Element 117 and its long-lived granddaughters

Researchers in Russia and the US have collaborated to synthesize a new element with atomic number Z = 117. They’ve done it using the same technique they used over the past dozen years to make elements 113--116 and 118: bombarding an actinide target—berkelium in this case—with a beam of calcium-48 ions energetic enough to fuse with the actinide nuclei. Six atoms of element 117, five with 176 neutrons and one with 177, became lodged in position-sensitive detectors, where each underwent a series of alpha decays followed by a spontaneous fission. The timing and energy pattern of the observed decays allowed the researchers to identify new atoms. Along the alpha-decay chains were new isotopes of elements 115 and 113, roentgenium (Z = 111), meitnerium (109), bohrium (107), and dubnium (105), all with more neutrons than the previously known isotopes of those elements. The greater neutron numbers N brought with them greater stability and longer half-lives, in agreement with the theory that predicts an island of stability somewhere around Z = 114--126 and N = 184. In particular, the new isotopes of element 113 each lived for several seconds, long enough that the researchers hope to be able to probe the element’s electronic—that is, chemical—properties. With electrons moving at relativistic speeds, element 113 might not behave at all like thallium, the element just above it in the periodic table. (Y. T. Oganessian et al., Phys. Rev. Lett. 104, 142502, 2010 .)—Johanna Miller

PACS: 27.90.+b, 23.60.+e, 25.70.Jj, 24.60.Dr