Brussels, 31 Jan 2006
A consortium of researchers from Switzerland, the US and Russia has succeeded in proving the existence of two new artificial elements at the famous Russian Nuclear Research Centre (JNIR) in Dubna, Russia. The as yet unnamed elements have atomic numbers 115 and 113, and are the 20th and 21st new elements to be discovered since plutonium in 1940.
Dr Heinz Gäggeler from the Paul Scherrer Institute (PSI) in Switzerland led the Swiss team, which was vital to proving the existence of the new elements. The elements had been observed before, but their existence had not yet been proved.
Dr Gäggeler spoke to CORDIS news: 'The discovery was special because it meant new elemental discoveries. In this new experiment, we have produced element 115, which does not decay to a known element, but decays by alpha radiation to an isotope unknown. We believed that the 115 element would decay to 113, which would decay to 111, to 109 to 107 and finally to 105. Our problem was to prove this.'
The experiment involved bombarding a spinning disc of Americum 243 (americum's atomic number is 95) atoms with a stream of Calcium 48 (calcium's atomic number is 20) ions inside a particle accelerator. 'Calcium 48 is a very exotic material. It is worth thousands of euros per milligram, and we required several grams to complete our experiment,' commented Dr Gäggeler.
The team hoped that the nuclei would fuse, to produce a new element - number 115. If this indeed happened, the atoms of element 115 discovered would be caught by a copper disc located behind the americum disc.
Many of the heavy, artificial elements are extremely unstable, and tend to decay by alpha-radiation. Alpha-radiation comprises two neutrons and two protons, bound together in a single package. This type of radiation is easily detected, and is key to the proof the team needed to make.
Assuming the team's theory is correct, the 115 element would decay by alpha radiation to 113, and then decay by alpha radiation again and again very rapidly until it reached element 105, which is relatively stable.
The problem for the team was testing for the 115 element as it exists for only a fraction of a second, and the same is true for all the elements down to 105, which itself exists for several hours.
This is where Dr Gäggeler's expertise came in, allowing the team to easily test for element 105: 'We did this by means of a chemical trick. Our expertise was in detecting element 105, known as Dubnium. We knew 105 chemically, through work on a different 105 isotope, and we had made our chemical preparation perfectly.'
'We went out to discover a new element, and we anticipated the result, but we were not certain,' said Dr Gäggeler. 'The result was that we found 15 atoms of dubmium - a very small amount.'
However small the quantity of dubnium, this was sufficient proof for the team. By counting the number of alpha-particles emitted, the team could work backwards from the dubnuim to arrive at elements 115 and 113. By coincidence, dubnium is named after the Russian city of Dubna where this research was carried out.
Unfortunately, although the existence of these two new elements has been proved, they are not yet eligible for names. The International Union of Pure and Applied Chemistry and International Union of Pure and Applied Physics award the names. 'Their task is to define when a new element has been identified, and then replicated. This could take five to ten years for [...] Japan, Europe or America to replicate our results. They are the only countries with suitable accelerators,' said Dr Gäggeler. 'We are convinced our results are correct, so it is just a matter of time.'
When the experiment is replicated, the team will have the privilege of naming the new elements.