CMU chemist leads team to confirm four new elements

The seventh row of the periodic table of elements is now complete. The fourth Joint Working Party (JWP), a small international group of experts charged to review whether the claims satisfy the criteria to be recognized as a new element, on behalf of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), has confirmed the stable existence of elements 113, 115, 117, and 118.

An element’s atomic number is what distinguishes one element from another. Each element has its own specific atomic number, which represents the number of positively charged particles, or protons, in the nucleus. In order to verify an element’s existence and to assign it a definite atomic number, scientists use criteria established by the Transfermium Working Group, which evaluates elements with atomic numbers above 100. These criteria are essentially descriptions of possible experimental techniques and measurements.

In an interview with The Tartan, Paul Karol, chair of the JWP and Professor Emeritus of Chemistry at Carnegie Mellon, explained this process and how it influenced the approval of the new elements.

“A particular difficulty in establishing these new elements is that they decay into hitherto unknown isotopes of slightly lighter elements that also need to be unequivocally identified,” Karol said. “In the future, we hope to improve methods that can directly measure the atomic number, Z.”

Elements which are under review are identified by the atomic number (Z) that they are set to occupy. Karol explained the production of Z = 118 as a matter of simple addition; by combining Z = 20 (Calcium) with Z = 98 (Californium) through fusion, one obtains Z = 118.

“That fusion, as opposed to a scattering or many other processes, so rarely results in a viable 118 product that one must be extraordinarily careful about identifying the product in the midst of many, many similar outcomes of the nuclear collision. It is truly searching for a needle in a haystack,” Karol said.

A typical experiment, done in Russia or Japan for example, might run for a month, during which one or two candidate products get tentatively identified among a sea of uninteresting signals. Then those candidates need to be measured to look for convincing identifying signals that confirm the interpretation that the result is valid.

All those steps need to be vetted to be certain there are not alternative interpretations. Ultimately, the group follows guidelines in the criteria to see whether or not the radioactive species proceed through subsequent decay steps that match previously identified radioactivities of known elements. According to Karol, duplication of results is extremely important as well. This can take years of experimentation to achieve.

The critical review process involves a small international team of experts who immerse themselves in the experimental record to see if the criteria have been met. The team communicates entirely through the Internet and, although very enthusiastic about recognizing new discoveries, is committed to looking into every possible alternative explanation of the results.

This tenacity is necessary due to the high likelihood of false positives. Each time the JWP has been assembled to examine a discovery claim, the process has taken between two and three years. Though it is a long time, it involves very careful wording and rewording of the team’s interpretation so as not to criticize the founding researcher. They are very careful not to discourage researchers from performing challenging experiments, and the committee makes it a point to be as clear as possible with their concerns.

“Our draft recommendations are then sent to the laboratories themselves for technical review, not of our recommendation, but of the data we considered and the understanding of the chemistry and physics involved. That review takes a few months,” Karol said in an email interview with The Tartan.

“Back then to us for possible/probable revision, and then out to the International Unions for peer review, followed by the inevitable revisions and ultimately to the journal [*Pure and Applied Chemistry*] for editorial revision. All this chews through the calendar.”

As the chair of JWP, Karol said that he is always excited about new element discoveries. “They are becoming more and more difficult to achieve, yet more and more informative about what lies ahead, as far as possible surprises are concerned.”

Though there are no practical applications of these newly discovered elements in the near future, Karol proposes that “if the chemistry is explored, it will give an important handle on what are the effects of relativity on chemical behavior for these very heavy atoms since the imposition of relativistic effects on electron properties in atoms is still theoretically primitive and further known chemistry would be of enormous use.”

Further research in this field would allow committees such as Karol’s to confirm new elements with much more efficiency.