The particle spectrometer SONIC for particle-γ coincidence measurements was commissioned at the Institute for Nuclear Physics in Cologne, Germany. SONIC consists of up to 12 silicon ∆E-E telescopes with a total solid angle coverage of 9 %, and will complement HORUS, a γ-ray spectrometer with 14 HPGe detectors. The combined setup SONIC@HORUS is used to investigate the γ-decay behaviour of low-spin states up to the neutron separation threshold excited by light-ion inelastic scattering and transfer reactions using beams provided by a 10 MV FN Tandem accelerator. The particle-γ coincidence method will be presented using data from a 92 Mo(p,p'γ) experiment. In a 119 Sn(d,X) experiment, excellent particle identification has been achieved because of the good energy resolution of the silicon detectors of approximately 20 keV. Due to the non-negligible momentum transfer in the reaction, a Doppler correction of the detected γ-ray energy has to be performed, using the additional information from measuring the ejectile energy and direction. The high sensitivity of the setup is demonstrated by the results from a 94 Mo(p,p'γ) experiment, where small γ-decay branching ratios have been deduced.

No abstract

Background: In the A ≈ 50 mass region M1 spin-flip transitions are prominent around 9 MeV. An accumulation of 1 − states between 5 and 8 MeV generating additional E1 strength, also denoted as Pygmy Dipole Resonance (PDR), has been established in many nuclei with neutron excess within the last decade. Purpose: The γ-decay behavior of J = 1 states has been investigated in an NRF experiment. M1 excitations have been compared to shell model calculations. Methods: J = 1 states were excited by quasi-monoenergetic, linearly polarized γ-ray beams generated by Laser-Compton backscattering at the HIγS facility, Durham, NC, USA. Depopulating γ-rays were detected with the multi-detector array γ 3 . Results: For eleven beam-energy settings the γ-decay behavior of dipole states was analyzed by a state-to-state analysis and average γ-decay branching ratios have been investigated. 34 parity quantum numbers were assigned to J = 1 states. Conclusions: Six 1 − states and two 1 + states have been investigated in NRF experiments for the first time. The M1 strength distribution is in good agreement with shell-model calculations.

No abstract

On August 17, 2017 the LIGO-Virgo Collaboration detected, for the first time, gravitational waves from the binary merger of two neutron stars (GW170817). Unlike the merger of two black holes, the associated electromagnetic radiation was also detected by a host of telescopes operating over a wide range of frequencies -opening a brand new era of multimessenger astronomy. This historical detection is providing fundamental new insights into the astrophysical site for the r-process and on the nature of dense matter. In this contribution, we examine the impact of GW170817 on the equation of state of neutron rich matter, particularly on the density dependence of the symmetry energy. Limits on the tidal polarizability extracted from GW170817 seem to suggest that the symmetry energy is soft, thereby excluding models that predict overly large stellar radii.

No abstract

The dipole response of the proton-magic nucleus $${}^{124}\hbox {Sn}$$ 124 Sn was previously investigated with electromagnetic and hadronic probes. Different responses were observed revealing the so-called isospin splitting of the Pygmy Dipole Resonance (PDR). Here we present the results of a new study of $${}^{124}\hbox {Sn}$$ 124 Sn using inelastic proton scattering at low energies to test an additional probe possibly exciting states of the PDR. The response to the new probe as well as the $$\gamma $$ γ -decay behavior of excited states were studied. The $${}^{124}\hbox {Sn}$$ 124 Sn (p,p’$$\gamma $$ γ ) experiment was performed at $$E_p = {15}\,\,\hbox {MeV}$$ E p = 15 MeV using the combined spectroscopy setup SONIC@HORUS at the Tandem accelerator of the University of Cologne. Proton-$$\gamma $$ γ coincidences were recorded, enabling a state-to-state analysis due to the excellent energy resolution for both particles and $$\gamma $$ γ rays. $$ J=1 $$ J = 1 states in the PDR region were populated in the present inelastic proton scattering experiment. Many $$\gamma $$ γ -decay branching ratios could be determined.

The Pygmy Dipole Resonance (PDR) is the dominating electric dipole excitation below and around the particle separation threshold and exhausts only a few percent of the energy-weighted sum rule. Nevertheless, it may have some impact on reaction rates in nucleosynthesis processes. Therefore, investigations to get more insights in this excitation mode are crucial. A common approach to study the PDR of atomic nuclei is the Nuclear Resonance Fluorescence method (NRF) which bases on real-photon scattering. Absolute cross sections, spin and parity quantum numbers are determined in a model-independent way if suited experimental setups are used. In general, there are two complementary NRF experiments which are presented in this paper.