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Microscopic description of the fission process Witold Nazarewicz NNSA Extreme Computing Workshop October 6-8, 2009

Microscopic description of the fission process Witold Nazarewicz NNSA Extreme Computing Workshop October 6-8, 2009. Powerful phenomenology exists… … but no satisfactory microscopic understanding of: Barriers Fission half-lives Fission dynamics Cross sections … What is needed?

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Microscopic description of the fission process Witold Nazarewicz NNSA Extreme Computing Workshop October 6-8, 2009

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  1. Microscopic description of the fission process Witold Nazarewicz NNSA Extreme Computing Workshop October 6-8, 2009

  2. Powerful phenomenology exists… • … but no satisfactory microscopic understanding of: • Barriers • Fission half-lives • Fission dynamics • Cross sections • … • What is needed? • Effective interaction • Microscopic many-body techniques • Algorithms • Hardware

  3. http://www.phys.utk.edu/witek/fission/fission.html

  4. V(q) E q Adiabatic Approaches to Fission WKB: collective inertia (mass parameter) multidimensional space of collective parameters The action has to be minimized by, e.g., the dynamic programming method. It consists of calculating actions along short segments between adjacent, regularly spaced hyperplanes, perpendicular to the q-direction [A. Baran et al., Nucl. Phys. A361, 83 (1981)]

  5. b a The shortest path determined by dynamic programming method. The grid points represent the mesh in a 2D space {x} in which the functional S[x(s)] is defined. Thick zig-zag line represents the shortest path (S=0) starting from the point (a) and ending at the final point (b). A. Baran et al., Nucl. Phys. A361, 83 (1981)

  6. Collective inertia B(q) and ZPE Various prescriptions for collective inertia and ZPE exist: GOA of the GCMRing and P. Schuck, The Nuclear Many-Body Problem, 1980 ATDHF+Cranking Giannoni and Quentin, Phys. Rev. C21, 2060 (1980); Warda et al., Phys. Rev. C66, 014310 (2002) Goutte et al., Phys. Rev. C71, 024316 (2005) A.Baran et al., nucl-th/0610092 HFODD+BCS+Skyrme Recently, a nice progress with full ATDHFB inertia….

  7. Microscopic description of complex nuclear decay: Multimodal fission • Staszczak, A.Baran, J. Dobaczewski, W.N., Phys. Rev. C 80, 014309 (2009)

  8. Fission: isothermal or isentropic, or …? M. Diebel, K. Albrecht, and R.W. Hasse, Nucl. Phys. A 355, 66 (1981) M.E. Faber, M. Ploszajczak, and K. Junker, Acta Phys. Pol. B 15, 94 (1984) Numerical test

  9. Particle gas component Can be removed Its magnitude is related to particle width P. Bonche, S. Levit, and D. Vautherin, Nucl. Phys. A 427, 278 (1984); 436, 265 (1985)

  10. Systematic Study of Fission Barriers of Excited Superheavy Nuclei • Sheikh, WN, Pei, Phys. Rev. 80, 011302(R) (2009) • Focus on: • Mirror asymmetry and triaxiality at high temperatures • Systematic analysis of barrier damping

  11. Research goals, mid-term (1) • Applications of modern adiabatic and time-dependent theories • Use modern NEDF optimized for deformation effects • Perform action minimization on many-dimensional meshes • Develop symmetry restoration schemes for DFT • Increase the number of collective coordinates in GCM, including pairing channel • Develop time-dependent framework for fission from excited states (T>0): ATDHFB and TDHFB J. Skalski: Phys. Rev. C 77, 064610 (2008) Nuclear fission with mean-field instantons ATDHFB inertia

  12. Research goals, mid-term (2) • Tests of non-adiabatic approaches • Non adiabatic tunneling, properly accounts for level crossings and symmetry breaking effects (collective path strongly influenced by level crossings). ATDHF not adequate • Evolution in an imaginary time • The lifetime is expressed by the sum of bounces • Difficulty in solving the periodic mean-field equations (fission bounce equations) • Important role of pairing correlations (restore adiabaticity) • Unclear how to restore broken symmetries bounce trajectory governing fission

  13. SUMMARY • Fission is a perfect problem for the extreme scale • Quantum many-body tunneling is tough • Broken symmetries imply that many dimensions are involved • Adiabatic picture should work well for spontaneous fission. Here the main challenge is multidimensional optimization of action. Interference between various fission pathways can play a role • For excited-state fission adiabatic picture questionable. TDHFB is an option for high excitations. • Imaginary time approach seems to be the tool of choice. However, bounce trajectories are difficult to determine.

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