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ISHII Tetsuro Japan Atomic Energy Agency

In-beam g -ray spectroscopy of neutron-rich nuclei in the uranium region through the heavy-ion transfer reaction. JAEA H. Makii, M. Asai, H. Koura, K. Tsukada, A. Toyoshima, M. Matsuda, T. Shizuma, S. Ichikawa Tokyo Institute of Technology S. Shigematsu, T. Kohno

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ISHII Tetsuro Japan Atomic Energy Agency

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  1. In-beam g-ray spectroscopy of neutron-rich nuclei in the uranium region through the heavy-ion transfer reaction JAEA H. Makii, M. Asai, H. Koura, K. Tsukada, A. Toyoshima, M. Matsuda, T. Shizuma, S. Ichikawa Tokyo Institute of Technology S. Shigematsu, T. Kohno National Defense Medical Colledge A. Makishima Komazawa Univ. J. Kaneko, M. Ogawa Osaka Univ. I. Hossain, Ibaraki Univ. H. Toume ISHII Tetsuro Japan Atomic Energy Agency JAEA-Tokai Tandem Accelerator

  2. Nuclear structure at the largest neutron number Where are deformed / spherical shell gaps ? high-L (k17/2) orbitals ? ►In-beam g-ray spectroscopy using heavy-ion transfer reactions - 238U,244Pu,248Cm targets; (18O,16O), (18O, 20Ne) selection of reaction channels using Si DE-E ► First g-ray measurements of 236Th, 240,242U, 246Pu, 250Cm - establishment of ground-state bands up to 12+ states ► Systematics of E(21+) in the neutron-rich U region - disappearance of N=152 deformed shell gap at 94Pu - possibility of the spherical shell gap at N=164 for 256U164

  3. (18O,16O) 2n stripping (18O,20Ne) 2p pickup More Neutron-rich than the b-stability b-stability 294110Ds184 T1/2 ~300y

  4. Experimental setup 18O beam 162 MeV(18MV) @Tokai-Tandem 248Cm target (0.8mg/cm2) f3mm, 45kBq • 4 Si DE-E telescopes • DE: 75mm thickness 6 Ge detectors Seff = 12% @ 0.2 MeV 3% @ 1.3 MeV

  5. E-DE Plots & g-ray spectra of 250Cm154 248Cm(18O,16O)250Cm; 2neutron-stripping s~0.5mb Si E-DE PLOT F DE∝AZ2/E O N C B Be

  6. E-DE Plots & g-ray spectra of 250Cm154 248Cm(18O,16O)250Cm; 2neutron-stripping Si E-DE PLOT gate Ex of 250Cm < Sn Complete selection of g-rays in residual nuclei by measuring outgoing particles - Z, A, and kinetic energies -

  7. Level schemes of 240U, 246Pu and 250Cm by (18O,16O)

  8. Level Schemes of 236Th and 242U by (18O,20Ne)

  9. if deformed shell gap exists, pairing energy gap (D) moment of inertia (E2+) cranking model Moments of inertia and N=152 deformed shell Experiment Five new data Calculation Sobiczewski et al., PRC 63(2001)034306

  10. Narrower energy gap at N=152 for 94Pu Experiment 245Pu151 1/2[620] present in-beam g-ray data combined with the (d,p) data at ANL in ’70s 9/2[734]

  11. Possibility of spherical shell closure of N=164 in the U region 25692U164 is spherical？ N=126 Minimum pairing energy gap (D) moment of inertia (E2+) Deformed shell gap

  12. S.P.E. calculated by Koura-Yamada potential (modified Woods-Saxon)

  13. Summary • First measurements of deexcitaion g-rays in 5 neutron-rich nuclei in the U region (18O, 16O) 2n-strippping; 240U, 246Pu and 250Cm up to 12+ s~0.5mb (18O, 20Ne) 2p-pickup ; 236Th and 242U up to 10+ and 8+s~mb - complete selection of g-rays by Z and M by measuring the outgoing particles with Si DE-E 250Cm154 : first in-beam g-ray study beyond N=152 • Disappearance of N=152 deformed shell gap for 94Pu - from the systematics of the E(21+) energies and from the single particle levels in 245Pu151 • Possibility of the spherical shell closure of N=164 - supported by the calculation using the Koura-Yamada potential 240U: T. Ishii et al., Phys. Rev. C 72 (2005) 021301(R) 250Cm: T. Ishii et al., J. Phys. Soc. Jpn. 75 (2006) 043201

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