Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session C5: Nuclear Structure at the Limits of Stability |
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Sponsoring Units: DNP Chair: Dan Bardayan, Oak Ridge National Laboratory Room: Royal AB |
Saturday, April 30, 2011 1:30PM - 2:06PM |
C5.00001: Discovery of new superheavy element isotopes Invited Speaker: The first confirmation of element 114 production and decay was performed in 2009 with the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. The $^{48}$Ca~+~$^{242}$Pu reaction was used. Compound nucleus evaporation residues were separated from beam and other reaction products with the Berkeley Gas-filled separator and implanted in the focal plane detector system. Production and decay of one atom each of $^{287}$114 (via the $^{242}$Pu($^{48}$Ca,~3$n)^{287}$114 reaction) and $^{286}$114(via the $^{242}$Pu($^{48}$Ca,~4$n)^{286}$114 reaction) were observed. Production cross sections, decay modes, decay energies, and half-lives and for these element 114 isotopes and their daughters were consistent with those reported by the Dubna Gas Filled Recoil Separator Group (Yuri Oganessian$,$ J. Phys. G: Nucl. Part. Phys. \textbf{34 }(2007) R165--R242). In 2010, the $^{48}$Ca~+~$^{242}$Pu reaction was used again, at an increased beam energy to optimize the production of new isotope, $^{285}$114, by the $^{242}$Pu($^{48}$Ca,~5$n)^{285}$114 reaction. The production and decay of one atom of $^{286}$114 (via the $^{242}$Pu($^{48}$Ca,~4$n)^{286}$114 reaction) was observed, re-confirming the properties of this isotope. In addition, a single event corresponding to the production and decay of $^{285}$114 (via the $^{242}$Pu($^{48}$Ca,~5$n)^{285}$114 reaction) was observed. The implantation of $^{285}$114 in the detector was followed by five \textit{$\alpha $}-decays and a spontaneous fission event, indicating the \textit{$\alpha $}-decays of new isotopes, $^{285}$114, $^{281}$Cp, $^{277}$Ds, $^{273}$Hs, $^{269}$Sg, and the spontaneous fission of new isotope, $^{265}$Rf. The decay properties of all these new isotopes match expectations based on microscopic-macroscopic mass models supplemented with extrapolations of previously reported superheavy element isotope decay properties. However, some systematic differences between observed and predicted \textit{$\alpha $}-decay $Q$-values may be used to refine models of nuclear shell effects in heavy element isotopes. [Preview Abstract] |
Saturday, April 30, 2011 2:06PM - 2:42PM |
C5.00002: Discovery of particle unstable $^{69}$Br Invited Speaker: Two-proton capture on $^{68}$Se through $^{69}$Br provides a possible mechanism to bypass the waiting point at $^{68}$Se during explosive hydrogen burning processes on neutron stars. This two-proton capture rate, however, depends exponentially on the $^{69}$Br proton separation energy. We have determined the proton separation energy for $^{69}$Br to be -785+34-40 keV by a direct measurement of the p+$^{68}$Se decay products.\footnote{A M Rogers, W G Lynch, M A Famiano, M S Wallace, F Amorini, D Bazin, R J Charity, F Delaunay, R T de Souza, J Elson, A Gade, D Galaviz, S Hudan, J Lee, S Lobostov, S Lukyanov, M Matos, M Mocko, M B Tsang, D Shapira, L G Sobotka, G Verde, arXiv:1009.2950.}$^,$\footnote{Supported NSF Grant Nos. PHY-0216783, PHY-0606007, PHY-0822648, and PHY-0855013, and DoE Grant Nos. DE-FG02-87ER-40316 and DE-AC02-06CH11357.} This extracted value is less bound than that obtained from Coulomb displacement energy calculations and the known masses for $^{69}$Se and $^{68}$Se. The influence of our value for the proton separation energy for $^{69}$Br on rp-process occurring in Type 1 X-ray bursts is examined in a one-zone burst model. [Preview Abstract] |
Saturday, April 30, 2011 2:42PM - 3:18PM |
C5.00003: Transfer reactions with HELIOS Invited Speaker: Nucleon-transfer reactions have formed the backbone of nuclear- structure studies for several decades, providing a wealth of information about the energies, quantum numbers, and wave functions of single-particle states in nuclei throughout the nuclear chart. Current trends in nuclear-structure physics and the modern emphasis on properties of neutron-rich nuclei far from stability have renewed interest in such transfer reactions with radioactive beams. Here, the usual combination of light beam and heavy target cannot be used, and measurements must be performed in ``inverse kinematics,'' with a heavy, unstable beam incident on a light target. This arrangement introduces several technical difficulties, including the identification of the reaction products and the resolution of the states of interest in the residual nuclei. A new device, HELIOS (the HELIcal Orbit Spectrometer) at the ATLAS facility at Argonne National Laboratory, solves many of the problems encountered with inverse kinematics including particle identification and energy resolution in the center-of-mass frame. The device utilizes the uniform magnetic field of a large, superconducting solenoid to transport light reaction products from the target to a linear array of position-sensitive silicon detectors. The properties of HELIOS will be described, and examples from the initial research program that focuses on neutron transfer with the (d,p) reaction, using both stable and unstable beams with mass A=11 to 136, will be presented. [Preview Abstract] |
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