Dubnium

Dubnium is a synthetic chemical element; it has symbol Db and atomic number 105. It is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of about 16 hours. This greatly limits extended research on the element.
Dubnium does not occur naturally on Earth and is produced artificially. The Soviet Joint Institute for Nuclear Research claimed the first discovery of the element in 1968, followed by the American Lawrence Berkeley Laboratory in 1970. Both teams proposed their names for the new element and used them without formal approval. The long-standing dispute was resolved in 1993 by an official investigation of the discovery claims by the Transfermium Working Group, formed by the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics, resulting in credit for the discovery being officially shared between both teams. The element was formally named dubnium in 1997 after the town of Dubna, the site of the JINR.
Theoretical research establishes dubnium as a member of group 5 in the 6d series of transition metals, placing it under vanadium, niobium, and tantalum. Dubnium should share most properties, such as its valence electron configuration and having a dominant +5 oxidation state, with the other group 5 elements, with a few anomalies due to relativistic effects. A limited investigation of dubnium chemistry has confirmed this.

Introduction

Discovery

Background

, element 92, is the heaviest element to occur in significant quantities in nature; heavier elements can only be practically produced by synthesis. The first synthesis of a new element—neptunium, element 93—was achieved in 1940 by a team of researchers in the United States. In the following years, American scientists synthesized the elements up to mendelevium, element 101, which was synthesized in 1955. From element 102, the priority of discoveries was contested between American and Soviet physicists. Their rivalry resulted in a race for new elements and credit for their discoveries, later named the Transfermium Wars.

Reports

The first report of the discovery of element 105 came from the Joint Institute for Nuclear Research in Dubna, Moscow Oblast, Soviet Union, in April 1968. The scientists bombarded ²⁴³Am with a beam of ²²Ne ions, and reported 9.4 MeV and 9.7 MeV alpha activities followed by alpha activities similar to those of either ²⁵⁶103 or ²⁵⁷103. Based on prior theoretical predictions, the two activity lines were assigned to ²⁶¹105 and ²⁶⁰105, respectively.
After observing the alpha decays of element 105, the researchers aimed to observe spontaneous fission of the element and study the resulting fission fragments. They published a paper in February 1970, reporting multiple examples of two such activities, with half-lives of 14 ms and. They assigned the former activity to ^242mfAm and ascribed the latter activity to an isotope of element 105. They suggested that it was unlikely that this activity could come from a transfer reaction instead of element 105, because the yield ratio for this reaction was significantly lower than that of the ^242mfAm-producing transfer reaction, in accordance with theoretical predictions. To establish that this activity was not from a reaction, the researchers bombarded a ²⁴³Am target with ¹⁸O ions; reactions producing ²⁵⁶103 and ²⁵⁷103 showed very little SF activity, and the reaction producing heavier ²⁵⁸103 and ²⁵⁹103 produced no SF activity at all, in line with theoretical data. The researchers concluded that the activities observed came from SF of element 105.
In April 1970, a team at Lawrence Berkeley Laboratory, in Berkeley, California, United States, claimed to have synthesized element 105 by bombarding californium-249 with nitrogen-15 ions, with an alpha activity of 9.1 MeV. To ensure this activity was not from a different reaction, the team attempted other reactions: bombarding ²⁴⁹Cf with ¹⁴N, Pb with ¹⁵N, and Hg with ¹⁵N. They stated no such activity was found in those reactions. The characteristics of the daughter nuclei matched those of ²⁵⁶103, implying that the parent nuclei were of ²⁶⁰105.
These results did not confirm the JINR findings regarding the 9.4 MeV or 9.7 MeV alpha decay of ²⁶⁰105, leaving only ²⁶¹105 as a possibly produced isotope.
JINR then attempted another experiment to create element 105, published in a report in May 1970. They claimed that they had synthesized more nuclei of element 105 and that the experiment confirmed their previous work. According to the paper, the isotope produced by JINR was probably ²⁶¹105, or possibly ²⁶⁰105. This report included an initial chemical examination: the thermal gradient version of the gas-chromatography method was applied to demonstrate that the chloride of what had formed from the SF activity nearly matched that of niobium pentachloride, rather than hafnium tetrachloride. The team identified a 2.2-second SF activity in a volatile chloride portraying eka-tantalum properties, and inferred that the source of the SF activity must have been element 105.
In June 1970, JINR made improvements on their first experiment, using a purer target and reducing the intensity of transfer reactions by installing a collimator before the catcher. This time, they were able to find 9.1 MeV alpha activities with daughter isotopes identifiable as either ²⁵⁶103 or ²⁵⁷103, implying that the original isotope was either ²⁶⁰105 or ²⁶¹105.

Naming controversy

JINR did not propose a name after their first report claiming synthesis of element 105, which would have been the usual practice. This led LBL to believe that JINR did not have enough experimental data to back their claim. After collecting more data, JINR proposed the name bohrium in honor of the Danish nuclear physicist Niels Bohr, a founder of the theories of atomic structure and quantum theory; they soon changed their proposal to nielsbohrium to avoid confusion with boron. Another proposed name was dubnium. When LBL first announced their synthesis of element 105, they proposed that the new element be named hahnium after the German chemist Otto Hahn, the "father of nuclear chemistry", thus creating an element naming controversy.
In the early 1970s, both teams reported synthesis of the next element, element 106, but did not suggest names. JINR suggested establishing an international committee to clarify the discovery criteria. This proposal was accepted in 1974 and a neutral joint group formed. Neither team showed interest in resolving the conflict through a third party, so the leading scientists of LBL—Albert Ghiorso and Glenn Seaborg—traveled to Dubna in 1975 and met with the leading scientists of JINR—Georgy Flerov, Yuri Oganessian, and others—to try to resolve the conflict internally and render the neutral joint group unnecessary; after two hours of discussions, this failed. The joint neutral group never assembled to assess the claims, and the conflict remained unresolved. In 1979, IUPAC suggested systematic element names to be used as placeholders until permanent names were established; under it, element 105 would be unnilpentium, from the Latin roots un- and nil- and the Greek root pent-. Both teams ignored it as they did not wish to weaken their outstanding claims.
In 1981, the Gesellschaft für Schwerionenforschung in Darmstadt, Hesse, West Germany, claimed synthesis of element 107; their report came out five years after the first report from JINR but with greater precision, making a more solid claim on discovery. GSI acknowledged JINR's efforts by suggesting the name nielsbohrium for the new element. JINR did not suggest a new name for element 105, stating it was more important to determine its discoverers first.
In 1985, the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics formed a Transfermium Working Group to assess discoveries and establish final names for the controversial elements. The party held meetings with delegates from the three competing institutes; in 1990, they established criteria on recognition of an element, and in 1991, they finished the work on assessing discoveries and disbanded. These results were published in 1993. According to the report, the first definitely successful experiment was the April 1970 LBL experiment, closely followed by the June 1970 JINR experiment, so credit for the discovery of the element should be shared between the two teams.
LBL said that the input from JINR was overrated in the review. They claimed JINR was only able to unambiguously demonstrate the synthesis of element 105 a year after they did. JINR and GSI endorsed the report.
In 1994, IUPAC published a recommendation on naming the disputed elements. For element 105, they proposed joliotium after the French physicist Frédéric Joliot-Curie, a contributor to the development of nuclear physics and chemistry; this name was originally proposed by the Soviet team for element 102, which by then had long been called nobelium. This recommendation was criticized by the American scientists for several reasons. Firstly, their suggestions were scrambled: the names rutherfordium and hahnium, originally suggested by Berkeley for elements 104 and 105, were respectively reassigned to elements 106 and 108. Secondly, elements 104 and 105 were given names favored by JINR, despite earlier recognition of LBL as an equal co-discoverer for both of them. Thirdly and most importantly, IUPAC rejected the name seaborgium for element 106, having just approved a rule that an element could not be named after a living person, even though the 1993 report had given the LBL team the sole credit for its discovery.
In 1995, IUPAC abandoned the controversial rule and established a committee of national representatives aimed at finding a compromise. They suggested seaborgium for element 106 in exchange for the removal of all the other American proposals, except for the established name lawrencium for element 103. The equally entrenched name nobelium for element 102 was replaced by flerovium after Georgy Flerov, following the recognition by the 1993 report that that element had been first synthesized in Dubna. This was rejected by American scientists and the decision was retracted. The name flerovium was later used for element 114.
In 1996, IUPAC held another meeting, reconsidered all names in hand, and accepted another set of recommendations; it was approved and published in 1997. Element 105 was named dubnium, after Dubna in Russia, the location of the JINR; the American suggestions were used for elements 102, 103, 104, and 106. The name dubnium had been used for element 104 in the previous IUPAC recommendation. The American scientists "reluctantly" approved this decision. IUPAC pointed out that the Berkeley laboratory had already been recognized several times, in the naming of berkelium, californium, and americium, and that the acceptance of the names rutherfordium and seaborgium for elements 104 and 106 should be offset by recognizing JINR's contributions to the discovery of elements 104, 105, and 106.
Even after 1997, LBL still sometimes used the name hahnium for element 105 in their own material, doing so as recently as 2014. However, the problem was resolved in the literature as Jens Volker Kratz, editor of Radiochimica Acta, refused to accept papers not using the 1997 IUPAC nomenclature.