Swedish researchers have reported strong evidence for the formation of element 115, some 9 years after Russian researchers first claimed to detect a nucleus with 115 protons.

A team led by nuclear physicist Dirk Rudolph of Lund University in Sweden formed element 115 by smashing isotopes of calcium into a film of americium at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. The scientists monitored the emissions of alpha particles and X-rays to try to fingerprint decay products.

“I am quite satisfied with the success of the experiment as such; it was not easy to get it scheduled in the first place, but then it went technically and scientifically very well, even on short notice,” says Rudolph.

Their findings are accepted for publication in Physical Review Letters. They build on results obtained at the Flerov Laboratory for Nuclear reactions in Dubna, Russia, in 2004, which suggested that a nucleus containing 115 protons had fleetingly formed. In 2011, the International Union of Pure and Applied Chemistry, which names new elements, deemed that result too tentative to be a claim of discovery, although Dubna was recognized for co-discovering elements 114 and 116.

Now, Rudolph and his colleagues say they have identified more than 30 chains of nuclear decay products that may have originated with the formation of element 115. The element is now tentatively called ununpentium, but the The International Union of Pure and Applied Chemistry (IUPAC) has yet to recognize or name it. Rudolph says in a 28 August web posting that his team expects that IUPAC may seek yet more statistically significant evidence before ruling on the new element’s existence.

Further studies of the decay products should provide new glimpses into the world of extremely heavy nuclei, some of which deviate from the naively spherical picture of the nucleus and take on other shapes, including oblate, prolate, and most recently, pear-shaped.

Update 30 August: this blog post originally stated that publication in Physical Review Letters was scheduled for 27 August. Publication has since been delayed.