Dubnium

Dubnium is a chemical element on the periodic table of elements with the symbol Db and its atomic number 105. The element was named after the city of Dubná, Russia, home of the Central Institute for Nuclear Research, where it was first produced. It is a synthetic and radioactive element; and its most stable known isotope, dubnium-268, has a half-life of approximately twenty-eight hours.

In the periodic table of elements, it is an element of the d block and it is a transactinide element. It is a member of the seventh period and belongs to group 5 of elements. Chemical experiments confirmed that dubnium behaves like the heavier homologue of tantalum in group 5. The chemical properties of dubnium are partially known. The element is similar to others in group 5.

In the 1960s, microscopic amounts of dubnium were produced in laboratories in the Soviet Union and California. It was discovered by the Russian Georgui Fliórov in 1967-1970, and by the American Albert Ghiorso in 1970. When it was discovered, the priority of discovery, and therefore the naming of the element, was disputed between Soviet and American scientists, who Some proposed calling it Nielsbohrio and others Hahnio, although these names were not internationally recognized. Since then the element was temporarily renamed unnilpentium, until in 1997 the International Union of Pure and Applied Chemistry —IUPAC for its acronym in English — established dubnium as the official name of the element.

History

Discovery

The existence of dubnium was first indicated in 1968 by Russian scientists at the Central Institute for Nuclear Research (ICIN) in Dubna, Soviet Union (now Russia). There the researchers bombarded an americium-243 target with neon-22 ions. They reported the measurement of alpha activity emissions of 9.40 MeV and 9.70 MeV and determined that the decays came from the ²⁶⁰Db or ²⁶¹Db isotopes:

95243Am+1022Ne→ → 105265− − xDb+xn{displaystyle ,_{95}^{243}mathrm {Am} +,_{10}{22}{22}mathrm {Ne} to ,_{105}{265-x}mathrm {Db} +xmathrm {n} }

Two years later, the Dubná team separated their reaction products using thermal gradient chromatography after conversion to chlorides by interaction with NbCl₅. The team observed a spontaneous fission activity of 2.2 seconds contained in a volatile chloride possessing eka-tantalum properties, probably dubnium-261 pentachloride, ²⁶¹DbCl₅.

At the end of April 1970, a group of researchers led by Albert Ghiorso of the University of California, published the details of the synthesis of ²⁶⁰Db by bombarding a californium-249 target. with nitrogen-15 ions, and measured the alpha decay of ²⁶⁰Db with a half-life of 1.6 seconds and a decay energy of 9.10 MeV, correlated with the decay product of lawrencio-256:

95249Cf+715N→ → 105260Db+4n{displaystyle ,_{95}^{249}mathrm {Cf} +,_{7}{15}{15mathrm {N} to ,_{105}^{260}mathrm {Db} +4mathrm {n} }

These results by the Berkeley scientists did not confirm the Soviet findings regarding the 9.40 MeV or 9.70 MeV alpha decay of dubnium-260, leaving only dubnium-261 as the possibly produced isotope. In 1971, the Dubná team repeated their reaction with a better set-up and were able to confirm the decay data for ²⁶⁰Db with the reaction:

95243Am+1022Ne→ → 105260Db+5n{displaystyle ,_{95}^{243}mathrm {Am} +,_{10}{22}{22}mathrm {Ne} to ,_{105}{260}mathrm {Db} +5mathrm {n}} }

In 1976, the Dubná team continued their study of the reaction using thermal gradient chromatography, and were able to identify the product as dubnium-260 pentabromide, ²⁶⁰DbBr₅.

In 1992, the IUPAC/IUPAP Transfermium Working Group evaluated the claims of the two groups and concluded that confidence in the discovery grew from the results of both laboratories, and therefore, the discovery claim should be shared.

Naming controversy

Niels Bohr

Otto Hahn

Originally the Soviet team had proposed that item 105 be called nielsbohrio (Ns) in honor of Danish nuclear physicist Niels Bohr (in the left image). The U.S. team initially proposed that the element be named Hahnio in honor of the German chemist Otto Hahn (in the right image), known as the pioneer in the field of radioactivity and radiochemicals.

The Soviet team proposed the name nielsbohrio (Ns) after the Danish nuclear physicist Niels Bohr. The US team suggested that the new element should be named hahnium (Ha), after the German chemist Otto Hahn. Consequently, hahnium was the name that many American and Western European scientists used, appearing in many published writings at the time, and nielsbohrium was used in the Soviet Union and Eastern Bloc countries.

Thus a controversy broke out between the two groups about the name of the element. Therefore, the IUPAC adopted unnilpentium (Unp) as the systematic temporary name for element. In 1994, trying to solve the problem, the IUPAC proposed the name joliotio (Jl), in honor of the French physicist Frédéric Joliot-Curie, a name that had been proposed by the Soviet team for element 102, named later as nobelius. The two main claimants continued to disagree over the names of elements 104 to 106. However, in 1997, the dispute was resolved and the current name, dubnium (Db), was adopted in honor of the Russian city of Dubna, the location of the Central Institute for Nuclear Research. On this, the IUPAC argued that the Berkeley laboratory had already been recognized several times in the naming of the elements (for example, berkelium, californium, americium) and that the acceptance of the names rutherfordium and seaborgium for elements 104 and 106 should be offset by acknowledging the contributions of the Russian team in the discovery of elements 104, 105 and 106.

Isotopes

A nucleid stability chart used by JINR in 2012. Characterized isotopes are shown with edges.

Dubnium, which has an atomic number of 105, is a superheavy element; Like all elements with such high atomic numbers, it is highly unstable. The longest-lived isotope of dubnium, ²⁶⁸Db, has a half-life of around one day. No stable isotopes have been seen and a 2012 JINR calculation suggested that the half-lives of all dubnium isotopes would not significantly exceed one day. The current experimental value is 28+11
−4 hours for ²⁶⁸Db, but the law of large numbers statistics, in on which the determination of half-lives is based, cannot be directly applied due to a very limited number of experiments (decays). The uncertainty range is an indication that the half-life is within this range with a 95% probability. Dubnium can only be obtained through artificial production. Modern theory of the atomic nucleus does not suggest a long-lived living isotope of dubnium, but it was claimed in the past that unknown isotopes of superheavy elements existed primarily on Earth: for example, such a claim was made for ²⁶⁷ 108 of a half-life of 400 to 500 million years in 1963 or ²⁹²122 of a half-life of more than 100 million years in 2009; ⁣ neither statement gained acceptance.

Dubnium's short half-life limits experimentation. This is compounded by the fact that the most stable isotopes are the most difficult to synthesize. Elements with lower atomic number have stable isotopes with a higher neutron-proton ratio than those with higher atomic number, which means that the target and beam nuclei that could be used to create the superheavy element have fewer neutrons than are needed to form these more stable isotopes. (Different techniques based on fast neutron capture and transfer reactions are being considered as of the 2010s, but those based on the collision of a large and small nucleus still dominate research in the area.)

Only a few ²⁶⁸Db atoms can be produced in each experiment, and therefore the measured lifetimes vary significantly during the process. Over three experiments, 23 total atoms were created, with a resulting half-life of 28+11
−4 hours. The second The more stable isotope, ²⁷⁰Db, has been produced in even smaller quantities: three atoms total, with lifetimes of 33.4 h, 1.3 h, and 1.6 h. These two are the heaviest isotopes of dubnium to date, and both were produced as a result of the decay of the heavier nuclei ²⁸⁸Mc and ²⁹⁴Ts rather than directly, because the experiments that produced them were originally designed in Dubna for 48Ca beams. For its mass, ⁴⁸Ca has by far the largest neutron excess of all practically stable nuclei, both quantitative and relative, ⁣ which, consequently, helps to synthesize superheavy nuclei with more s neutrons, but this gain is offset by the lower probability of fusion for high atomic numbers.

Additional bibliography

• Audi, G.; Kondev, F. G.; Wang, M. et al. (2017). «The NUBASE2016 evaluation of nuclear properties». Chinese Physics C (in English) 41 (3): 30001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
• Beiser, A. (2003). Concepts of modern physics (in English) (6th edition). McGraw-Hill. ISBN 978-0-07-2448-1. OCLC 48965418.
• Hoffman, D.C.; Ghiorso, A.; Seaborg, G.T. (2000). The Transuranium People: The Inside Story (in English). World Scientific. ISBN 978-1-78-326244-1.
• Kragh, H. (2018). From Transuranic to Superheavy Elements: A Story of Dispute and Creation (in English). Springer. ISBN 978-319-75813-8.
• Zagrebaev, V.; Karpov, A.; Greiner, W. (2013). «Future of superheavy element research: Which nuclei could be synthesized within the next few years?». Journal of Physics: Conference Series (in English) 420 (1): 012001. Bibcode:2013JPhCS.420a2001Z. ISSN 1742-6588. S2CID 55434734. arXiv:1207.5700. doi:10.1088/1742-6596/420/1/012001.