Structure of the Pygmy Dipole Resonance
Final Report Abstract
The project focused on the study of electric dipole (E1) excitations in atomic nuclei. This topic has implications not only for nuclear structure but for more fundamental questions on the symmetry of atomic nuclei and reactions in nucleosynthesis networks as well. During the project period we improved the sensitivity of the experimental setup “SONIC@HORUS” for the coincident detection of particles and γ rays at the University of Cologne by more than a factor four. In addition, the installation of ∆E-E particle telescopes allows for an identification of different scattered particles. The design and commissioning has been published. This setup was used for eight experimental campaigns where we either investigated the (p,p’γ) scattering reaction or the (d,pγ) particle transfer reaction. A wealth of information about E1 modes and their decay could be extracted and has been partly published. The comparison to data from complementary probes looks very interesting and triggered a lot of discussions in the scientific community. However, a comprehensive explanation is still missing. In addition, very successful photon scattering (γ,γ’) experimental campaigns have been performed at DHIPS (TU Darmstadt), γELBE (HZDR Dresden) and HIγS (TUNL@Duke University, NC, USA). Photons are a sensitive and model independent probe to extract the dipole response of atomic nuclei. The experiments on light nuclei show surprising M1 and E1 excitation patterns. The results have partly been published together with shell model calculations. Due to the very high level density the experiments on the heavier nuclei needed new data evaluation tools. We were one of the research groups actively involved in the international CAGRA+GRAND RAIDEN campaign at RCNP Osaka, Japan to investigate alpha and proton scattering at energies around 80-140 MeV to get information about the isospin character of E1 modes. The data analysis of these experiments is still ongoing, first results look very promising.
Publications
- “Decay of quadrupole-octupole 1− states in 40Ca and 140Ce”, Phys. Rev. C 93 (2016) 034311
V. Derya, N. Tsoneva, T. Aumann, M. Bhike, J. Endres, M. Gooden, A. Hennig, J. Isaak, H. Lenske, B. Löher, N. Pietralla, D. Savran, W. Tornow, V. Werner, and A. Zilges
(See online at https://doi.org/10.1103/PhysRevC.93.034311) - “The decay pattern of the Pygmy Dipole Resonance of 140Ce”, Phys. Lett. B 756 (2016) 72
B. Löher, D. Savran, T. Aumann, J. Beller, M. Bhike, N. Cooper, V. Derya, M. Duchêne, J. Endres, A. Hennig, P. Humby, J. Isaak, J. H. Kelley, M. Knörzer, N. Pietralla, V. Yu. Ponomarev, C. Romig, M. Scheck, H. Scheit, J. Silva, A. P. Tonchev, W. Tornow, F. Wamers, H. Weller, V. Werner, and A. Zilges
(See online at https://doi.org/10.1016/j.physletb.2016.02.042) - “The pygmy quadrupole resonance and neutron-skin modes in 124Sn”, Phys. Lett. B 752 (2016) 102
M. Spieker, N. Tsoneva, V. Derya, J. Endres, D. Savran, M.N. Harakeh, S. Harissopulos, R.-D. Herzberg, A. Lagoyannis, H. Lenske, N. Pietralla, L. Popescu, M. Scheck, F. Schlüter, K. Sonnabend, V.I. Stoica, H.J. Wörtche, and A. Zilges
(See online at https://doi.org/10.1016/j.physletb.2015.11.004) - “Combining γ-ray and particle spectroscopy with SONIC@HORUS”, Nucl. Inst. Meth. Phys. Res. A 875 (2017) 104
S.G. Pickstone, M. Weinert, M. Färber, F. Heim, E. Hoemann, J. Mayer, M. Müscher, S. Prill, P. Scholz, M. Spieker, V. Vielmetter, J. Wilhelmy, and A. Zilges
(See online at https://doi.org/10.1016/j.nima.2017.09.016) - “Investigation of J=1 states and their γ decay behavior in 52Cr”, Phys. Rev. C 98 (2018) 034315
J. Wilhelmy, B.A. Brown, P. Erbacher, U. Gayer, J. Isaak, Krishichayan, B. Löher, M. Müscher, H. Pai, N. Pietralla, P. Ries, D. Savran, P. Scholz, M. Spieker, W. Tornow, V. Werner, and A. Zilges
(See online at https://doi.org/10.1103/PhysRevC.98.034315) - “Multi-messenger investigation of the Pygmy Dipole Resonance in 140Ce”, Phys. Lett. B 786 (2018) 16
D. Savran, V. Derya, S. Bagchi, J. Endres, M.N. Harakeh, J. Isaak, N. Kalanter-Nayestanaki, E.G.Lanza, B. Löher, A. Najafi, S. Pascu, S.G. Pickstone, N. Pietralla, V.Yu. Ponomarev, C. Rigollet, C. Romig, M. Spieker, A. Vitturi, and A. Zilges
(See online at https://doi.org/10.1016/j.physletb.2018.09.025)
