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shell correction at the saddle point for mass ~ 200

shell correction at the saddle point for mass ~ 200. Kripamay Mahata GSI, Germany on leave from Nuclear Physics Division Bhabha Atomic Research Centre Mumbai, INDIA. B f. Potential Energy. Deformation. GS. Saddle. Sci. ssion. Nuclear fission. Liquid Drop Model.

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shell correction at the saddle point for mass ~ 200

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  1. shell correction at the saddle point for mass ~ 200 Kripamay Mahata GSI, Germany on leave from Nuclear Physics Division Bhabha Atomic Research Centre Mumbai, INDIA

  2. Bf Potential Energy Deformation GS Saddle Sci ssion Nuclear fission Liquid Drop Model

  3. Shell correction in fission of actinide nuclei • Asymmetric mass distn. n + 235U  144Ba + 89Kr + 3n • Fission isomer • Strutisnky shell correction method

  4. g.s Shell correction in mass ~ 200 Shell correction in mass r ~ e(aU) Shell correction in level density

  5. Earlier results from fission barrier measurement Bf = BfLD + Dn + Df RIPL-2, IAEA Moretto et. al., Phys. Rev. Lett 75, 4186 (1995) Only first chance fission

  6. Statistical Model for the decay of the compound nucleus • All possibilities are equally likely • Governed by level density (r) and Transmission coefficient (Tℓ) n fission E* Deformation

  7. Sensitivity of Cross-section, pre, A toSM Parameters • 4 sets of Bf ( = kf x BfRFRM) and af/an predict nearly same ER and fission cross-sectioons. • Pre-fission neutron multiplicity, fission anisotropy and the chance distribution of fission are very different K. Mahata et al. Nucl. Phys. A720 (2003) 209

  8. Experimental Details 19F + 188, 192Os 19F + 194, 198Pt Z2/A ~ 34 Large shell corrections near N = 126 Energies around the Coulomb barrier Evaporation residue cross-sections fission fragment angular distributions

  9. Fission Measurement DE E T1 M2 Scattering chamber setup DE E

  10. Target & Catcher F.C. Beam Evaporation Residue Measurement Off-beam intensities of charac- teristic g-lines from b decay of ER and half-life were measured Off beam g-ray counting setup

  11. Statistical model analysis Fission barrier & level density E* Un Bf = BfRFRM - Dn + Df an = ãn [1 + (Dn/Un) f(Un)] af = ãf [1 + (Df/Uf) f(Uf)] ãn = A/9, JCNdistribution from fusion Excitation function Parameter varied k= Df/Dn ãf/ãn Uf f BLD Energy Liquid drop Shell corrected Bf n Deformation

  12. Results Best fit ãf/ãn= 1.00 f/n = 0.81 Bf(0) = 11.7MeV f/n, ãf/ãn Bf ~ 20 MeV Moretto et. al., Phys. Rev. Lett 75, 4186 (1995) 35 40 45 50 55

  13. Results K. Mahata, S. Kailas and S. S. Kapoor, accepted as Rapid Comm., PRC (sept 2006)

  14. Summary & conclusion • Fission fragment angular distribution along with fission and ER excitation functions were measured in 19F + 194,198Pt, 188,192Os • Detailed statistical model analysis • Strong shell correction at the saddle deformation • Smaller fission barrier • These results will provide a useful constraint for different models, which are used to predict the fission barriers and the nuclear shapes at the extremes of charge, spin and isospin.

  15. Acknowledgement S. Kailas, and S. S. Kapoor Thank you for your kind attention

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