile, suggested hahnium (Ha) after German chemist Otto Hahn, the discoverer of nuclear fission and a pioneer in the fields of radioactivity and radiochemistry.

By the mid-1970s, the naming controversy mushroomed to a stage where an international group of physicists and chemists, referred to as the joint neutral group, were formed to try and solve problems surrounding the discovery of super-heavy elements. In an effort to render this unnecessary, leading scientists from both organisations decided to meet on the sidelines of a seminar.

A meeting in Russia

In September 1975, American chemist Glenn Seaborg and Ghiorso travelled to Dubna, where they had a two-hour meeting with Flerov, nuclear physicist Yuri Oganessian and other Soviet scientists. While the transcript of this meeting gives us an insider’s view of how scientists involved tried to solve the disputes related to the discoveries of the elements 104 and 105 amongst themselves, without resorting to an outside group, it eventually proved unsuccessful.

By 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed a Joint Working Party to resolve the issues pertaining to controversial elements. They finished their work by 1991 and the results were published in 1993.

The report stated that the first definitely successful experiment producing element 105 was that of the LBL in April 1970, followed closely by JINR’s June 1970 experiment. As a result, it was concluded that the discovery of element 105 should be shared by both teams.

As for the name of the element, IUPAC had a list of names by 1996 and also accepted more recommendations. In the end, in 1997, element 105 was named dubnium, after Dubna. The verdict might be out, but the credit for the discovery of dubnium continues to be controversial.

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What about atomic weights?

The atomic weight of naturally occurring elements is calculated by averaging the weights of the natural abundances of the different isotopes of the concerned element.

Human-made transuranium elements, however, don’t occur naturally and hence have no natural abundance for their isotopes.

In these cases, therefore, the IUPAC convention is to list the atomic weight of the longest-lived isotope in the periodic table.

As a new isotope of these elements with a longer half-life can be produced any time in the future, the atomic weights of human-made transuranium elements in the periodic table should only be considered as provisional.