[en] The experimental and theoretical evidence for the presence of octupole vibrational states in ¹⁴⁶Sm and ¹⁵⁰Nd is presented. The first nucleus which is located only two neutrons and two protons away from the N=82 shell and Z=64 subshell closures has been investigated by means of the ¹⁴³Nd(α,n) and ¹⁴⁴Nd(α,2n) fusion-evaporation reactions. The structure of the possible candidates for a 2⁺ x 3^- quadrupole-octupole multiplet are discussed in terms of the harmonic vibrational model and interpreted in terms of the Interacting Boson Approximation in the spdf boson space (IBA-spdf). The latter nucleus which is a quadrupole deformed nucleus was investigated via inelastic proton scattering which is an excellent method to excite natural parity states. Using this method, B(E1) ratios of the decaying transitions for the octupole vibrational states were determined and compared to the Alaga rule and with the IBA-spdf model. A general good agreement was found between experimental data and theoretical calculations.

[en] To gain additional information on nuclear structure from particle-induced reactions, the new silicon-detector array SONIC with 8 ΔE-E-telescopes was installed inside the existing γ array HORUS consisting of 14 HPGe detectors. The main purpose of the combined setup will be the study of inelastic scattering experiments using p, d and α beams delivered by the Cologne 10 MV Tandem accelerator. Since the excitation of the target nucleus is uniquely determined by the energy loss of the projectile, gates on the excitation of specific levels or on a certain final level can be set. Due to the angular granularity of SONIC and HORUS, angular correlations between the ejectile and the emitted γ ray can be measured, which gives access to the spin of the level. Using the particle identification capabilities, light ejectiles (p to α) can be easily distinguished, allowing the study of weaker reaction channels, e.g. inelastic scattering, even if the cross section is dominated by others, e.g. transfer reactions. As a first physics test case, the reaction ⁹²Mo(p,p'γ) was measured. Preliminary results of this experiment are shown, concentrating on states and decay properties of the Pygmy Dipole Resonance.

[en] The combined setup SONIC and HORUS consists of the γ-ray spectrometer HORUS with 14 HPGe detectors and the recently commissioned particle spectrometer SONIC with up to 8 ΔE-E silicon detectors. This setup is used to measure the ejectile of a nuclear reaction (p, d, t, or α) in coincidence with the deexciting γ rays emitted by the recoil nucleus. By requiring a certain ejectile energy (e.g. the excitation of a level), a very clean γ spectrum is obtained, in which only physically related events remain. Measuring the angular correlations between the coincident ejectiles and γ-rays allows spin assignments to excited nuclear levels by comparison to theoretical particle-γ angular correlations. An overview of the experimental setup is given, and preliminary p-γ angular correlations measured in a recent ⁹²Mo(p,p'γ) experiment are shown.

[en] The SONIC rate at HORUS setup of the Institute for Nuclear Physics in Cologne is used to investigate the low-energy response of the nucleus. Low spin states, e.g., the pygmy dipole resonance, can be studied by performing inelastic proton scattering reactions. An important observable for the investigation of these modes is the γ branching ratio which can be accessed with the setup. Furthermore, spins and parities can be assigned by measuring the angular correlation of the ejectile and the deexciting γ-ray. The obtained experimental distribution is in good agreement with the distorted wave Born approximation (DWBA). In this contribution, the results for the experimental angular distributions of the reaction ⁹⁴Mo(p,p'γ)⁹⁴Mo as well as the corresponding theoretical description are shown.

[en] The Pygmy Dipole Resonance (PDR) has been studied extensively in the past decade. However, one important property, the γ-decay branching ratio to excited states, is still not known systematically. To access this observable, the particle-γ coincidence method is used at the dedicated SONIC rate at HORUS setup. It consists of up to twelve silicon detectors for particle identification and ejectile energy determination and the 14 HPGe detector array HORUS for high-resolution γ-ray spectroscopy. Due to the good energy resolution of the silicon detectors, a narrow gate on a specific excitation energy can be set, which allows for a sensitive and straightforward state to state determination of branching ratios. Branching ratios for 1^- states in ⁹²Mo and ⁹⁴Mo from (p,p^'γ) experiments and the decay pattern of 1^- states in ¹²⁰Sn from a (d,pγ) experiment will be shown, as well as possible theoretical interpretations. Together with γ-decay studies from the γ³ setup at HIγS, these experiments allow for a systematic study of the PDR decay pattern to better understand the underlying structure of low-lying E1 strength.

[en] The experimental evidence for the presence of octupole vibrational states in ¹⁶⁸Yb is presented. In order to populate the excited states in this nucleus, the ¹⁶⁶Er(α,2nγ)¹⁶⁸Yb fusion evaporation reaction was used with a beam energy of 24 MeV. Using the coincidence method, the level scheme was corrected and extended up to 3 MeV, both for the positive and negative parity states. In a second step, the lifetimes of five excited states were measured by using the fast timing method with the Bucharest HPGe and LaBr₃:Ce detector array using the triple-γ coincidence method. Reduced E1 and E2 transition probabilities were extracted from the measured lifetimes and compared, when possible, with similar observables in neighboring isotopes, showing a smooth behavior with increasing mass. The positive and negative-parity states revealed by this experiment are compared with the Interacting Boson Model and are found to be in good agreement.

[en] A ¹¹⁹Sn(d,pγ) experiment was performed using the combined setup SONIC rate at HORUS at the 10 MV FN Tandem accelerator in Cologne. The excitation of states in the region of the Pygmy Dipole Resonance (PDR) via this neutron-transfer reaction was investigated in detail. The setup consisted of 14 HPGe and 6 ΔE-E silicon telescope detectors, allowing an offline selection of excitation and deexcitation channels due to the coincident detection of γ-rays and charged particles. Data show a clear excitation of states in the PDR region and several states in this region were identified as J=1 states by comparison to data from a Nuclear Resonance Fluorescence (NRF) experiment. Individual branching ratios could be determined, shedding more light on the internal structure of the PDR. By normalizing the relative excitation in the (d,pγ) reaction to the B(E1) values extracted from NRF, a splitting into two groups of states seems evident, which might hint at a different single-particle character of these groups. This contribution presents the (d,pγ) experiment and all observables determined. Furthermore, results are put into context by comparison to data from other experiments, i.e., NRF and (p,p') experiments.

[en] The excitation of states belonging to the Pygmy Dipole Resonance (PDR) in ¹²⁰Sn was observed in a ¹¹⁹Sn(d,pγ) experiment, using the SONIC rate at HORUS setup at the 10 MV Tandem accelerator in Cologne. The setup, consisting of 6 ΔE-E silicon and 14 HPGe detectors, allows a selection of reaction, excitation, and deexcitation channels in an offline analysis, due to complete kinematics. Several excited states were identified as J^π = 1^(-) states by comparison with results from a nuclear resonance fluorescence experiment, establishing the (d,p) reaction as an additional tool to study the PDR. Preliminary analysis shows that a γ-decay branching to the first 2⁺ state is observed and branching ratios can be determined. The contribution presents the experiment and principles of the data analysis needed to select transitions from J^π = 1^- states. Furthermore, the latest status of the analysis is presented, including branching ratios and branching-corrected B(E1) values, which will allow a more stringent comparison with recent inelastic proton scattering data.

[en] Low-lying electric dipole strength, often denoted by Pygmy Dipole Resonance (PDR), is still not understood in detail. One important observable which could shed light on this is the γ-decay branching ratio to excited states. However, this observable is still only known for a few cases. The SONIC rate at HORUS setup in Cologne allows to measure branching ratios with high sensitivity. It consists of twelve silicon detectors for particle identification and ejectile-energy determination and the 14 HPGe detector array HORUS for high-resolution γ-ray spectroscopy. Using this setup, the particle-γ coincidence method is employed at the 10 MV FN tandem accelerator. Since the silicon detectors have a good energy resolution (70 keV in-beam) and a high solid-angle coverage (9%), a narrow gate on a specific decay and reaction channel gives a straightforward, state-to-state determination of branching ratios. Branching ratios for 1^- states in ^92,94Mo, ⁶⁰Ni, and ¹²⁰Sn are presented. Combining these experiments with γ-decay studies from the γ³ setup at HIγS, it is possible to investigate the decay pattern of the PDR systematically and to gain more insight into the underlying structure of low-lying E1 strength.

[en] In the last decade, the Pygmy Dipole Resonance (PDR) has attracted a lot of interest both in experimental and theoretical nuclear physics. However, some key observables are still not easily accessible. One of these is the decay branching of the PDR to excited states, which is a sensitive measure of the wave functions. To gain access to this observable, the new setup SONIC rate at HORUS consisting of silicon and HPGe detectors at the Institute for Nuclear Physics in Cologne was used to investigate the two molybdenum isotopes "9"2Mo and "9"4Mo in inelastic proton scattering experiments. In these experiments, both the energy of the γ-ray and of the particle were measured in coincidence with high energy resolution and in the offline analysis, specific excitation and de-excitation patterns were studied. The results of the "9"2Mo(p,p'γ) experiment are presented, giving insight into the state-to-state decay behaviour of the PDR. Additionally, preliminary results of the "9"4Mo(p,p'γ) experiment will be shown, focussing on the same observable for this non-magic nucleus.