Swedish researchers have conducted an experiment that confirms the existence of a new artificial element with an atomic number of 115 - temporarily named ununpentium.
The new research, carried out by a team from Sweden's Lund University and led by Prof. Dirk Rudolph, builds on the earlier work done by Russian physics groups - duplicating the creation of Element 115, as well as contributing some additional findings which may help the IUPAC international comittee decide when to officially add this new element to the periodic table.
Target wheel from the TASCA system used to create atoms of the superheavy element 115 at GSI in Germany. The areas where the films have been bombarded by calcium ions are clearly visible. Image Credit: G. Otto/GSI
The experiment was conducted in November 2012, at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt in Germany. The GSI has an incredibly strong track record for discovering elements. The lab has now hosted key experiments for the discovery of no fewer than seven artificial elements - 107 through 112, and now 115.
The experiment consisted of firing ions of a rare isotope of calcium (48Ca) at targets made of thin films of Americum (243Am) created at Oak Ridge National Lab in the USA. Occasionally (1.5 times per day on average), these two elements fused to form an isotope of element 115, with a mass number of 288. Although the element has a half-life of 140-190 milliseconds, it's presence was proven by the characteristic chain of more stable decay products it leaves behind.
Prof. Rudolph's team was able to observe 30 of these decay chains - adding to the 37 total observances reported from various Russian experiments at the Dubna facility, the first of them in 2003. The duplication of the experiment at a second location is one of the key aspects that the judging committee requires to give the element a permanent name and a permanent place in the periodic table.
The international committee is formed of members of the IUPAC and IUPAP - the International Unions of Pure and Applied Chemistry, and of Physics. This group keeps track of all the published evidence of the new element, making sure that all the regulations have been met.
The TASCA experimental setup at the GSI facility - one of the most effective instruments in the world for detecting superheavy elements. Image Credits: G. Otto/GSI
Once the element's existence is judged to have been proved, the committee will oversee the selection of a name - suggested by the discovering research group and approved by the scientific community at large. Until that point, the element will keep it's placeholder name, Ununpentium - although most scientists refer to it simply as Element 115.
In addition to the observation of the characteristic radioactive alpha-decay patterns, the Swedish team also made a secondary breakthrough. They were able to simultaneously measure x-ray photons emitted from some of the decay products.
On their own, these x-ray emissions are not enough to prove that the superheavy element was formed. However, they do provide a sort of parallel second experiment, to add to the statistical weight of the findings.
This is also a useful proof-of-concept - they have shown that this x-ray fingerprinting can be carried out with existing equipment, at the same time as an alpha decay experiment, which may prove very useful in future experiments.
Whilst there are clearly no practical materials science applications for Element 115 - due to a half-life of less than 200ms and a production rate of less than 2 atoms a day - this is a highly significant discovery in physics, and will contribute greatly to our understanding of how nuclear physics works when taken to these extreme conditions.