Table of contents

This volume contains the lectures and short talks given at the XVIII International School on Nuclear Physics, Neutron Physics and Applications. The School was held from 21 to 27 September 2009 in Hotel 'Lilia' located on 'Golden Sands' (Zlatni Pyasaci) Resort Complex on the Black Sea coast, near Varna, Bulgaria. The School was organized by Institute for Nuclear Research and Nuclear Energy of Bulgarian Academy of Sciences. Co-organizer of the School was Bulgarian Nuclear Regulatory Agency. The event was sponsored by National Science Fund of Bulgaria.

According to the long-standing tradition the School has taken place every second year since 1973. The School content has been restructured according to our new enlarged international links and today it is more similar to an international conference than to a classical nuclear physics school. This new image attracts a lot of young scientists and students from many countries. This year – 2009, we had the pleasure to welcome more than 50 distinguished scientists as lecturers. Additionally, 14 young colleagues received the opportunity to present a short contribution. The program ranges from recent achievements in nuclear structure and reactions to the hot problems of the application of nuclear methods, reactor physics and nuclear safety. The 94 participants enjoyed the scientific presentations and discussions as well as the relaxing atmosphere at the beach and the pleasant evenings.

The main topics were the following:

• Nuclear excitations at various energies.

• Nuclei at high angular moments and temperature.

• Structure and reactions far from stability

• Symmetries and collective phenomena

• Methods for lifetime measurements

• Astrophysical aspects of nuclear structure

• Neutron nuclear physics

• Nuclear data

• Advanced methods in nuclear waste treatment

• Nuclear methods for applications

Several colleagues contributed to the organization of the School. We would like to thank to them and especially to the Scientific Secretary of the School Dr Dimitar Tonev, members of Organizing Committee Professor Sevdalina Dimitrova and Dr Dimitar Tarpanov for their cordiality and high level assistance.

Professor Dr Sc Ch Stoyanov Professor Dr Sc N Janeva Sofia, 12 November 2009 Co-chairs of the Organizing Committee

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We consider the phase space moments (or Wigner Function Moments (WFM)) method, which is developed to describe the collective motion. The method is generalized to take into account pair correlations. Its connection with RPA and Green's function method is analyzed in the simple model, the Harmonic Oscillator with Quadrupole–Quadrupole (HO+QQ) interaction. Possibilities of WFM method are demonstrated on an example of the nuclear scissors mode.

An importance sampling iterative algorithm, developed few years ago, for generating exact eigensolutions of large matrices is upgraded so as to allow large scale shell model calculations in the uncoupled m-scheme. By exploiting the sparsity properties of the Hamiltonian matrix and projecting out effectively the good angular momentum, the new importance sampling allows to reduce drastically the sizes of the matrices while keeping full control of the accuracy of the eigensolutions. Illustrative numerical examples are presented.

The level ordering in the unbound nuclei ¹⁰Li and ¹³Be is established on a firm basis using a time dependent projectile fragmentation model, comparing to experimental data and using structure inputs obtained from a semi-phenomenological core-vibration coupling model of two-neutron halo nuclei. The information on the shell ordering corresponds to the understanding of the neutron-core interaction. This is a building block of any three body model of borromean nuclei. As a consistency test we show that the energy spectra of some Beryllium isotopes obtained by using pp-RPA predict the same shell ordering as extracted from the reaction model vs. data analysis and that the well known structure of ¹¹Li is reproduced.

We report on a shell-model study of nuclei with four valence nucleons in the ¹³²Sn and ²⁰⁸Pb regions. This aims at investigating to what extent the striking similarity existing between the low-energy properties of ¹³⁴Sb and ²¹⁰Bi persists when adding a pair of identical particles. We employ realistic low-momentum effective interactions derived from the CD-Bonn nucleon-nucleon potential through use of the V_low-k approach. The calculated results are in very good agreement with the available experimental data and emphasize the persistence of a close resemblance between the spectroscopy of the two regions when moving away from the one proton-one neutron systems.

Within the Higher Tamm Dancoff Approximation (HTDA), single particle states associated with a mean field of the Hartree-Fock type are used into shell model like calculations. Recently, this approach has been used for ground state calculations in magic nuclei and in the N = Z mass region, as well as to study properties of some important isomeric states. The Cranking version of this formalism (Cr. HTDA) represents an attempt to reproduce rotational bands up to high spins in heavy nuclei. In this context, through the use of the mean field part of HTDA, many deformation and rotation effects (as intruder orbitals and effects of the time reversal symmetry breaking) are included in the configuration space. This work discusses the Cr. HTDA results obtained for two Pb isotopes (in order to test the approach), when using up to 2 particles – 2 holes excitations and provides tests for enlargement of the configuration space by 4 particle – 4 holes excitations. It is focused on the configuration space properties, improvement of truncation schemes, computational problems and saturation behavior of some physical quantities.

The SU(3) symmetry-adapted version of the No-Core Shell Model (NCSM), which reduces to the Elliott SU(3) Model in its 0ℏω limit, is described and shown to be effective in providing an efficient description of low-lying eigenstates of ¹²C and ¹⁶O. A symmetry-guided framework is suggested based on our recent findings of low-spin and high-deformation dominance in realistic NCSM results. This holds promise to significantly enhance the reach of ab initio shell models.

A systematic study of low energy nuclear structure at normal deformation has been carried out using the Generator Coordinate Method mapped onto a 5-Dimensional Collective quadrupole Hamiltonian (5DCH) by using the Gaussian Overlap Approximation (GCM-GOA). The collective space is spanned by Hartree Fock Bogoliubov (HFB) states under axial and triaxial quadrupole constraints deduced with the D1S Gogny force. In addition, our 5DCH includes the Thouless-Valatin dynamical corrections to its rotational kinetic terms. The work is described in detail elsewhere together with the corresponding comparisons with experimental data when it is available. Many properties show a satisfactory agreement with experiment, but there is an almost systematic overestimation of vibrational band head energies, which is the subject of the present paper. We show here the performance of the theory on related observables, and propose improvements of the theory to address the problem of the vibrational band heads. An important reason for the deficient is the treatment of vibrational inertial parameters. In particular, the theory needs to include the dynamical Thouless-Valatin corrections to the vibrational terms in the 5DCH. In present work, on the aim of a simple formula grounded by known symmetry rules within the 5DCH, these dynamical TV corrections are roughly estimated, allowing us to handle their possible effects in term of spectroscopic properties, to present a guess of the next model improvment, and to isolate some areas in the chart where states I_n^π = 0⁺₂, 2⁺₂ or 2⁺₃ seem to have important components out of the scope of a pure collective quadrupole approach.

A basis of multiphonon states is generated by constructing and solving iteratively a set of equations of motion. Represented in this basis, the Hamiltonian has a simple structure and can be easily brought to diagonal form. The method is adopted to compute the energy levels and the electromagnetic responses in ¹⁶O, chosen as test ground because of its complex structure.

The effect of parity mixing in the single particle (s.p.) states of odd-mass nuclei with quadrupole-octupole deformations is examined through a reflection-asymmetric deformed shell model. A strong coupling scheme between the parity mixed s.p. state and a coherent quadrupole-octupole vibration mode in the core is considered. The Coriolis decoupling factor is obtained in a projected form corresponding to the good total parity of the system. The average parity of the s.p. state and the decoupling factor are evaluated in several nuclei as functions of the quadrupole and octupole deformation parameters β₂ and β₃. It is found that the average s.p. parity obtains various dominant (+ or −) values in the (β₂,β₃)-plane, while the s.p. wave function is strongly fragmented into components with different parities. It is shown that by comparing the behaviour of the decoupling factor in the (β₂,β₃)-plane to values obtained in a collective quadrupole-octupole model one can determine physically reasonable regions for the deformation parameters.

Density functional theory provides a very powerful tool for a unified microscopic description of nuclei all over the periodic table. It is not only successful in reproducing bulk properties of nuclear ground states such as binding energies, radii, or deformation parameters, but it also allows the investigation of collective phenomena, such as giant resonances and rotational excitations. However, it is based on the mean field concept and therefore it has its limits. We discuss here two methods based based on covariant density functional theory going beyond the mean field concept, (i) models with an energy dependent self energy allowing the coupling to complex configurations and a quantitative description of the width of giant resonances and (ii) methods of configuration mixing between Slater determinants with different deformation and orientation providing are very successful description of transitional nuclei and quantum phase transitions.

The structure of the ¹⁸O nucleus at excitation energies above the α decay threshold was studied using ¹⁴C+α resonance elastic scattering and (⁷Li,t) a-transfer reactions. A number of states with large α reduced widths have been observed, indicating that the a-cluster degree of freedom plays an important role in this N≠Z nucleus. A 0⁺ state with an α reduced width exceeding the single particle limit was identified at an excitation energy of 9.9±0.3 MeV. We discuss evidence that states of this kind are common in light nuclei and give possible explanations of this feature. Also, the astrophysical implications of the cluster structure of ¹⁸O is discussed.

Generalized parton distributions (GPDs) offer a comprehensive picture of the nucleon struture and dynamics and provide a link between microscopic and macroscopic properties of the nucleon. These quantities, which can be interpreted as the transverse distribution of partons carrying a certain longitudinal momentum fraction of the nucleon, can be accessed in deep exclusive processes. This lecture reviews the main features of the nucleon structure as obtained from elastic and inelastic lepton scatterings and unified in the context of the GPDs framework. Particular emphasis is put on the experimental methods to access these distributions and the today experimental status.

Very little is known about clustering in heavy nuclei and in particular the interaction between the correlated cluster nucleons and remaining core nucleons. Currently the phenomenological Saxon-Woods plus cubic Saxon-Woods core-cluster potential successfully predicts the alpha decay half-life and energy band spectra of a number of heavy nuclei. This model, however, lacks a microscopic understanding of clustering phenomenon in these heavy nuclear systems. A fully relativistic microscopic formalism is presented, which generates the core-cluster potential by means of the McNeil, Ray and Wallace based double folding procedure. The core and cluster baryon densities are calculated by using a relativistic mean field approach. The Lorentz covariant IA1 representation of the nucleon-nucleon interaction is folded with the core and cluster densities. Theoretical predictions of the ground-state decay half-life and positive parity energy band of ²¹²Po are obtained with the relativistic mean field formalism and which are compared to the results from the phenomenological Saxon-Woods plus cubic Saxon-Wood core-cluster potential and microscopic M3Y interaction.

An extended analysis of the reaction mechanisms involved in the deuterons interaction with light and medium nuclei, ²⁷Al and ^63,65Cu, at incident energies from 3 to 60 MeV starting with elastic scattering until the evaporation from fully equilibrated compound system is presented. An increased attention is devoted to the breakup mechanism, all its components, the elastic, inelastic (fusion), and total breakup, being carefully analysed. Moreover, the corresponding stripping mechanism contribution to the (d, p) and (d, n) reaction cross sections through population of the discrete levels of the residual nuclei, was calculated. Finally, following the decay path, the pre-equilibrium and evaporation cross sections, corrected for the breakup and stripping decrease of the total reaction cross section, have completed the deuteron activation cross sections analysis. The overall agreement between the measured data and model calculations proves the correctness of nuclear mechanism description taken into account for the deuteron-nucleus interaction.

An accurate description of the nuclear response functions for neutrino scattering in the Gev region is essential for the interpretation of present and future neutrino oscillation experiments. Due to the close similarity of electromagnetic and weak scattering processes, we will review the status of the scaling approach and of relativistic modeling for the inclusive electron scattering response functions in the quasielastic and Δ-resonance regions. In particular, recent studies have been focused on scaling violations and the degree to which these imply modifications of existing predictions for neutrino reactions. We will discuss sources and magnitude of such violations, emphasizing similarities and differences between electron and neutrino reactions.

The theory of Faddev/AGS few body reaction frameworks is presented. A comparison with other reaction formalisms (DWBA, CDCC) is made. Sucesses and shortcomings of the scattering approaches for breakup are analysed. Some set of calculated reaction observales for resonant and nonresonant breakup are presented to obtain insight into the physics incorporated on the scattering approaches.

Three- and four-body scattering is described in the framework of exact Faddeev-type integral equations. They are solved numerically using momentum-space partial-wave basis. The Coulomb interaction between charged particles is included using a novel implementation of the screening and renormalization method. The technique is applied to three- and four-nucleon scattering. Furthermore, the method has been extended successfully to elastic, transfer, and breakup reactions in three-body-like nuclear systems. Examples are deuteron scattering on stable nuclei ranging from ⁴He to ⁵⁸Ni and proton scattering on weakly bound two-body system such as ¹¹Be, ¹⁵C, and ¹⁷O. These calculations allow to evaluate the accuracy of traditional approximate nuclear reaction approaches like the continuum-discretized coupled-channels (CDCC) method but also to test novel dynamical models such as nonlocal optical potentials.

It is known the fusion cross section plays crucial role in the choice of the reaction to synthesize new superheavy elements. An estimation of the fusion cross section in the reactions with massive nuclei is difficult task when the mass (charge) and angular distributions of the quasifission and fusion-fission fragments strongly overlap. The measured yields of evaporation residues, fusion-fission and quasifission fragments in the ⁴⁸Ca+¹⁵⁴Sm reactions are analyzed in the framework of the method based on the dinuclear system concept and advanced statistical model. The experimental data of the fission fragments are decomposed into contributions coming from fusion-fission, quasifission, and fast fission. Our investigations showed the synthesis of the new element Z=120 (A=302) is more preferable in the ⁵⁴Cr+²⁴⁸Cm reaction in comparison with the ⁵⁸Fe + ²⁴⁴Pu and ⁶⁴Ni+²³⁸U reactions because the excitation function of the evaporation residues of the former reaction is some orders of magnitude larger than that for the last two reactions.

Studies of peripheral (quasi-elastic and deep-inelastic) collisions near the Fermi energy are presented with a two-fold goal: first, to produce very neutron-rich nuclei towards the neutron drip line and, second, to obtain insight into the underlying dynamics and the nuclear equation of state (EOS). Towards the first goal, our studies indicated an enhanced production of neutron-rich nuclides suggesting that peripheral reactions at Fermi energies offer a novel way to access very neutron-rich rare isotopes in unexplored regions of the nuclear chart. Towards the second goal, we have made comparisons of our experimental data to detailed calculations using the semiclassical microscopic model CoMD (Constrained Molecular Dynamics). The CoMD code implements an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) or K=380 (stiff EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential and imposes a phase space constraint to restore the Pauli principle during the collision. Present results from these comparisons are consistent with a soft equation of state (K=200) with a rather stiff density dependence of the symmetry potential (symmetry energy).

The determination of closed analytical solutions of the Morse potential for nonzero angular momenta has been an open problem for decades, solved recently by the Asymptotic Iteration Method (AIM) for solving differential equations. Closed analytical expressions have been obtained for the energy eigenvalues of the Bohr Hamiltonian in the γ-unstable case, as well as in an exactly separable rotational case with γ ≈ 0, called the exactly separable Morse (ES-M) solution. All medium mass and heavy nuclei with known β₁ and γ₁ bandheads have been fitted by using the two-parameter γ-unstable solution for transitional nuclei and the three-parameter ES-M for rotational ones. It is shown that bandheads and energy spacings within the bands are well reproduced for more than 50 nuclei in each case. Comparisons to the fits provided by the Davidson potential, also soluble by the AIM, are made.

After reviewing some basic features of the temperature-governed phase-transitions in macroscopic systems and in atomic nuclei we consider non-thermal phase-transitions of nuclear structure in the example of cluster states. The vibron model, as the algebraic model of the relative motion, is considered from this aspect. The extension by the coupling to the internal degrees of freedom of the clusters is discussed. Phenomenological and semimicroscopical algebraic cluster models with identical interactions are applied to binary cluster systems of closed and non-closed shell clusters. A phase-diagram for the binary cluster systems is proposed, as well as its relation to that of the shell-model. The role of the quasi-dynamical symmetry, as a possible signature of the phase of a finite quantum system, is supported.

Shape isomers, including superdeformed and hyperderformed states can be determined from the quasi-dynamical SU(3) symmetry based on the Nilsson-model. We investigate the possible binary clusterizations of these shape isomers. The allowed cluster-configurations give a hint for the favourable reaction channels for populating these states. Our semimicroscopic approach is largely based on symmetry considerations, combined with energetic preference calculations. As illustrative examples some results for the ³⁶Ar, ⁴⁰Ca and ⁵⁶Ni nuclei are shown.

The sextic oscillator is applied as a γ-independent potential to describe the energy spectrum of nuclei in regions where the occurrence of E(5) symmetry has been assumed. Experimental levels of Ru, Pd, Cd, Te, Xe and Ba isotopes have been assigned to model states characterized by the ξ = 1, 2 quantum numbers, and the two model parameters a and b have been determined from a least square fit procedure. The resulting potentials have a spherical or deformed minimum. Most of the typical E(5) candidates, i.e. ¹⁰⁴Ru, ¹⁰²Pd, ^106,108Cd and ¹²⁴Te correspond to parameters lying close to the parabola separating the two domains in the a − b plane.

The evolution of the ground-state nuclear shapes with the number of nucleons is studied within a self-consistent Hartree-Fock-Bogoliubov formalism based on Gogny and Skyrme density-dependent interactions. Potential energy surfaces including triaxial degrees of freedom are studied in various isotopic chains. Signatures for the E(5) critical point symmetry are analyzed in Pd, Xe, and Ba isotopes, while those for the X(5) are studied in Nd, Sm, Gd, and Dy isotopes. Oblate to prolate shape transitions are also studied in Yb, Hf, W, Os, and Pt isotopic chains. The transitions are discussed in terms of the deformation dependence of the single-particle energies.

Two methods for measuring lifetimes of excited states in nuclei are discussed. One recently developed method involves a plunger device and inverse kinematics Coulomb excitation with heavy beams. The other method covers a different lifetime range and relies on electronic timing. Both methods have recently been applied at Yale University. This paper will give a brief overview of technical aspects of those measurements. A short motivation and preliminary results of the experiments are given.

The chiral interpretation of twin bands in odd-odd nuclei is investigated in the Interacting Boson Model framework. The analysis of the wave functions shows that the possibility for angular momenta of the valence proton, neutron and core to find themselves in the favorable, almost orthogonal geometry is present, but not dominant. Such behavior is found to be similar in nuclei where both the level energies and the electromagnetic decay properties display the chiral pattern, as well as in those where only the level energies of the corresponding levels in the twin bands are close together. The difference in the structure of the two types of chiral candidates nuclei can be attributed to different β and γ fluctuations, induced by the exchange boson-fermion interaction, i.e. by the antisymmetrization of odd fermions with the fermion structure of the bosons. In both cases the chirality is weak and dynamic. Among the nuclei that are candidates for chiral behavior, the best candidate is probably the odd-even ¹³⁵Nd, where the β and γ fluctuations are strongly reduced and chirality, although dynamic in origin, is rather close to the static limit.

A variational approach for many-body systems due to Balian and Vénéroni, which goes beyond the Harrtree-Fock mean field, has been implemented in the case of nuclear Skyrme effective interactions used in examining large amplitude collective motion. An evaluation of the numerical issues involved with the method is presented, in which it is found that the effect of model parameters is generally under control, but long-time running leads to unphysical results.

The isospin symmetry-breaking corrections δ_c obtained with the self-consistent relativistic RPA approaches are presented. It is shown that the proper treatment of the Coulomb mean field is very important for extracting these corrections. The nucleus-independent Ft value, the V_ud matrix element and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix are discussed. The effects of neutron-proton mass difference on the isospin symmetry-breaking corrections are also investigated.

The quasiparticle-phonon model using a separable interaction deduced from a Skyrme force is adopted to compute low-lying spectra and the giant dipole resonance in the N = 80 isotones. It is shown that the Skyrme interaction not only reproduces the fragmentation of the giant resonance but also yields results comparable to the ones obtained when a Woods-Saxon potential is used in the description of the mixed symmetry states recently discovered in these nuclei. This test is encouraging in view of future extensions of the method to neutron-rich nuclei far from stability.

The significant progresses of the chirality in atomic nuclei are briefly reviewed for both experimental and theoretical sides. A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core and applied to investigating the chirality in odd-A nucleus ¹³⁵Nd. Static chirality has been shown to be a transient phenomenon surrounding by chiral vibrations. It is found that the B(M1) staggering is associated strongly with the characters of nuclear chirality, i.e., the staggering is weak in chiral vibration region while strong in the static chirality region.

The low-lying 0⁺ excited states remain an object of particular interest in the nuclear structure physics. Recently long sets of 0⁺ excited states were experimentally observed. Our analysis of the experimental data have shown that in even-even nuclei of the rare-earth and actinide regions the energies of all low lying 0⁺ excited states with great accuracy can be distributed on parabolic functions of the number of monopole excitations building these states. Along with the classification of the energies of the 0⁺ excited states in respect to the number of bosons that build the band heads we analyze the role of their collectivity in the structure and evolution of the yrast bands and the B(E2) transition probabilities within these bands. The experimental determination in ¹⁶⁰Dy of the predicted in this way 0⁺ excited state with energy 0.6813 MeV is presented.

A microscopic approach to calculate the optical potential (OP) with the real part obtained by a folding procedure and with the imaginary part inherent in the high-energy approximation is applied to study the ⁸He+p elastic scattering at energies of tens of MeV/nucleon (MeV/N). The OP's and the cross sections are calculated using different models for the neutron and proton densities of ⁸He. The role of the spin-orbit potential is studied. Comparison of the calculations with the available experimental data on the elastic scattering differential cross sections at beam energies of 15.7, 26, 32, 66 and 73 MeV/N is performed. The problem of the ambiguities of the depths of each component of the optical potential is considered by means of the imposed physical criterion related to the known behavior of the volume integrals as functions of the incident energy. It is shown also that the role of the surface absorption is rather important, in particular for the lowest incident energies (e.g., 15.7 and 26 MeV/N). The present approach, which uses only parameters that renormalize the depths of the OP, can be applied along with other methods using microscopically calculated optical potentials.

Binary reactions at energies close to the Coulomb barrier received recently a significant boost thanks to the advent of the large solid angle magnetic spectrometer PRISMA coupled to the γ array CLARA. In the present paper different aspects of the recent results of nuclear structure and reaction dynamics will be presented, focusing more closely on the reaction mechanism.

In series of recent theory articles, predictions have been formulated suggesting the existence of nuclear states whose mean-field Hamiltonians and thus the implied geometrical shapes, are characterized by tetrahedral symmetry. Following these publications, series of experiments for the Rare-Earth region have been proposed and performed. In this article, we shortly summarize the theory evolution developed in the original articles and discuss the status of the issue in light of the preliminary results of the ongoing experimental analyses. More recent theoretical results cross checked with extended literature investigations, suggest that the Actinide region might contain the best experimental candidates to investigate the fingerprints of the symmetry. A proposition is made to prove it via lifetime measurements with the so-called "microwave method".

In ⁹⁸Cd a new high-energy isomeric γ-ray transition was identified, which confirms previous spin-parity assignments and enables for the first time the measurement of the E2 and E4 strength for the two decay branches of the isomer. Preliminary results on the ⁹⁸Cd high-excitation level scheme are presented. A comparison to shell-model calculations as well as implications for the nuclear structure around ¹⁰⁰Sn are discussed.

Pb(,γ') photon scattering reactions were studied [1] with the nearly monochromatic, linearly polarized photon beams at the High Intensity γ-ray Source (HIγS) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of ^206,207,208Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle-core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements.

Relative and absolute E0 transition strengths [ρ² (E0)] on the transitional path between the X(5) solution and the rigid rotor limit have been evaluated [1] within the framework of the Confined β-Soft (CBS) rotor model. Relative E0 transition strengths between the β-vibrational band and the ground state band decrease with increasing angular momentum for a given potential stiffness. The Z-independent quantity X ∝ ρ²(E0; 0⁺₂ → 0⁺₁)/B(E2; 0⁺₁ → 2⁺₁) has been traced between X(5) and the rigid rotor. It reaches the value 4β²_M at the rigid rotor limit, as previously derived by Rasmussen. A new Inter-Band E0 − E2 correlation observable Y ∝ ρ²(E0; 0⁺₂ → 0⁺₁)/B(E2; 0⁺₂ → 2⁺₁)² has be en proposed, which is independent on the absolute nuclear deformation and solely depends on the nuclear stiffness. Available data for X and Y are in satisfactory agreement with the CBS model.

The large solid angle magnetic spectrometer for heavy ions PRISMA, installed at Laboratori Nazionali di Legnaro (LNL), was operated up to the end of March 2008 in conjunction with the highly efficient CLARA set-up. It allowed to carry out nuclear structure and reaction mechanism studies in several mass regions of the nuclide chart. Results obtained in the vicinity of the island of inversion and for the heavy iron and chromium isotopes are presented in this contribution. The status of the new focal plane detectors specifically designed for light ions and slow moving heavy ions is also reported.

Considerable progress has been achieved recently in the experimental investigation of quadrupole-collective isovector excitations in the valence shell, the so called mixed-symmetry states (MSSs), in the mass A ≈ 130 region. This is due to a new experimental technique for study MSSs which is based on the observation of low-multiplicity γ-ray events from inverse kinematics Coulomb excitation with the large 4π spectrometer, such as Gammasphere. The obtained experimental information for the MSSs of stable N = 80 isotones indicates that for low-collective vibrational nuclei the underlying single-particle structure can be the most important factor for preserving or fragmenting the MSSs through the mechanism of shell stabilization. The evolution of the MSSs from ¹³⁴Xe to ¹³⁸Ce is also used to determine the local strength of the proton-neutron interaction derived for first time from states with symmetric and antisymmetric nature.

Low-lying collective vibrational excitations of ⁹²Zr have been investigated with electron scattering at the S-DALINAC. The form factors of isospin polarized one-quadrupole phonon states of ⁹²Zr at the Z = 40 proton subshell closure have been measured and the momentum-transfer dependence of the form factors for the one-quadrupole phonon states have been compared to the prediction of the Quasiparticle Phonon Model. The E2 transition strengths of the one-quadrupole phonon states and the E3 transition strength of the one-octupole phonon state have been extracted. A comparison to the data on ⁹⁴Mo and previous spectroscopic information on mixed-symmetric states (MSSs) of ⁹²Zr will be given.

The collective nuclear rotation, at high spins and as a function of temperature T, is investigated in the transition region between the regular ordered motion at T=0 and the chaotic compound nucleus regime around the particle binding energy. The experimental analysis, based on statistical techniques, is carried out in nuclear systems characterized by specific quantum numbers (such as K) and deformation (as for example superdeformed nuclei). Data from high statistics EUROBALL experiments are discussed, focusing on nuclear structure effects at the onset of the chaotic regime. The experimental findings are compared to prediction from a Montecarlo simulation of the γ-decay flow based on microscopic cranked shell model calculations at finite temperature.

Reactions induced by halo and loosely bound stable nuclei at low bombarding energies, arouse a lot of interest in the last fifteen years. Many experiments have been performed so far, using both stable and radioactive beams. These experiments are driven by theoretical expectations concerning effects, at sub-barrier energies, of coupling between relative motion and intrinsic excitation of the colliding nuclei which for the weakly bound systems lies into the continuum. In this paper some results of experiments concerning the study of reaction mechanisms with halo and loosely bound stable nuclei at energies around the Coulomb barrier will be discussed.

Absolute transition probabilities are fundamental observables for nuclear structure. The recoil-distance-Doppler-shift (RDDS) technique, also called plunger technique, is a well established tool for the determination of these important experimental quantities via the measurement of lifetimes of excited nuclear states. Nowadays nuclear structure investigations are concentrated on exotic nuclei which are often produced with extremely small cross sections or with very low beam intensities. In order to use the RDDS technique also for the investigation of very exotic nuclei this method has to be adapted to the specific needs of these special reactions. This article gives an overview on recent RDDS measurements with the new differential plunger in combination with particle detectors and recoil spectrometers. These were done with projectile multistep Coulomb excitation at low beam energies (≈ 5 MeV/u) and at intermediate beam energies (≈ 100 MeV/u) using one step Coulomb excitations and knockout reactions.

In order to perform half-life measurements at Alto, we developed a fast-timing setup using fast scintillators : LaBr₃. The main components of our setup and their characteristics (timing properties) are presented. The resulting time resolution, obtained after optimization, and measured off-line with radioactive sources is discussed. This set-up was tested on-line by measuring using the slope method half-lives of ^137–139Cs levels fed by the β⁻ decay of ^137–139Xe. The neutron-rich Xe nuclei were produced by ²³⁸U photofission using, at low intensity, the electron beam and the line of the future facility ALTO. Our results show the ability of such a fast-timing system to measure half-lives lower than the total time resolution. Off-line and on-line results are discussed.

The first phase of the AGATA project, namely the AGATA Demonstrator Array, consists of a subset of 5 triple clusters of the final array and will be used to demonstrate the feasibility of the γ-ray tracking. The performance of the instrument has been estimated up to now only through Monte Carlo simulations and indirect measurements. The first installation is presently ongoing ay the Laboratori Nazionali di Legnaro, Italy, where it has replaced the CLARA array at the target position of the PRISMA magnetic spectrometer. In the present contribution, the details of the installation will be reviewed and preliminary results from the first in-beam commissioning test will be given.

The Saci-Perere spectrometer of the University of São Paulo has been configured to perform particle-gamma coincidence measurements in order to study nuclear reaction mechanisms. The motivation of this type of measurement comes from the recent development of nuclear reaction models based on the São Paulo potential with the inclusion of an imaginary part with no adjustable parameters. New preliminary data on the ¹⁸O+¹¹⁰Pd transitional system are presented, and apparent similarities to weakly bound cases (e.g.⁷Li + ¹²⁰Sn) are briefly discussed.

The triple alpha reaction α+α+α → ¹²C + γ is considered to be the most relevant one in stars at the helium burning stage, since it permits to bridge the A=5 and A=8 instability gaps. However, at higher temperatures and neutron rich environments, other reactions can also play a relevant role. In this work we investigate the astrophysical reaction and production rates for the two-particle radiative capture processes α+n+n → ⁶He+γ and α+α+n → ⁹Be+γ. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. The four-body recombination reactions α+α+n+n → ⁶He + α, α + n + n + n → ⁶He + n, α+α+n+n → ⁹Be + n and α + α + α + n → ⁹Be + α are also investigated as a possible alternative as a source of ⁶He and ⁹Be.

The Trojan Horse method (THM) is a powerful indirect technique that provides a successful alternative path to determine the bare nucleus astrophysical S(E) factor for rearrangement reactions down to astrophysical energies. This is done by measuring the cross section for a suitable three body process in the quasi-free kinematics regime. Prescriptions and basic features will be presented together with some applications to demonstrate how THM works.

The ¹⁰B(n,α₀)⁷Li and ¹⁰B(n,α_iγ)⁷Li angular distributions have been measured at the GELINA time-of-flight spectrometer in the incident neutron energy range from 0.1 keV to 1 MeV by means of a twin Frisch-grid ionization chamber. With this type of detector it is possible to measure the angular distribution of the charged reaction fragments in a close to 2×2π solid angle with ~100% efficiency and a clear separation of both reaction channels: emission to the ⁷Li ground state (α₀) or to its first excited state (α₁). A strong angular anisotropy was observed at ~ 520 keV. In order to extend the energy range up to 2.5−3 MeV and to measure, also, the reaction cross sections, a double twin Frisch-grid ionization chamber was constructed. It is loaded with two very thin 94% ¹⁰B-enriched samples, mounted back-to-back with ²³⁵U samples on the common cathodes. New data acquisition, visualization and analysis software is used in a new set of long-term measurements, which are still going on.

In this work we present results from the characterization of both LaCl₃:Ce scintillation and polycrystalline diamond detectors to be used for measurements of prompt gamma radiation emitted in fission. The properties of these new detector types, such as excellent timing resolution and improved energy resolution will allow to obtain fission data with higher accuracy than those available today.

It is known that uncertainties in the calculation of characteristics of power nuclear reactors such as critical sizes, power density field, reactor life time etc are caused mainly (about 40 %) by uncertainties in the knowledge of neutron constants of reactor materials. Allowed errors on neutron constants for all basic reactor materials and fission products are about 1–5 %. Required errors on constructional materials should be in the range of 5–10 % for σ_t, σ_s, σ_γ and from 2 to 12 % for self-shielding factors. The required accuracy on neutron constants for the majority of reactor materials is not achieved up to now and consequently it is necessary to continue experimental research in this direction. For example, such an accuracy could be achieved using the multiplicity spectrometry technique of the gamma-rays. The description of this method, its features and several experimental results will be presented.

The "Energy Plus Transmutation"-setup consists of a thick cylindrical lead target of 456 mm length and diameter of 84 mm, which is surrounded by a thick layer containing 206,4 kg of natural uranium. This small-sized target-blanket-assembly resembles the geometry and the constituents of an industry-sized subcritical system for power production and nuclear waste transmutation. The irradiations of the target-blanket-assembly are performed using deuteron beams of variable energies, delivered by the Nuclotron accelerator at the Joint Institute for Nuclear Research in Dubna. Using precision gamma-spectroscopy, the amounts of isotopes of bismuth, lead and thallium, produced in the lead target during the irradiation with a deuteron beam of 2,52 GeV [1,2] have been determined. The collected data on the isotope production are compared with the predictions of nuclear-reaction- and particle-transport-codes.

The full-scale scientific research complex IREN will comprise a 200-MeV linear accelerator LUE-200 with a beam power about 10 kW, a subcritical multiplying target, and beam infrastructure with experimental pavilions, as well as technological, control, safety and service systems. The characteristics of the full-scale complex IREN (integral neutron yield 10¹⁵n/s and pulse width 0.6 μs) will allow it to rank among the best neutron sources of such class GELINA (Belgium) and ORELA (USA). The realization of the project is conducted in several stages. The first stage includes the construction of the LUE-200 linear accelerator and nonmultiplying target. This will make possible to carry out experiments which require precision neutron spectroscopy in the energy range from fractions of eV to hundreds of eV already at the first stage of IREN. The results of the physical start-up of the first stage of IREN facility at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research are presented. General scheme and current status of the electron linac are described. Achieved parameters are: pulsed electron beam current – 2.0 A; electron energy – 30 MeV; pulse width – 100 ns; repetition rate – 25 Hz; integral neutron yield (3÷5)•10¹⁰ n/s.

The total neutron cross section of cadmium (Cd) is very large in the thermal neutron energy region which determines its special role in reactor technology. The first resonance of ¹¹³Cd at 0.178 eV is of high importance in the interpretation of Cd neutron cross section structure in the thermal region. The evaluated data files for Cd isotopes and particularly the resonance parameters do not correspond to the requirements of the advanced reactor technologies. To provide data for a new evaluation, a set of top quality transmission experiments has been designed and performed at the neutron time-of-flight facility GELINA at the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. The measurements have been carried out at 26.45 m and 50 m flight paths of GELINA at 50 Hz, 400 Hz and 800 Hz working frequencies of the LINAC, using natural Cd samples with various thicknesses (purity 99.99% in Cd). The experiments at 50 Hz provide high quality data in the thermal energy region, from which we could extract the resonance parameters for the first resonance of ¹¹³Cd at 0.178 eV with high accuracy.

Considering the transmission data obtained with various sample thicknesses as a source of additional information for low level cross section we validate a new approach for cross section description in this energy region.

The PDF gives the full list of participants.