Nuclear electro-magnetic dipole modes: Skyrme-RPA predictions on flow patternand estimate of experimental accessibility

• Applicant: Professor Dr. Paul-Gerhard Reinhard
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 246273472

• Final Report Year: 2015

Final Report Abstract

On the basis of a self-consistent description of nuclear excitation spectra, we have investigated in detail the structure of a variety of excitation modes. The major part of the investigations was concerned with low lying dipole modes. We worked out that these modes are closely connected with dipole modes of toroidal and isoscalar compressional nature. In deformed nuclei, toroidal and compressional mode show remarked deformation splitting, interestingly enough in opposite order for the both modes. The search for manageable experimental signatures of toroidal strength has not yet been successful. The isoscalar monopole giant resonance poses still a puzzle: one cannot have simultaneously a pertinent description of data for heavy nuclei as 208 Pb and midshell Sn isotopes. As one may have doubts on the reliability of separable RPA, we have developed a fully fledged quasi-particle RPA (QRPA) code. But even with a now detailed treatment of low-energy pairing modes, the discrepancy for the monopole resonances persists. The next step is to scrutinize the Skyrme and pairing functional for possible solutions. New data from recent experiments on (deformed) Nd isotopes having high spectral resolution motivated an investigation of the fine structure of giant dipole and quadrupole resonances. To this end, we started to use wavelet analysis to handle the rich information hidden in data and calculations. Magnetic modes have been studied in close collaboration with experimental groups helping to analyze recent data on 50 Cr. The low-lying 1+ state found there could be identified as isovector rotational oscillations against a more or less fixed surface. A larger survey was done for low-lying γ-vibrational modes in rare-earth and actinide nuclei using QRPA. The results turned out to be very sensitive to the Skyrme force. A satisfying description for nearly considered nuclei could be obtained with a rather recent Skyrme force together with accounting approximately for a blocking effect from the quasi-particle excitations in the QRPA basis. The latter is presently an ad hoc solution for fine-tuning the results. It calls for further formal and practical analysis.

Publications

• ”Toroidal, compression, and vortical dipole strengths in 124 Sn”, Phys. Scr. T154, 014019 (2013)
  J. Kvasil, V.O. Nesterenko, A. Repko, W. Kleinig, P.-G. Reinhard, and N. Lo Iudice
  
• ”Toroidal, compression, and vortical dipole strengths in 144−154 Sm: Skyrme-RPA exploration of deformation effect”, Eur. Phys. J. A49, 119 (2013)
  J. Kvasil, V.O. Nesterenko, W. Kleinig, D. Bozik, P.-G. Reinhard, and N. Lo Iudice
  
• ”Deformation effects in toroidal and compression dipole excitations of 170 Yb: Skyrme-RPA analysis”, Phys. Scr., 89, 054023 (2014)
  J. Kvasil, V.O. Nesterenko, W. Kleinig, and P.-G. Reinhard
  
• ”Nuclear vorticity in isoscalar E1 modes: Skyrme-RPA analysis”, Phys. Rev. C89, 024321 (2014)
  P.-G. Reinhard, V.O. Nesterenko, A. Repko, and J. Kvasil
  
• ”Deformation effects in Giant Monopole Resonance”, Journal of Physics: Conference Series, 580, 012053 (2015)
  J. Kvasil, V.O. Nesterenko, A. Repko, D. Bozik, W. Kleinig and P.-G. Reinhard
  
• ”Relation of E1 pygmy and toroidal resonances”, EPJ Web of Conferences, 93, 01020 (2015)
  V.O. Nesterenko, A. Repko, P.-G. Reinhard, and J. Kvasil