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The neutron time-of-flight facility GELINA installed at the IRMM Geel (13) has been designed to study neutron-induced reactions in the resonance region. It is a multi-user facility, providing a pulsed white neutron source, with a neutron energy range between 10 meV and 20 MeV and a time resolution of 1 ns. The research program concentrates on cross section data needs for nuclear energy applications. In this paper efforts to improve the quality of cross section data for neutron induced capture reactions in the resolved and unresolved resonance region are presented together with examples of cross section data to support the development of advanced reactor concepts and to optimize the use of present nuclear power plants.

Neutron capture gamma rays were measured for all stable Se isotopes in an incident neutron energy region from 15 to 100 keV. A neutron time‐of‐flight method was adopted with a ns‐pulsed neutron source based on the 7Li(p,n)7Be reaction and with a large anti‐Compton NaI(Tl) spectrometer. A pulse‐height weighting technique was applied to the observed capture gamma‐ray pulse‐height spectra to obtain the capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of stable Se isotopes were derived with an error of about 5%. The capture gamma‐ray spectra were obtained by unfolding the observed capture gamma‐ray pulse‐height spectra. The present results for the capture cross sections are compared with the previous measurements and the evaluations of JENDL‐3.3 and ENDF/B‐VI.8 and VII.0.

Systematic cross section measurements of alpha‐capture reactions at sub‐Coulomb energies relevant to the p process were performed in the Ge‐Sn region. At the same time a recent global α‐nucleus optical model potential (OMP) based on the double‐folding method was updated using all existing data on alpha elastic scattering and alpha‐induced reactions. In this paper, we report on our recent measurements of alpha‐capture reactions and present calculations using the improved alpha‐nucleus OMP.

Excited states in 124Xe have been studied via the 12C(124Xe,124Xe*) Coulomb excitation reaction. Relative cross‐sections have been determined from the γ‐ray yields observed with Gammasphere. The E2 strengths between the low‐spin states in 124Xe have been determined. The results clearly show the realization of the O(5) symmetry even for the off‐yrast states with high τ, while the O(6) symmetry seems to be already broken.

Understanding the nuclear structure of 152Sm, along with other N = 90 isotones, has long posed a challenge. A rapid transition in shape between the spherical N = 88 150Sm and well‐deformed N = 92 154Sm is observed, along with strong evidence for shape coexistence. Competing ideas have been put forward over the decades, with the most recent being that N = 90 is at the critical point of a shape phase transition. Until recently, the lack of high‐precision data has not allowed the competing models to be extensively tested. In a coordinated program of investigation, a series of complementary experiments, which include high‐statistics β decay, multi‐step Coulomb excitation, the 150Nd(α,2n) reaction, and the (n,n′γ) reaction, have been performed for 152Sm. These experiments have revealed the existence of a pairing‐isomer band, a hexadecapole band, the lack of multi‐phonon β vibrational bands, and the repetition of structures built on the first excited Kπ = 0+ as built on the ground state. The status of these coo...

We are developing a new method to identify nuclear levels based on neutron capture reactions, named “TELLA‐2.” Measured data of prompt gamma rays from 33S(n,γ)34S was used to improve the method. We will show how we obtain candidates of nuclear levels.

It has been shown that the (3He,t) charge exchange reaction at intermediate energies, used at zero momentum transfer in combination with high‐resolution magnetic spectrometers is a very powerful probe for Gamow‐Teller strengths. Several N = Z nuclei such as 46V [1] or 50Mn [2] have been investigated. Recently ab‐initio nuclear structure calculations have become possible for light nuclei. Thus experimental studies on light nuclei have become of great current interest [3]. We review previous results obtained in 11C with respect to nuclear structure aspects and the Hoyle state, and present some early results of a 9Be(3He,t)9B experiment carried out recently, pointing out the significance of high‐resolution charge‐exchange reactions and the investigation of Gamow‐Teller strengths for the understanding of nuclear structure in light nuclei.

We report on systematic investigations of low‐lying electric dipole (E1) strength in atomic nuclei. Using the method of real photon scattering the dipole response of all stable N = 82 isotones has been measured with high resolution. In all cases a resonance like structure of E1 strength is observed in the energy region 5–8 MeV, which shows a strong fragmentation. The total integrated strength increases towards the proton poorer isotones, indicating a dependence of the total strength on the neutron‐to‐proton ratio. The experimental results are compared to microscopic calculations within the Quasi‐particle Phonon Model (QPM). By including complex configurations of up to three phonons the calculation is able to reproduce also the fragmentation of the E1 strength and is in good agreement with the experimental observation.

Low‐lying collective states in 136Ba were investigated with (n,n′γ) techniques, including Doppler‐shift attenuation lifetime measurements. The level spins, lifetimes, branching ratios, multipole‐mixing ratios and transition strengths reveal candidates for symmetric‐phonon states up to third order. The 2ms+ mixed‐symmetry state was confirmed as unfragmented and a candidate for a [21+⊗2ms+]3+ two‐phonon mixed‐symmetry state is proposed.

The rate of the 17F(p,γ)18Ne reaction is of significant importance in astrophysical events like novae and x‐ray bursts. A 3+ state in 18Ne predicted to dominate the rate was found at 599.8 keV using the 17F(p,p)17F reaction [1], but the resonance strength was unknown. For the first time, the 17F(p,γ)18Ne reaction has been measured directly with the Daresbury Recoil Separator, using a mixed beam of radioactive 17F and stable 17O from the HRIBF at ORNL. A γ width was found for the 599.8 keV resonance in 18Ne, and an upper limit on the direct capture S factor was determined at an intermediate energy of 800 keV.

Resonances in the 12C(16O,γ)28Si radiative capture process at energies around the Coulomb barrier have been probed using the very selective 0° Dragon spectrometer at Triumf and its associated BGO γ‐array. For the first time the full level scheme involved in this process has been measured and shows previously unobserved γ‐decay to doorway states around 11 MeV in 28Si.

We extend the classical Landau theory for rotating nuclei and show that the backbending in 162Yb, that comes about as a result of the two-quasiparticle alignment, is identified with the second order phase transition. We found that the backbending in 156Dy, caused by the instability of $\gamma$-vibrations in the rotating frame, corresponds to the first order phase transition., Comment: 4 pages, 2 figures

Thermal neutron capture gamma-ray spectra for {sup 187}Re(n,{gamma}){sup 188}Re reaction were measured. Singles and coincidence spectra were detected in order to develop the level scheme. The evaluation is in progress, of which the first results are obtained from the analysis of coincidence spectra, allowing to check the level scheme below 500 keV excitation energy. Seven low-energy negative parity bands are developed in order to find better energies for rotational levels. With a good confidence, a few positive parity bands are developed as well. Rotor plus two quasiparticle model calculations, employing effective matrix element method are performed for the system of six negative parity rotational bands.

High quality radioactive beams have recently made possible the measurement of (d,p) reactions on unstable nuclei in inverse kinematics, which can yield information on the development of single-neutron structure away from stability, and are of astrophysical interest due to the proximity to suggested r-process paths. The Oak Ridge Rutgers University Barrel Array (ORRUBA) is a new high solid-angular coverage array, composed of two rings of silicon detectors, optimized for measuring (d,p) reactions. A partial implementation has been used to measure (d,p) reactions on nuclei around the N = 82 shell closure.

New measured differential cross sections of tritons and alpha particles following the 6Li(n,t)α reaction are reported for incident neutron energies between 0.2 and approximately 20 MeV. The neutrons were produced by spallation at the WNR facility at the Los Alamos Neutron Science CEnter (LANSCE), with the incident neutron energy determined by the time‐of‐flight method. Four E‐ΔE telescopes were used at eight laboratory angles. These data have been incorporated into a prior R‐matrix fit for the compound 7Li system, and result in an (n,t) reaction cross section that is 4% to 10% higher than previous evaluations in the 1–3 MeV incident neutron energy region.

Existing experimental data on γ decay of energy levels in medium‐weight and heavy nuclei at excitation energies well above the pairing gap indicate that the role of nuclear structure effects is small and that this decay is largely governed by the extreme statistical model. Specifically, in line with the validity of Brink hypothesis and the paradigm of photon strength, the average properties of the γ decay can be described by a set of photon strength functions (PSFs) for individual multipolarities and by the level density function. PSFs are directly related to the photoabsorption cross sections σγ abs. It is well known that in the case of E1 radiation this cross section is dominated by the giant dipole electric resonance. However the size of σγ abs. and its γ‐ray energy dependence at energies below the neutron threshold are known rather poorly. In the case of higher multipolarities (M1, E2,…) the present knowledge about their roles is much worse. Available information on E1 and M1 PSFs obtained from variou...

Starting from an effective Skyrme interaction we present the finite rank separable approach for the quasiparticle random phase approximation. The approach is generalized to take into account the residual particle‐particle interaction. As an illustration of the method properties of the low‐lying quadrupole states in the even‐even nuclei around 132Sn are studied.

By using an empirical power law function with two fit parameters, the multiplet splitting for more than 30 pure particle‐hole states (with values between −0.3 and +0.6 MeV) is described with a residual energy difference of about 0.03 MeV.

A search for an anomalous n‐p scattering from a polyethylene sample (CH2) at 8 final energies between 64 eV and 2.5 keV was carried out. The scattering intensities were compared to that from a graphite (C) sample. The results were found to confirm our previous n‐p results on H2O at a final energy of 24.3 keV where no n‐p scattering anomaly was observed. The present results refute all proposed models attempting to explain the occurrence of any n‐p scattering anomaly at keV neutron energies.

We present evidence of the existence of a new supersymmetric quartet of nuclei in the A=190 mass region. The analysis is based on new experimental information on the odd-odd nucleus 194Ir from transfer and capture reactions. The new data allow the identification of a new supersymmetric quartet, consisting of the 192,193Os and 193,194Ir nuclei. We make explicit predictions fo r193Os, and suggest that its spectroscopic properties be measured in dedicated experiments. Finally, we study correlations between different transfer reactions.

The advantages of using inelastic neutron scattering with detection of the emitted γ rays, i.e., the (n,n′γ) reaction, for exploring the structure of stable nuclei are reviewed. Examples of the information available with these techniques are provided and progress in understanding multiphonon excitations is described. The unique nuclear structure of 94Zr is discussed.

Positron‐electron pair creation near the threshold energy is extremely difficult to investigate by both experiments and theory. First test experiments were performed at the ILL to determine the cross sections for positron‐electron pair creation near threshold using prompt γ‐rays from different targets after neutron capture and conventional radioactive sources. Pair creation was studied in a Ge detector, which simultaneously acted as sample and detector. First results are presented which show a significant deviation from theoretical values near threshold.

An improved extrapolation method for shell model calculations is presented. By axially symmetric bases, computation is drastically simplified.

Understanding the origin, structure, and phases of hadronic matter is a forefront research area in physics. An integral part of this challenge is to achieve realistic modeling of the complex dynamics of atomic nuclei, which is key to comprehending the evolution of the universe from a fundamental quark/gluon level. We recently demonstrated the potential power of an innovative concept, the ab initio symplectic no‐core shell model (Sp‐NCSM), based on expanding the conventional harmonic oscillator basis in terms of the symmetry‐adapted and physically relevant symplectic basis, to reach new domains of nuclear structure. Using realistic interactions tied to Quantum Chromo‐dynamics (QCD), the Sp‐NCSM approach holds promise to build the bridge from QCD to measured properties of light nuclei, predict diverse features of unstable nuclei crucial for astrophysical processes, and provide nuclear structure information essential for cosmology and probing physics beyond the standard model.

Multipole mixing ratios for transitions between excited 2+ states and the 21+ state in 140Nd are measured using angular correlation techniques for beta decay reactions. Two transitions with dominant M1 components are identified, and the higher‐lying 2+ states involved in these transitions are presented as candidates for the one‐phonon mixed‐symmetric 2+ state in 140Nd. Assuming pure two‐state mixing between the one‐phonon 2+ state and a presumed three‐phonon symmetric state yields a mixing matrix element between these states, which is discussed in terms of shell effects on mixed‐symmetric behavior in the N = 80 isotones.

Lifetimes and g‐factors have been measured for short‐lived low‐lying states in 70Zn using the techniques of projectile Coulomb excitation in inverse kinematics combined with transient magnetic fields and the Doppler‐Shift‐Attenuation‐Method (DSAM). While the g(21+) value was redetermined and found to be consistent with the literature values, all other data are new. The main goal is a better understanding of the influence of the v(g9/2) orbital in this region of the nuclear chart.

We propose an approach to nuclear pairing at finite temperature and angular momentum. This approach includes the effects due to the quasiparticle‐number fluctuation and dynamic coupling to pair vibrations within the self‐consistent quasiparticle random‐phase approximation. The pairing gaps, total energies, and heat capacities are calculated within a doubly folded multilevel model as well as several realistic nuclei. The results obtained show that, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out. This is manifested in a thermal pairing gap, which does not collapse at a critical temperature predicted by the conventional Bardeen‐Cooper‐Schrieffer’s (BCS) theory, but has a tail extended to high temperatures. Moreover, this approach also predicts the appearance of a thermally assisted pairing at finite angular momentum. The effect of backbending of the momentum of inertia as a function of the square of angular velocity is also discussed.

We study the structure of isomeric state 21+ in the odd‐odd N = Z nucleus 94Ag using a shell model, which is capable of describing the spectra of upper g9/2‐shell nuclei close to the N = Z line. It is shown that the 21+ state becomes isomeric because of level inversion of the 19+ and 21+ states due to core excitations across the N = Z = 50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. In the present shell model calculation, however, the large‐deformation picture of Mukha et al. in Nature 439, 298 (2006) cannot be accepted.

Using the HORUS spectrometer at the Cologne FN‐TANDEM accelerator, we performed a γγ coincidence measurement on 88Zr. The reaction used was 89Y(p,2n)88Zr. A particular point of interest was the search for a potential 2+ mixed‐symmetric state. In the experiment, we measured the multipole mixing ratios of the decays of the 22+ and the 23+ states and determined the energies of the 23+ and 02+ states precisely. Furthermore, we found two new levels and seven new γ transitions.

We propose a novel way of determining the Hamiltonian of the Interacting Boson Model (IBM), based on the Mean‐field theory. The quadrupole deformations in a fermion system, indicated by a Potential Energy Surface (PES) obtained by the constrained Skyrme Hartree‐Fock calculations, are mapped, to a good approximation, onto the appropriate boson system. A merit is that levels and wave functions of excited states are calculated with the exact treatments of angular momentum and particle number. The validity of the process is examined for Sm and Ba isotopes, and predictions are made for unexplored territories on the nuclear chart, namely the right‐lower corner of 208Pb.

Energies and electromagnetic transitions in 16O are evaluated by an equation of motion method which generates iteratively a microscopic multiphonon basis and solves exactly the nuclear eigenvalue problem in such a basis. The computed quantities are greatly affected by the multiphonon configurations and by the center of mass motion, here completely removed.

Using the Advanced Time‐Delayed method we have studied transition rates in several neutron‐rich nuclei at the magic shell closures. These include the heavy Co and Fe nuclei just below the Z = 28 shell closure at the point of transition from spherical to collective structures. Of particular interest is 63Fe located exactly at the point of transition at N = 37. A substantial increase in the information on this nucleus was obtained from a brief fast timing study conducted at ISOLDE. The new results indicate that 63Fe seems to depart from a simple shell model structure observed for heavier N = 37 isotones of 65Ni and 67Zn.Another region of interest are the heavy Cd and Sn nuclei at N = 72, 74 and the properties of negative parity quasi‐particle excitations. These experiments, performed at the IGISOL separator at Jyvaskyla, revealed interesting properties of the E2 rates in the sequence of E2 transitions connecting the 10+, 8+, 6+, 4+, 2+ and 0+ members of the multiplet of levels in 122Sn due to neutrons in th...

An essential property of collectivity is the proton‐neutron degree of freedom, that leads to the so‐called states of mixed symmetry. Predictions for the electromagnetic decay of the lowest‐lying mixed‐symmetry state 2MS,1+ in vibrator‐like even‐A nuclei are a strong M1 decay to the fully‐symmetric 21+ state and a weak collective E2 decay to the ground state 01+. Excited states in 62Zn have been studied via the 61Ni(3He,2nγ) reaction using the HORUS‐cube spectrometer of the Institute for Nuclear Physics in Cologne. Two fragments of the mixed‐symmetry state 2MS,1+ could be identified by determining absolute M1 transition strengths to the 21+ state.

For fissile actinide targets 233U, 235U and 239Pu the capture cross sections are strongly influenced by the target spin, fission transition states spectroscopy and fission/γ‐emission competition of the compound nuclides. The capture cross sections were obtained via a consistent description of fission and elastic/inelastic scattering, (n,γf) reaction being included.For neutron capture reactions on even‐even U, Pu and Cm nuclei the methods, proven in case of 232Th(n,γ) and 238U(n,γ) data analysis are used. Calculated 240Pu(n,γ) and 244Cm(n,γ) reaction cross sections shapes are much similar to that, observed for the 238U(n,γ) and 232Th(n,γ) reactions. Differences are due to fission and neutron emission competition, which depends on the (Z,N)‐composition of the compound nucleus.

The neutron time‐of‐flight facility GELINA installed at the IRMM Geel (B) has been designed to study neutron‐induced reactions in the resonance region. It is a multi‐user facility, providing a pulsed white neutron source, with a neutron energy range between 10 meV and 20 MeV and a time resolution of 1 ns. The research program concentrates on cross section data needs for nuclear energy applications. In this paper efforts to improve the quality of cross section data for neutron induced capture reactions in the resolved and unresolved resonance region are presented together with examples of cross section data to support the development of advanced reactor concepts and to optimize the use of present nuclear power plants.

International audience; We use a new approach based on image reconstruction techniques to improve model-based predictions of nuclear masses. A partial view image pattern is built by taking the differences between experimentally measured masses and the predictions given by different theoretical models which describe the smooth macroscopic behavior. We show that it is possible to significantly improve predictions in regions not too far from measured nuclear masses.

The lifetimes of excited states of the 122Ba ground—state band, populated via the 108Cd(16O,2n)122Ba and the 112Sn(13C,2n)122Ba reactions, have been measured using the Recoil Distance Doppler—Shift method. The level scheme of 122Ba has also been revised.

The N = 52 nucleus 98Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler‐shift method (RDDS) and with the Cologne HORUS spectrometer for a γγ angular correlation experiment. For the first time lifetimes of yrast states and highly excited low‐spin states were measured in 98Pd and the low‐spin level scheme was extended. From our data we were able to interpret 98Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones 94Mo and 96Ru due to its closeness to doubly‐magic 100Sn.

Electromagnetic dipole absorption cross‐sections of transitional nuclei with large‐amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of instantaneous‐shape sampling. The concept bases on the slow shape dynamics as compared to the dipole vibrations. The dipole strength is calculated by means of RPA for the instantaneous shapes, the probability of which is obtained by means of IBA‐1. Very good agreement with the experimental absorption cross sections near the nucleon emission threshold is obtained.

The impact of the ground‐state quantum phase transitions on the evolution of excited levels in the critical parameter region is discussed. The analysis is focused on systems with first‐ and second‐order transitions and is illustrated by the cusp and nuclear collective Hamiltonians.

Recently, an Orange spectrometer, a focusing iron‐free magnetic spectrometer, has been installed at a beam line of the 10 MV Tandem accelerator of the IKP of the University of Cologne. The high efficiency of 15% of 4π for the detection of conversion electrons and the energy resolution of 1% makes the Orange spectrometer a powerful instrument. From the conversion electron spectrum, transition multipolarities can be determined using the so called K to L ratio. In combination with an array of germanium and lanthanum bromide detectors, e−‐γ‐coincidences can be performed to investigate the level scheme. Moreover, the very fast lanthanum bromide scintillator with an energy resolution of 3% allows e−‐γ lifetime measurements down to 0.3 ns. A second Orange spectrometer can be added to build the Double Orange Spectrometer for e−‐e−‐coincidences. It is indispensable for lifetime measurements of low intensity or nearby lying transitions as often occur in odd‐A and odd‐odd nuclei. The capabilities are illustrated wit...

To benchmark the validity of using the (d,pγ) reaction as a surrogate for (n,γ), the 171,173Yb(d,pγ) reactions were measured with the goal to reproduce the known neutron capture cross section ratio of these nuclei. Preliminary surrogate results reproduced the measured values within 15%.

High‐resolution inelastic electron scattering experiments were performed at the S‐DALINAC for a precise determination of the partial pair width Γπ of the second Jπ = 0+ state, the so‐called Hoyle state, in 12C. Results for the monopole matrix element (directly related to Γπ) from a nearly model‐independent analysis based on an extrapolation of low‐q data to zero momentum transfer are presented. Additionally, a Fourier‐Bessel analysis of the transition form factor is discussed. The combined result of both methods leads to a pair width Γπ62.2(10) μeV.