Conférences et séminaires » Séminaire présenté par le Dr F.P. HESSBERGER
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Nuclear Structure Investigations in the Region of Superheavy Nuclei .
Dr F.P. HESSBERGER
(GSI – DARMSTADT)
le Jeudi 14 juin 2007 à 16 h00
Salle de Visioconférences - Bâtiment 25
IPHC, 23 rue du Loess, Strasbourg-Cronenbourg
Even almost forty years after the first prediction of the next closed proton and neutron shells beyond the doubly magic nucleus 208Pb at Z=114 and N=184 their actual location and experimental verification is still a challenge.
Besides producing nuclei in the considered regions of Z and N and to measure some gross decay properties detailed nuclear structure investigation of heaviest nuclei is an essential tool to test the nuclear shell model at the upper border of the charts of nuclei. Thanks to improved detection systems and enhanced beam intensities such studies became possible at several laboratories during the past years for nuclei in the region .
At SHIP, GSI Darmstadt, investigations concentrated on decay studies performed in the focal plane after in-flight separation of the evaporation residues (ER) from the primary beam. Our experimental technique to establish ER - γ and α - γ correlations by means of prompt or delayed coincidence measurements allowed to study the decay of short living isomeric states in ER and levels in (daughter) nuclei populated by α-decay. As single particle levels in odd mass nuclei are essentially determined by the unpaired nucleon systematic trends are evident along the isotone’s lines in even-Z nuclei and along the isotope lines in odd-Z nuclei. Under this consideration we performed detailed decay measurements of odd-mass mendelevium isotopes 247-253Md to establish the trend of the 7/2-  Nilsson level in the einsteinium daughter isotopes. A strong correlation to the ground state deformation was observed for this particular case. Vice versa, systematic trends in single particle levels were studied in even-Z nuclei (e.g. 247,251Fm, 251,253No) along the N=145, 147, 149 and 151 – isotone’s lines up to Z=102. Isomeric states are of particular interest since they deliver (besides in-beams studies) information on levels above 0.5 MeV, which are populated only weakly by α-decay. In the course of our experiments isomeric states in 251-254No at excitation energies E* > 900 keV were either observed for the first time or confirmed. Recent experimental results are reported and tentative level assignments of the isomeric states are discussed. Personnes a contacter :