Element 114 verified

In the 10 years since researchers at the Joint Institute for Nuclear Research in Dubna, Russia, first reported producing the superheavy element 114 (see Physics Today, April 1999, page 21), some tens of other sightings of the element (as well as elements 115, 116, and 118) have been documented—but all by the same group. Now a team at Lawrence Berkeley National Laboratory, led by Heino Nitsche and Ken Gregorich, has confirmed the results. Such independent verification is important, particularly given evidence of fabricated results for other superheavy elements (see Physics Today, September 2002, page 15), but it is complicated by experimental challenges, including picobarn (10⁻⁴⁰ m²) reaction cross sections and radioactive targets. Working with the lab's 88-inch cyclotron, the Berkeley team followed a process similar to that used at Dubna: They aimed an accelerated beam of calcium-48 ions at a target containing plutonium-242. The reaction products passed through a gas-filled mass spectrometer, which separated out the nuclei of interest, to a detector that yielded energy and timing information not only for the products but also for any alpha particles or fission fragments they emitted. Amid the data the researchers collected over their eight days of running the experiment, they found two correlated chains of decays that they identified as starting with ²⁸⁶114 and ²⁸⁷114. Although the lifetimes (tenths of seconds), decay modes, and decay energies agree with the Dubna results, the cross sections measured by the Berkeley team are lower. That discrepancy, say the researchers, could be due to statistical fluctuations or to some of the element-114 nuclei overshooting the detector. (L. Stavsetra et al., Phys. Rev. Lett. 103, 132502, 2009.)—Richard J. Fitzgerald