NUCL 7 |
| The existence of transactinides is determined by the structure of the heaviest nuclei. Nuclear stability increases in the vicinity of closed proton and neutron shells. The nuclear shell model predicts stability islands in the domain of superheavy elements. Enhanced stability is expected for deformed nuclei near Z=108 and N=162, yet stronger effects are predicted for spherical nuclei close to Z=114 and N=184. This lecture is devoted to experimental verification of these predictions. Fusion reactions of 208Pb, 209Bi with 50Ti, 54Cr, 70Zn, etc. projectiles (cold fusion) produce nuclides with Z=104-113, N=151-165 in the region of deformed shells (Z=108, N=162). These nuclides undergo sequential alpha-decays to known transactinides. The synthesis of heavier, neutron-rich nuclei is carried out in reactions of 233,238U, 237Np, 242,244Pu, 245,248Cm and 249Cf with 48Ca projectiles (hot fusion), creating nuclides with Z=104-118 and N=161-177. These experiments show that adding six neutrons to isotopes with Z=110-114 results in an increased stability (about five orders of magnitude) as an effect of the spherical shell N=184. The nuclides undergo sequential alpha-decays ending in spontaneous fission of long-lived isotopes of Rf and Db. Energies and half-lives have been measured for 34 nuclei and are compared with theoretical calculations from various models. This lecture presents experiments on the detection of superheavy nuclides with in-flight recoil separators. Off-line liquid phase extraction of 268Db, the final product in the decay of (288)115, and the study of elements 112 and 114 by absorption gas chromatography will be discussed. The search for superheavy elements in nature and cosmic rays, as well as the search for spontaneous fission of Hs (Z=108) and its daughters under way underground in Modane (France), will be described. Results are from FLNR (Dubna, Russia) in collaboration with LLNL (Livermore, USA) and PSI (Villigen, Switzerland), GSI (Darmstadt, Germany), RIKEN (Wako-shi, Japan) and LBNL (Berkeley, USA). |
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Developments in Advanced Characterization Techniques in Actinide and Transactinide Science
8:30 AM-12:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 253, Oral
Division of Nuclear Chemistry & Technology |