Dubnium · element 105
Two superpowers argued over this element for almost thirty years before a Russian town won the name
Key facts
Dubnium sits directly below tantalum in group 5, and for most of its history it did not have an agreed name. Soviet scientists called it nielsbohrium. American scientists called it hahnium. Textbooks printed one or the other depending on which side of the Iron Curtain they were published, and the argument was not settled until 1997.
The name that finally stuck honours Dubna, a small town on the Volga north of Moscow that is home to the Joint Institute for Nuclear Research. It is one of only a handful of elements named after the place where it was made, alongside berkelium, darmstadtium and livermorium.
Where it is found
Dubnium does not exist anywhere on Earth or, as far as anyone knows, anywhere in nature. Every atom that has ever existed was made deliberately in a particle accelerator. The total is small: across more than fifty years of experiments, scientists have probably detected only a few thousand atoms, never more than a handful at a time, and most decayed within minutes.
To make it, a beam of light nuclei is fired at a heavy target so that the two fuse. Early experiments struck americium-243 with neon-22, or californium-249 with nitrogen-15. Today the longest-lived isotope, dubnium-268, is not made directly at all. It appears at the end of a chain of alpha decays that starts with moscovium, element 115, which is itself made by firing calcium-48 at americium.
How it was discovered
The first claim came from Dubna in 1968, when Georgy Flerov's team reported alpha decays they attributed to element 105. Two years later Albert Ghiorso's group at Berkeley reported a clearer result and proposed hahnium, after the German chemist Otto Hahn. The Soviets countered with nielsbohrium, after Niels Bohr. Neither side would accept the other's evidence, and the row became part of what historians call the Transfermium Wars.
In 1992 a joint working group of IUPAC and IUPAP ruled that credit should be shared between the two laboratories. IUPAC briefly recommended the name joliotium in 1994, after the French physicist Frederic Joliot-Curie, before settling on dubnium in 1997 as a way of recognising the Russian laboratory's contribution. Hahnium never received official approval, although you may still find it in older books.
What we use it for
There is nothing you can build with dubnium. Its most stable known isotope, dubnium-268, survives for roughly a day, and only a few atoms at a time are ever available. So why keep making it?
Chemists want to know whether the periodic table still works this far down. The inner electrons of a dubnium atom move so fast that relativity changes how the outer electrons behave, which can make an element act differently from those above it. Comparing dubnium with niobium and tantalum tests that idea directly. Physicists use it as a stepping stone: because dubnium-268 turns up at the end of moscovium decay chains, identifying it helped prove that moscovium and nihonium were real.
Reading the numbers
Almost everything on this page is a prediction. The atomic mass of 268 is simply the most stable isotope known, because there is no natural dubnium to average. The predicted density of about 29 grams per cubic centimetre would make dubnium heavier than any metal you can hold, but nobody has ever seen a solid piece of it. No melting point, boiling point or electronegativity has been measured, which is why those boxes are blank.
The predicted electron configuration, [Rn] 5f14 6d3 7s2, gives dubnium five outer electrons and points to a +5 oxidation state, exactly like niobium and tantalum. Experiments broadly agree, but with surprises. Gas-phase tests in the late 1980s found that dubnium chloride was less volatile than a simple extrapolation predicted, and in solution dubnium has sometimes behaved more like protactinium than tantalum. It follows the group 5 pattern, but not slavishly.
Safety and the environment
Dubnium is intensely radioactive, but you will never encounter it. It is made a few atoms at a time inside shielded accelerator halls, and even its longest-lived isotope decays within days. There is no dubnium in the environment, no dubnium waste, and no route by which the public could ever be exposed.
Did you know?
- Dubnium-268 has a half-life of roughly a day, which is long enough for chemists to dissolve it and study it in solution, a rare luxury among superheavy elements.
- The unofficial name hahnium appeared in American textbooks for over twenty years, was then proposed for element 108 instead, and was finally dropped altogether.
- In 1997 IUPAC settled the disputed names of elements 104 to 109 in a single decision, ending the so-called Transfermium Wars.
- Dubnium's most stable isotope is never made directly. It appears only after moscovium, element 115, has thrown off five alpha particles in a row.
- Dubna was a closed scientific town in the Soviet era. Today it is one of the few places on the periodic table you can visit by train from Moscow.
More in the superheavy elements
The nearest neighbours of dubnium in the family, by atomic number.
See all 15 superheavy elements on one page, or browse all 118 elements. Also listed under the transition metals.
Frequently asked questions
Who is dubnium named after?
Nobody. Dubnium is named after Dubna, the Russian town north of Moscow where the Joint Institute for Nuclear Research is based. The name was chosen in 1997 to recognise the laboratory's role in discovering the element.
Why was dubnium once called hahnium?
American scientists at Berkeley proposed hahnium in 1970 in honour of Otto Hahn, who co-discovered nuclear fission. The name was widely used in the West but never officially approved, and IUPAC chose dubnium in 1997 instead.
What is dubnium used for?
Nothing practical. Only a few atoms exist at any time and they decay within hours or less. Scientists make it to test how the periodic table behaves at its extremes and to identify heavier elements whose decay chains end in dubnium.
Is dubnium dangerous?
In principle it is highly radioactive, but in practice there is none to be exposed to. It is produced a few atoms at a time in shielded laboratories and decays away within days, so it poses no risk to the public or the environment.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Dubnium reference article. Spotted an error? Tell us.