Speaker
Description
Several experiments aiming at studying the low energy parts of the Electric Dipole response (the so called Pygmy Dipole Resonance, PDR) in nuclei were carried out during the years and are presently being made. Use of different probes and techniques was made and nuclei in different mass regions were investigated.
The interest in the PDR states is related to their astrophysical implications in the nucleosynthesis and also because the underlying structure of the PDR is under active debate and scrutiny. The PDR’s isospin splitting was revealed in complementary experiments with isoscalar and isovector probes exciting states in several nuclei, suggesting that the PDR splits into a lower-energy isoscalar surface mode and a higher-energy component with an isovector admixture from IVGDR. Some possible evidence for the electric pygmy quadrupole states was also found.
More recent directions concern the search of E1 decay from states with angular momentum higher than zero and experiments detecting gamma-rays from fission products.
A difficul task is to identify pygmy states in nuclei at finite temperature and for this purpose dedicated experimental efforts are being made. Indeed, this signal is of great interest because the nucleosynthesis in the stellar environment involves nuclei which are not necessarely in the ground states.
To underline the importance of the PDR investigations selected results, open problems and future plans will be presented and discussed. Special emphasis is given to the plans with the PARIS detector arrays.