The Coincidence Doppler-shift attenuation method (CDSAM) after proton scattering is a well-established technique for determining nuclear-level lifetimes in the range of sub-picoseconds. In recent years, several (p,p'γ) experiments have been performed utilizing the combined detector array SONIC@HORUS consisting of 14 HPGe detectors and 12 silicon detectors. To complement the well-established analysis procedure, a reverse method was tested. A first benchmark analysis was conducted on 130 Te, showing good agreement. Furthermore, spectroscopy and level-scheme construction are feasible due to the coincidence conditions enabled by γ- as well as particle-detection using SONIC@HORUS. Preliminary results on 104 Ru obtained by inelastic proton scattering and the fundamental principles of the reverse approach benchmarked on 130 Te, will be presented.

Low-lying excited levels in 116Te were studied by measuring level lifetimes with the recoil-distance Dopplershift method in the 112Sn(12C, 8Be) 116Te alpha-transfer reaction and angular correlations following the beta decay of 116I. Both experiments were performed at the Cologne FN Tandem accelerator. Several new levels were discovered below 3.2 MeV excitation energy, spins and multipole mixing ratios were determined via angular correlations. Lifetimes were measured for the 2+1 , 0+2 , 22+, and 4+1 and upper limits for lifetimes were determined for higher lying levels. The experimental findings are compared to calculations in the U(5) limit of the interacting boson model and are also discussed in the framework of shape coexistence which is expected in midshell Te isotopes.

While the general properties of the electric dipole (E1) strength below the neutron separation energy are well known, there are still open questions about its underlying structure. In a previous 119Sn(d, p-y) experiment, a grouping of the Pygmy Dipole Resonance was observed depending on the excited 1 particle -1 hole structures. This prompted similar investigations on the other applicable isotopes, 115,117Sn. Here, first results and a comparison to (-y,-y') data are presented.

The influence of nuclear shape deformation on the Pygmy Dipole Response (PDR) was investigated using (α,α′γ) scattering on 144 Sm and 154 Sm. Experiments were conducted at iThemba LABS, coupling for the first time the K600 magnetic spectrometer with the BaGeL (Ball of Germanium and LaBr detectors) array. Preliminary results showcasing the efficacy of the facility and set-up for performing these 0° scattering experiments to investigate the PDR region are presented.

The timing performance of the integrated digital constant fraction discriminators of the two digitizer modules V1730 and V1751 from CAEN are systematically investigated with respect to fast-timing lifetime measurements. Systematic and parameter-dependent knowledge of the time walk behavior and the time resolution of the digital constant fraction discriminators is obtained. Understanding these dependencies is crucial for properly calibrating individual fast-timing systems and a comparable investigation of these digitizers was never conducted before. Reference is made to the existing analog standard for fast-timing techniques and recent digital developments. The study shows, that the timing performance of both modules is comparable to other digital fast-timing implementations and established fast-timing setups using analog constant fraction discriminators, but with the added benefit of digital processing. The peculiarities of the modules are pointed out and described. Both digitizer modules were found to be highly effective and user-friendly instruments for modern fast-timing requirements. Best parameter sets for both digitizers as well as best energy application ranges are provided.

Background: The Z=52 nuclei Te-128 and Te-130 are interesting candidates to study nuclear-structure properties close to the Z=50 shell. The knowledge of lifetimes of low-lying states in those nuclei is still scarce. Purpose: The goal of the present work is to extend the experimental database of nuclear level lifetimes of low-spin states in Te-128 and Te-130. Methods: Nuclear level lifetimes were determined by means of the Doppler-shift attenuation method (DSAM) using p-gamma coincidences measured at the SONIC@HORUS setup located at the FN-Tandem ion accelerator of the University of Cologne. Results: For Te-128, lifetimes of eleven excited states could be determined, one of these for the first time. For the case of Te-130, 18 nuclear level lifetimes were obtained, 15 for the first time. In both experiments, upper limits for lifetimes of several additional levels were determined. Moreover, the nuclear level scheme of Te-130 could be extended. One additional level and 13 new transitions for levels above 2.7 MeV have been added. A standard shell-model calculation was performed and compared with the experimental results, showing an overall agreement. Conclusions: DSAM using p-gamma coincidences is a powerful tool to determine lifetimes in the subpicosecond range free of feeding contributions. Although both experiments yielded low statistics, numerous lifetimes could be obtained. The use of p-gamma coincidences furthermore enables the extension of level schemes.

The E2/M1 multipole mixing ratio of the 1(sc)(+) -> 2(1)(+) gamma-ray transition and therefore the F-vector E2 decay of the scissors mode of the shape-phase transitional nucleus Sm-152 have been measured with the nuclear resonance fluorescence method at the High-Intensity gamma-ray Source (HI gamma S). Furthermore, parity quantum numbers of several dipole-excited states have been remeasured, making use of the polarized gamma-ray beam at HI gamma S, and partially reassigned. The new data enable an unambiguous determination of the proton and neutron effective boson quadrupole charges within the proton-neutron interacting boson model. With the well-constrained parameter set, a new mixed-symmetry state is predicted.

The well-known spherical-deformed-transitional nucleus and potential 0 nu beta beta emitter Nd-150 and its daughter Sm-150 were investigated in nuclear resonance fluorescence experiments using quasimonoenergetic, linearly polarized gamma-ray beams. For both nuclei transitions from the 1(+) scissors mode to the 0(2)(+) and 2(2)(+) states were observed for the first time and their respective M1 transition strengths were determined. Through a systematic investigation, a sensitivity of these transition strengths to the three Majorana parameters of the interacting boson model-2 (IBM-2) was established. In combination with the novel experimental data, this poses strong constraints to the Majorana parameters in improved IBM-2 representations of both nuclei. A subsequent recalculation of the nuclear matrix elements (NMEs) for the Nd-150 -> Sm-150 0 nu beta beta decay in the IBM-2 with these improved representations results in M-IBM-2((0)nu beta beta) [0(1)(+)] = 3.35 for the NME for 0 nu beta beta decay into the ground state of Sm-150 and M-IBM-2((0)nu(beta beta)) [0(2)(+)] = 1.30 for 0 nu beta beta decay to its 0(2)(+) state.

The microscopic structure of the low-energy electric dipole response, commonly denoted as pygmy dipole resonance (PDR), was studied for ^{120}Sn in a ^{119}Sn(d,pγ)^{120}Sn experiment. Unprecedented access to the single-particle structure of excited 1^{-} states below and around the neutron-separation threshold was obtained by comparing experimental data to predictions from a novel theoretical approach. The novel approach combines detailed structure input from energy-density functional plus quasiparticle-phonon model theory with reaction theory to obtain a consistent description of both the structure and reaction aspects of the process. The presented results show that the understanding of one-particle-one-hole structures of the 1^{-} states in the PDR region is crucial to reliably predict properties of the PDR and its contribution to nucleosynthesis processes.

Background: Superdeformed (SD) bands are suggested by theory around Ca-40 and in lighter alpha-conjugate nuclei such as Mg-24, Si-28, and S-32. Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca-40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. The key evidence of superdeformation would be the observation of transitions with high B(E2) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si-28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in Si-28 were populated in the Si-28(alpha, alpha') reaction using a 130-MeV He-4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9.1 degrees to favor the population of states with J approximate to 4. Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr3 detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si-28 in the vicinity of 10 MeV. However, while the candidate 4(+) SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2(+) SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B(E2) < 43 W.u. could be established. This contradicts AMD predictions of approximate to 200 W.u. for such a transition. Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in 28 Si represents an SD band, which demonstrates the potential of the methodology devised here.

The dipole response of the proton-magic nucleus 124Sn 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 124Sn 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 γ -decay behavior of excited states were studied. The 124Sn(p,p’γ ) experiment was performed at Ep = 15 MeV using the combined spectroscopy setup SONIC@HORUS at the Tandem accelerator of the University of Cologne. Proton-γ coincidences were recorded, enabling a state-to-state analysis due to the excellent energy resolution for both particles and γ rays. J = 1 states in the PDR region were populated in the present inelastic proton scattering experiment. Many γ -decay branching ratios could be determined.

The nuclear astrophysics setup at the Institute for Nuclear Physics, University of Cologne, Germany is dedicated to measurements of total and partial cross sections of charged-particle induced reactions at astrophysically relevant energies. These observables are key ingredients for reaction network calculations of various stellar scenarios, and crucial for the understanding of the nucleosynthesis of elements. The experiments utilize the high-efficiency γ-ray spectrometer HORUS, and the 10 MV FN-Tandem accelerator. An updated target chamber as well as further experimental methods established in the last years will be presented which allow to measure cross sections down to the nb region. The reliability of the measured cross sections is proven by a 89Y(p, γ)90Zr commissioning experiment. Additionally, an application for nuclear astrophysics will be presented. The results of a 93Nb(p, γ)94Mo experiment will be discussed as well as their deviations compared to formerly reported results.

This paper illustrates the principle of the Doppler-shift attenuation method (DSAM) using particle-γ coincidences, a method for determining lifetimes of excited nuclear levels in the range of few femtoseconds up to one picosecond. The coincident detection holds several advantages towards conventional DSAM experiments, such as the elimination of background and feeding transitions. Using the experimental data on 94 Zr, the concept of the (p,p’γ) DSAM analysis is presented. Additional experimental results are highlighted.

New experimental data on the neutron single-particle character of the Pygmy Dipole Resonance (PDR) in ^{208}Pb are presented. They were obtained from (d,p) and resonant proton scattering experiments performed at the Q3D spectrograph of the Maier-Leibnitz Laboratory in Garching, Germany. The new data are compared to the large suite of complementary, experimental data available for ^{208}Pb and establish (d,p) as an additional, valuable, experimental probe to study the PDR and its collectivity. Besides the single-particle character of the states, different features of the strength distributions are discussed and compared to large-scale shell model (LSSM) and energy-density functional plus quasiparticle-phonon model theoretical approaches to elucidate the microscopic structure of the PDR in ^{208}Pb.

An inelastic proton scattering experiment was performed with the combined setup SONIC@HORUS at a beam energy of 15 MeV in Cologne. First results for the deduced branching ratios as well as the E1 strength distribution obtained with the Sn(p, p′γ) reaction are presented. Additionally, a qualitative comparison to excitations in experiments with different probes like (α, α′γ) and (γ, γ′) will be discussed.

The high-spin structures of Ba-136 and Ba-137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Ba-136 is populated in a Xe-136 + U-238 MNT reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and in two Be-9 + Te-130 fusion-evaporation reactions using the High-efficiency Observatory for gamma-Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the B-11 + Te-130 fusion-evaporation reaction utilizing the HORUS gamma-ray array. The level scheme above the J(pi) = 10(+) isomer in Ba-136 is revised and extended up to an excitation energy of approximately 5.5 MeV. From the results of angular-correlation measurements, the E-x = 3707- and E-x = 4920-keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both Te-132 and Xe-134 are characterized by high-energy 12(+) -> 10(+) transitions, the Ba-136 E2 ground-state band is interrupted by negative-parity states only a few hundred keV above the J(pi) = 10(+) isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in Ba-137. The new results close a gap along the high-spin structure of N < 82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130, and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character.

An inelastic proton scattering experiment was performed with the combined setup SONIC@HORUS at a beam energy of 15 MeV in Cologne. First results for the deduced branching ratios as well as the E1 strength distribution obtained with the Sn-124(p, p'gamma) reaction are presented. Additionally, a qualitative comparison to excitations in experiments with different probes like (alpha, alpha'gamma) and (gamma, gamma') will be discussed.