Physicists Synthesize Four New Elements

By Mary Rose Thomas-Glaser

Four of the heaviest elements ever discovered have been officially recognized by the International Union of Pure and Applied Chemistry to complete the seventh row of the periodic table. These yet-to-be-named elements, 113, 115, 117 and 118, were created in a series of experiments conducted by nuclear physicists in the United States, Russia and Japan between 2002 and 2010.

Search for Stable, Superheavy Isotopes

All elements are identified by their atomic number, or the number of protons in their nucleus. Only the elements below Uranium (92) are found naturally on Earth. All heavier elements, including the four newest, have been produced in nuclear reactors or with particle accelerators. Elements lighter than Lead (82) are “stable” and will not decay or change. Conversely, heavier, “unstable” elements lose energy by releasing radiation and decay into less radioactive and more stable elements. The time it takes for half of a radioactive element’s atoms to decay is known as its half life.

Scientists have known that the nuclei of stable elements are held together more securely. The protons and neutrons in these elements are arranged in a series of shells that provide additional stability. In the 1960s, researchers discovered that the key to added stability of natural elements is their so-called magic number of protons and neutrons.

Based on the stability of natural elements, researchers theorized that maintaining the ideal proton-neutron ratio would confer extra stability to superheavy elements. Since then, physicists have sought to prove the theoretical “island of stability” for heavier elements with nuclei containing 184 neutrons and 114 protons.

In numerous experiments using particle accelerators, researchers fired beams of lighter nuclei onto films of heavy metal. In rare instances during this beam bombardment, a nucleus was hit head on. When such a collision happened, a compound nucleus was created and projected outward where a detector captured the timing of decay and energy of decay products.

The recent experiments produced the four newest superheavy elements. Only a few atoms of each new element were created, and none survived more than a few hundred milliseconds before radioactively decaying. Nonetheless, researchers are one step closer to the elusive island of stability. While these elements lack any current practical application, they help researchers to better understand the forces that hold a nucleus together.