abstract

In spite of the heading, these approaches to nuclear structure physics are not in any contrast. They approach the problem of nuclear structure from opposite directions. We believe, however, that when many-body calculations will achieve their final goal, we will eventually understand why the simple shell model works so well and where it fails. The shell model has been used extensively and successfully for almost 60 years. It is still not understood why it is such a good approximation.

abstract

We report on a shell-model study of nuclei with two valence nucleons in the \(^{132}\)Sn and \(^{208}\)Pb regions, focusing attention on the similarity between the spectroscopy of these two regions. In our study we make use of realistic effective interactions derived from the CD-Bonn nucleon–nucleon potential renormalized by use of the \(V_{{\rm low}-k}\) approach. We show that the behavior of the proton–proton, neutron–neutron and proton–neutron multiplets in \(^{134}\)Te, \(^{134}\)Sn and \(^{134}\)Sb, respectively, is quite similar to that of the analogous multiplets in the counterpart nuclei in the \(^{208}\)Pb region, \(^{210}\)Po, \(^{210}\)Pb and \(^{210}\)Bi.

abstract

We discuss observable features of exceptional points and the resonance spectroscopy of \(^{16}\)Ne using the Shell Model Embedded in the Continuum.

abstract

The shell structure of the nucleus implies the existence of magic numbers. Since several years many indications have been accumulated, theoretically as well as through experiments at various laboratories around the world, that if one moves away from stability, the location of the magic numbers shifts as an inescapable consequence of the evolving nature of the nuclear force itself. In this respect, it is the balance between the tensor and spin-orbit components that seems particularly instrumental. Illustrative examples from recent experiments at Ganil, at the neutron-rich and proton-rich side of the nuclear chart for \(N\) or \(Z\) equal 20 or 28, will be presented here.

abstract

Isomeric decays in the heavy even–even Cd isotopes populated in the fragmentation of \(^{136}\)Xe as well as projectile fission of \(^{238}\)U have been studied within the RISING project at GSI. The new experimental results suggest an energy of 1325 keV for the first excited 2\(^+\) state in semi-magic \(^{130}\)Cd and confirm the previously established positions of this state in \(^{126}\)Cd and \(^{128}\)Cd (652 keV resp. 645 keV). The origin of the unexpectedly low 2\(^+\) excitation energies in the \(N=78, 80\) isotopes has been investigated in detail performing modern beyond mean field calculations employing the Gogny force.

abstract

New level structures are proposed for neutron-rich \(^{127,129,131}\)In populated in the decay of \(^{127,129,131}\)Cd. No evidence for the presence of 1-parti- cle-2-hole intruder structures in the neutron-rich In isotopes is observed.

abstract

The \(\beta \)-decay properties of neutron-rich fission fragments of Cu, Zn, and Ga isotopes were studied at the Holifield Radioactive Ion Beam Facility. Beams of \(^{75-79}\)Cu, \(^{79-81}\)Zn, and \(^{83-85}\)Ga were formed and delivered to two new end-stations at the facility. The Low-energy Radioactive Ion Beam Spectroscopy Station is a traditional on-line low energy (200 keV) beam line with 4 clover Ge detectors, two half-cylindrical plastic \(\beta \)-detectors, and a moving tape collector. In addition, many of the beams were accelerated to above 2 MeV/u and delivered to a micro-channel plate and transmission ion chamber located just in front of the same detector setup. In both cases, fine adjustment of an isobar separator was used to enhance the isotope of interest. Excited levels in the daughters and \(\beta \)-delayed neutron branching ratios were measured and used to confirm isotope identification. The decays from \(^{79}\)Cu and \(^{85}\)Ga were observed for the first time as was the \(^{84}\)Ge \(2_1^+\) level populated by \(\beta \) and \(\beta \)n decay channels.

abstract

The large solid angle magnetic spectrometer PRISMA coupled to the \(\gamma \) array CLARA represents a significant step forward in the field of binary reactions at energies close to the Coulomb barrier. With this set-up extensive investigations have been carried out for nuclear structure and reaction dynamics. Via \(\gamma \)-particle coincidences it is now experimentally possible to measure the transfer strength to specific final states with high efficiency. In reactions with heavy ions, one can populate states of high angular momentum and, at the same, one can probe the population of specific nuclear levels via transfer of multiple pairs. Valuable information about the structure of those states can be then derived from the study of their decay modes. In the present paper aspects of these studies will be presented, focusing more closely on the reaction mechanism, in particular on the properties of quasi-elastic and deep-inelastic processes and on nucleon–nucleon correlations at energies far below the Coulomb barrier. We concentrated on (near) closed shell systems as they allow a better quantitative comparison between experiment and theory.

abstract

The CLARA-PRISMA setup, composed of an array of 25 Clover detectors placed at the target position of the magnetic spectrometer PRISMA, has recently concluded its campaign to study the structure of moderately neutron-rich nuclei. In this contribution, results obtained in the vicinity of the doubly-magic nucleus \(^{48}\)Ca are presented, together with results obtained for the heavy iron isotopes. The perspectives offered by the forthcoming operation of the AGATA Demonstrator Array coupled to PRISMA are also discussed.

abstract

We have studied energy levels in \(^{63}\)Fe populated in the \(\beta \)-decay of \(^{63}\)Mn. A new (preliminary) level scheme of \(^{63}\)Fe includes 10 excited states connected by 21 \(\gamma \)-rays. The first excited states at 357 and 451 keV have the level half-lives of 110 ps and 780 ps, respectively. Three states, at 357, 451, and 1132 keV, are strongly \(\beta \)-fed with \(\log \,ft \sim 5\), while there is only a very week \(\beta \)-feeding, if any at all, to the ground state. The new results imply that \(^{63}\)Fe departs from a simple shell model structure observed for heavier \(N=37\) isotones of \(^{65}\)Ni and \(^{67}\)Zn.

abstract

The \(\beta \)-decay and isomeric properties of \(^{54}\)Sc, \(^{50}\)K and \(^{53}\)Ca are presented, and their implications with respect to the goodness of the \(N=32\) sub-shell closure discussed.

abstract

The lifetimes of the first excited states of the \(N=30\) isotones \(^{50}\)Ca and \(^{51}\)Sc and the \(Z=18\) isotopes \(^{44-46}\)Ar isotopes have been determined using a novel technique that combines the Recoil Distance Doppler Shift method with the CLARA-PRISMA spectrometers in multinucleon transfer reactions. The results allow determinination of the effective charges above \(^{48}\)Ca and test the strength of the \(N=28\) magic number when moving away from the stability line.

abstract

We present results from two recent runs which illustrate the performance of the PRISMA spectrometer in the proximity of the upper limit of its operational interval, namely \(^{96}{\rm Zr}+^{124}\)Sn at \(E_{\rm lab}=500\) MeV and \(^{136}{\rm Xe}+^{208}\)Pb at \(E_{\rm lab}=930\) MeV. In the latter run, the \(\gamma \) array CLARA also allowed us to identify previously unknown \(\gamma \) transitions in the nuclides \(^{136}\)Cs and \(^{134}\)I.

abstract

Understanding the development of configuration mixing, coherence, collectivity, and deformation in nuclei is one of the crucial challenges in nuclear structure physics, and one which has become all the more important with the advent of next generation facilities for the study of exotic nuclei. We will discuss recent work on phase/shape transitional behavior in nuclei, and the role of changes in sub-shell structure in mediating such transitional regions. We will also discuss a newly found, much deeper, link between nuclear structure and nuclear binding energies.

abstract

It is shown that the Mallmann’s energy correlations, introduced a long time ago for the ground state bands of the even–even nuclei are, in fact, universal. Various bands in all collective nuclei (even–even, odd–even, and odd–odd) obey the same systematics. This unique, universal behaviour indicates the same spin dependence of the energy of the levels in all bands in all collective nuclei. Based on a second-order anharmonic vibrator description, parameter-free recurrence relations between energy ratios are deduced. These relations can be used to predict levels of higher spins in various bands.

abstract

The \(N \sim 90\) region of the nuclear chart has featured prominently as the spectroscopy of nuclei at extreme spin has progressed. This talk will present recent discoveries from investigations of high spin behavior in the \(N \sim 90\) Er, Tm and Yb nuclei utilizing the Gammasphere gamma-ray spectrometer. In particular it will include discussion of the beautiful shape evolution and coexistence observed in these nuclei along with the identification of a remarkable new family of band structures. The latter are very weakly populated rotational sequences with high moment of inertia that bypass the classic terminating configurations near spin 40–\(50 \hbar \), marking a return to collectivity that extends discrete \(\gamma \)-ray spectroscopy to well over \(60 \hbar \). Establishing the nature of the yrast states in these nuclei beyond the oblate band-termination states has been a major goal for the past two decades. Cranking calculations suggest that these new structures most likely represent stable triaxial strongly deformed bands that lie in a valley of favored shell energy in deformation and particle-number space.

abstract

Rotational bands in \(^{110,112}\)Ru and \(^{108}\)Mo have been investigated by means of \(\gamma \)–\(\gamma \)–\(\gamma \) and \(\gamma \)–\(\gamma (\theta )\) coincidences of prompt \(\gamma \) rays emitted in the spontaneous fission of \(^{252}\)Cf. New \(\Delta I = 1\) negative parity doublet bands are found. These bands in \(^{110,112}\)Ru and \(^{108}\)Mo have all the properties expected for chiral vibrations. Microscopic calculations that combine the TAC mean-field with random phase approximation support this interpretation.

abstract

A search of the pygmy resonance in \(^{68}\)Ni was made using the virtual photon technique. The experiment was carried out using the radioactive beam \(^{68}\)Ni at 600 \(A\)MeV impinging on a Au target. The \(^{68}\)Ni beam, produced at GSI with fragmentation of \(^{86}\)Kr at 900 \(A\)MeV on a \(^{9}\)Be target, was separated by the Fragment Separator and the gamma-rays produced at the interaction with the Au target were detected with the RISING set-up including also the HECTOR array. The measured gamma-ray spectra show a peak centered at approximately 11 MeV, whose intensity can be explained in term of an enhanced strength of the dipole response function (pygmy resonance). A pygmy structure of this type was also predicted by different models for this unstable neutron rich nucleus.

abstract

In order to search for a rare kind of shape phase transition in hot rotating nuclei, measurements have been performed of high energy gamma rays from the \(^{188}\)Os nucleus at high excitation energy and high spin. In addition, the possibility of observing the Giant Quadrupole Resonance (GQR) built on excited states has been explored. To carry out more detailed measurements, a sum-spin spectrometer was set up in complete \(4\pi \) configuration. Preliminary results on Giant Dipole Resonance (GDR) decay from hot rotating \(^{192}\)Pt nucleus, obtained with the help of this new device, are presented.

abstract

The \(\gamma \)-decay from the warm rotation in the transition region between order and chaos is studied in the superdeformed (SD) nuclei \(^{151}\)Tb and \(^{196}\)Pb, using the EUROBALL IV array. A number of observables, testing the decay dynamics in the SD well, are compared with predictions from a Monte Carlo simulation of the \(\gamma \)-decay based on microscopic calculations of discrete levels and decay probabilities. Agreement with the data is found only assuming an enhancement of the B(E1) strength around 1 MeV by a factor of 10–100, which is consistent with the evidence for octupole vibrations in both mass regions. The work shows the relevance of \(\gamma \)-spectroscopy in the order-to-chaos regime to highlight specific nuclear structure effects.

abstract

The PARIS project is an initiative to develop and build a high-efficiency gamma-calorimeter principally for use at SPIRAL2. It is intended to comprise a double shell of scintillators and use the novel scintillator material LaBr\(_3\)(Ce), which promises a step-change in energy and time resolutions over what is achievable using conventional scintillators. The array could be used in a stand-alone mode, in conjunction with an inner particle detection system, or with high-purity germanium arrays. Its potential physics opportunities as well as initial designs and simulations will be discussed.

abstract

Investigations on the influence of the neutron enrichment on the decay channels of excited nuclei are presented. Characteristics of fragments with charge \(6 \le Z \le 28\) emitted in \(^{78,82}{\rm Kr}+^{40}\)Ca at 5.5 MeV/\(A\) reactions were measured at the GANIL facility. Data are compatible with an emission process from compound nucleus and are discussed in the framework of the transition state model.

abstract

The \(\gamma \)-ray emission due to dynamical dipole oscillations during fusion process was measured for the \(N\) / \(Z\) asymmetric reaction \(^{16}\)O + \(^{116}\)Sn at 8.1 and 15.6 MeV/u. High-energy \(\gamma \)-rays and light charged particles were measured in coincidence with the recoiling residual nuclei. The measured yield of the high-energy \(\gamma \)-rays exceeds that of the thermalized compound nucleus and this extra-yield increases with beam energy. Data are compared with theoretical predictions of a dynamical calculation based on Boltzmann–Nordheim–Vlasov (BNV) model.

abstract

The deep inelastic reaction \(^{48}\)Ca+\(^{64}\)Ni at 6 MeV/\(A\) has been studied using the CLARA–PRISMA setup. Angular distributions for pure elastic scattering and total cross-sections of the most relevant transfer channels have been measured. The experimental results are compared with predictions from a semiclassical model, showing good agreement for the presently analyzed few neutrons transfer channels. The \(\gamma \)-decay of the most intense reaction products has also been studied, giving indications of the population of states with very short lifetimes.

abstract

Dipole strength distributions measured in unstable neutron-rich nuclei in the \(^{132}\)Sn mass region by utilizing relativistic Coulomb excitation of radioactive beams reveal a sizable fraction of “pygmy” strength below the giant dipole resonance. On the grounds of the RQRPA model, a strong linear correlation between the pygmy strength, parameters of the nuclear symmetry energy and the neutron skin thickness has been found. From the experimentally observed low-lying strength, the symmetry energy pressure \(p_0=2.3\pm 0.8\) MeV/fm\(^3\) and neutron skin thicknesses of \(0.23\pm 0.04\) fm in \(^{130}\)Sn and \(0.24\pm 0.04\) fm in \(^{132}\)Sn have been extracted.

abstract

The nuclei \(^{163,164}\)Dy have been investigated by use of the Oslo method on data from the pick-up reaction \((^{3}{\rm He},\alpha )\) and the inelastic scattering \((^3{\rm He},\,^3{\rm He}')\), respectively. The experiment was conducted at the Oslo cyclotron laboratory (OCL). The \(\gamma \)-decay and ejectiles were measured with the CACTUS multidetector array, which consists of 28 NaI \(\gamma \)-detectores and 8 \(\Delta E - E\) Si particle telescopes. Thermodynamic quantities have been extracted within the micro-canonical ensemble theory. The pygmy resonance found around \(3\) MeV in the \(\gamma \)-ray strength function, also referred to as the scissors mode, was studied. The question whether the width of the pygmy resonance is reaction dependent is addressed.

abstract

We present a new phenomenological mean field approach aiming at the calculation of properties of exotic nuclei. This approach combines the microscopic description of the spin-orbit properties in terms of particle densities, but also vector spin-orbit densities, inspired by results obtained within the Skyrme Hartree–Fock formalism, thus including the contribution of the tensor force. At the same time, the new approach preserves the simplicity of the phenomenological Woods–Saxon calculations and, more importantly, the robustness of the latter towards extrapolations in terms of increasing number of particles and/or isospin.

abstract

A novel way of determining the Hamiltonian of the interacting boson model is proposed. The multi-fermion dynamics of surface deformations studied by the mean-field theory, e.g., Skyrme model, can be mapped, in a good approximation, onto a boson system. The method is examined for well-known nuclei, and predictions are presented for unexplored territories of the nuclear chart, namely, Os–W region nuclei with \(A \gtrsim 200\).

abstract

The pairing gap obtained adding the bare nucleon–nucleon potential and the interaction induced from the exchange of collective vibrations is strongly peaked at the nuclear surface. It is possible to mock up the detailed spatial dependence of this field using a contact interaction, with parameters which are quite different from those commonly used in more phenomenological approaches.

abstract

The spectroscopy and structure of excited states of \(N \sim Z\) nuclei in the mass 70–100 region has been investigated using two techniques. In the \(A \sim 70\)–80 region fusion evaporation reactions coupled with the recoil- \(\beta \)-tagging method have been employed at Jyvaskyla to study low-lying states in odd–odd \(N = Z\) nuclei. Results from these and other data for known odd–odd nuclei above mass 60 will be discussed. In the heavier mass 90 region a fragmentation experiment has been performed using the RISING/FRS setup at GSI. This experiment was primarily aimed at searching for spin gap isomers in nuclei around \(A \sim 96\). The objectives of the latter experiment will be discussed.

abstract

A search for in-beam \(\gamma \)-ray transitions in \(^{101}\)Sn, which contains only one neutron outside the \(^{100}\)Sn core, using a novel approach was carried out at the Argonne Tandem-Linac System. \(^{101}\)Sn nuclei were produced using the \(^{46}\)Ti(\(^{58}\)Ni, 3n)\(^{101}\)Sn fusion–evaporation reaction. Beta-delayed protons with energies and decay times consistent with previous \(^{101}\)Sn decay studies were observed at the focal plane of the Fragment Mass Analyzer. In-beam \(\gamma \) rays were detected in the Gammasphere Ge-detector array and were correlated with the \(^{101}\)Sn \(\beta \)-delayed protons using the Recoil-Decay Tagging method. As a result, a \(\gamma \)-ray transition between the single-neutron \(\nu g_{7/2}\) and \(\nu d_{5/2}\) states situated at the Fermi surface was identified. The measured \(\nu g_{7/2}\)–\(\nu d_{5/2}\) energy splitting was compared with predictions corresponding to various mean-field potentials and was used to calculate multi-neutron configurations in light Sn isotopes. Similar approach can be used to study core excitations in \(^{101}\)Sn and other exotic nuclei near \(^{100}\)Sn.

abstract

Neutron-rich \(^{89,91}\)Rb nuclei populated as fission products in heavy-ion reactions have been studied with the Gammasphere array. The previously known level schemes have been extended to higher excitation energies and spins. Spin and parity assignments were based on angular correlation analyses. A value of \(T_{1/2} = 8(2)\) ns was extracted for the isomeric \(g_{9/2}\) state in \(^{89}\)Rb.

abstract

The yrast structure of the neutron-rich nucleus \(^{97}\)Zr has been studied using fission of target-like products in the reaction of a \(^{48}\)Ca beam on a thick \(^{238}\)U target. The level scheme known from the previous studies up to an energy and spin of approx. 4619 keV and 23/2\(^-\), respectively, has been extended by about 3 MeV and a few units of angular momentum. The located structure can be discussed in terms of shell model configurations.

abstract

A new interaction called PSDPFB has been derived in the full \(p\)–\(sd\)–\(pf\) model space allowing one jump with a \(^4\)He core to describe the \(1\hbar \omega \) intruder states in \(sd\) shell nuclei. This new interaction was tested by calculating the evolution of the negative parity states throughout the shell. A low-lying \(0^-\) state in \(^{40}\)Ca is predicted. The interaction was applied to obtain the \(N=18\) and 20 isotones spectra. Results for the isotones \(^{32}\)Si, \(^{34}\)S and \(^{36}\)Ar and those for \(^{34}\)Si, \(^{36}\)S and \(^{38}\)Ar are presented and compared to experiment.

abstract

We report on a \(\gamma \gamma \) coincidence measurement on \(^{88}\)Zr. One point of interest was a potential \(2^+\) mixed-symmetric state. We measured the multipole mixing ratio for the decays of the second and third \(2^+\) states and precisely determined the energies of the \(2^+_3\) and \(0^+_2\) states. In addition, two new levels and seven new \(\gamma \) transitions were observed. The experiment was performed at the FN-Tandem accelerator at the University of Cologne, using the reaction \(^{89}\)Y\((p,2n)^{88}\)Zr at 17 MeV beam energy. The \(\gamma \)-rays were detected with the Horus HPGe array.

abstract

Experimental \(B\)(M1) and \(B\)(E2) values as well as level energy structures of dipole bands in \(^{142}\)Gd and \(^{130,132}\)La are compared with calculations in the framework of SPAC (Shears mechanism with Principal Axis Cranking) model. All observed dipole bands in these nuclei can indeed be considered as magnetic rotational bands with different planar symmetries and remarkable contribution of collectivity.

abstract

Properties of the low-energy electromagnetic dipole states in even–even \(^{154-160}\)Gd isotopes have been studied within rotational, transitional and Galilean invariant Quasiparticle Random Phase approximation (QRPA) method. It has been shown that the main part of spin-1 states, observed at energy \(2 \div 4\) MeV in \(^{154-160}\)Gd may have M1 character and may be interpreted as the main fragments of the scissors mode. The calculations indicate the presence of a few prominent negative parity \(K^{\,\pi } = 1^-\) states in \(2 \div 4\) MeV energy interval in \(^{154-160}\)Gd.

abstract

High spin states in \(^{194}\)Tl, excited through the \(^{181}\)Ta (\(^{18}\)O, 5\(n\))\(^{194}\)Tl heavy-ion fusion evaporation reaction were studied at iThemba LABS using the AFRODITE array, which consisted of 8 clovers and 6 LEPS detectors. The yrast band built on the 8\(^-\) isomeric state has a \(\pi h_{9\,/\,2} \otimes \nu i_{13\,/\,2}^{-1}\) configuration suitable for a chiral system. One of the new bands built on a new 10\(^-\) level has the same parity and similar excitation energy to those of the yrast band. This new band is linked to the yrast band by several transitions and may be a chiral partner to the yrast band.

abstract

The Neutron star properties are calculated with the various interactions such as charge dependent Reid potential (Reid93) as well as Reid68 and \(AV_{18}\) interactions within the lowest order constrained variational method (LOCV). It is shown that at low densities, neutron star masses exhibit a minimum (\(\simeq 0.1M_\odot \)) and a maximum mass between \(1.4 M_{\odot }\) and \(1.9 M_{\odot }\) which is strongly dependent on the equation of state.

abstract

A relativistic nuclear energy density functional is developed, guided by two important features that establish connections with chiral dynamics and the symmetry breaking pattern of low-energy QCD: (i) strong scalar and vector fields related to in-medium changes of QCD vacuum condensates; (ii) the long- and intermediate-range interactions generated by one- and two-pion exchange, derived from in-medium chiral perturbation theory, with explicit inclusion of \({\mit \Delta }(1232)\) excitations. Applications are presented for the description of ground-state properties.

abstract

An experimental observation of proton decay would be a spectacular proof of Grand Unification. Currently, the best constraint on the proton lifetime for the \(p\to e^{+}\pi ^{0}\) decay channel, coming from the SuperKamiokande experiment, reaches \(8\times 10^{33}\) years. To improve the measurement, much bigger detectors should be constructed. Moreover, a better description of the bound-nucleon states and of the propagation of the proton-decay products through nuclear matter have to be developed. In this article special attention is paid to the argon nucleus because a liquid argon detector is a promising candidate for the future large apparatus.

abstract

Measurements on superallowed \(0^+ \rightarrow 0^+\) nuclear beta transitions currently provide the most demanding test of the Conserved Vector Current (CVC) hypothesis and the most precise value for the up-down element, \(V_{ud}\), of the Cabibbo–Kobayashi–Maskawa (CKM) matrix. Both are sensitive probes for physics beyond the Standard Model. Analysis of the experimental results depends on small radiative and isospin-symmetry-breaking corrections, some of which depend on the specific structure of the parent and daughter nuclei involved. These calculated corrections affect the precision of the results, and experiments are currently focused on reducing their uncertainties. Although nuclear structure only contributes to rather small corrections, it plays a crucial role in these fundamental tests.

abstract

Accelerator Mass Spectrometry (AMS) is today the most selective and sensitive analytical techniques stellar-nucleosynthesis for determination of isotopic abundances ranging down to below \(10^{-15}\). The principle and examples of the method are described. We now apply the technique to measurements of nuclear cross sections of stellar-nucleosynthesis reactions leading to long-lived nuclides. Recent measurements and experimental results for the important \(^{62}\)Ni(\(n\),\(\gamma \))\(^{63}\)Ni (\(t_{1/2}=100\) yrs) and \(^{40}\)Ca(\(\alpha \),\(\gamma \))\(^{44}\)Ti (59 yrs) reactions are presented.

abstract

Atomic masses play an important role in nuclear astrophysics. The lack of experimental values for nuclides of interest has triggered a rapid development of new mass measurement devices around the world, including Time-of-Flight (TOF) mass measurements offering an access to the most exotic nuclides. Recently, the TOF-\(B\rho \) technique that includes a position measurement for magnetic rigidity correction has been implemented at the NSCL. An experiment with a similar TOF-\(B\rho \) technique is approved and planned at the next generation radioactive beam facility (RIBF) at RIKEN.

abstract

While recent measurements have substantially improved our understanding of the \(^{18}\)F(\(p,\alpha \))\(^{15}\)O reaction that is important in novae, the production of \(^{18}\)F is still uncertain by more than 2 orders of magnitude, due in large part to the contribution of a resonance located at \(E_{\rm cm}=330\) keV. We developed a new technique to study resonant (\(p,\alpha \)) reactions and employed it to measure properties of the \(E_{\rm cm}=183\) keV resonance in \(^{17}\)O(\(p,\alpha \))\(^{14}\)N which had been previously reported to decrease \(^{18}\)F production in ONeMg novae by as much as a factor of 10. The previous results were confirmed using the new technique and we now propose to use this technique to study the \(^{18}\)F(\(p,\alpha \))\(^{15}\)O reaction.

abstract

The liquid-drop model which, in addition to the traditional terms, contains the first order curvature energy was successfully used for the description of binding energies of all known isotopes as well as the experimentally measured fission-barrier heights. It was shown that this new Lublin–Strasbourg Drop (LSD) described the available data better than other commonly used macroscopic models.

abstract

We present what we call a new theory of nuclear stability enabled by the combination of the realistic nuclear mean-field and the group theory approaches. It allows us to simplify searches for the strong quantum shell effects at nuclear shapes that result from spectral properties deduced from group theory and geometrical symmetries rather than through ‘brute force numerical search’. Illustrations are presented and discussed.

abstract

Theoretical predictions suggest the presence of tetrahedral symmetry as an explanation for the vanishing intra-band E2 transitions at the bottom of the odd-spin negative-parity band in \(^{156}\)Gd. The present study reports on experiment performed to address this phenomenon. It allowed to remove certain ambiguouities related to the intra-band E2 transitions in the negative-parity bands, to determine the new inter-band transitions and reduced probability ratios \(B\)(E2)/\(B\)(E1) and, for the first time, to determine the experimental uncertainties related to the latter observable.

abstract

Large scale calculations based on the microscopic–macroscopic method with Woods–Saxon single particle potential guided by the use of the discrete point group symmetries allow us to find the new islands of nuclear stability. These new stability regions are the consequence of particularly strong shell effects which are obtained in the calculations when the nuclear mean field is allowed to deform by respecting some special symmetries related to the so called high-rank point groups. The underlying mechanism is illustrated together with the full chain of the symmetry-associated magic numbers.

abstract

Within the dinuclear system model we analyse the production of yet unknown superheavy nuclei in actinide-based complete fusion reactions. The yields of superheavies with \(Z\gt 118\) are sensitive to the location of the next proton shell closure beyond \(^{208}\)Pb.

abstract

In the paper we present scintillation-ionization detector (SID) — a new device for support of the superheavy elements (SHE) identification in the standard, complete fusion methods. We highlight problems with background effects in SHE production and their minimization by introducing SID to the detection set-up at GANIL. We also point possible application of this detector in alternative approach for superheavy elements production.

abstract

We investigate the possibility of observing toroidal breakup configurations in Au+Au collisions using the CHIMERA multidetector system. BUU simulations indicate that the threshold energy for toroidal configuration formation is around 23 MeV/nucleon. The simulations of the decay process using the static model code ETNA indicate the sensitivity of some observables to different studied break-up geometries.

abstract

Within the self-consistent constraint Skyrme–Hartree–Fock+BCS model (SHF+BCS), we found equilibrium toroidal nuclear density distributions in the region of super-heavy elements. For nuclei with a sufficient oblate deformation (\(Q_{20} \leq -200\) b), it becomes energetically favourable to change the genus of nuclear surface from 0 to 1, i.e., to switch the shape from a biconcave disc to a torus. The energy of the toroidal (\({\rm genus} = 1\)) SHF+BCS solution relative to the compact (\({\rm genus} = 0\)) ground state energy is strongly dependent both on the atomic number \(Z\) and the mass number \(A\). We discuss the region of \(Z\) and \(A\) where the toroidal SHF+BCS total energy begins to be a global minimum.

abstract

The isotopic dependence of \(K\)-isomer states in heavy nuclei is treated.

abstract

This contribution reviews the recent results of the experiments performed at SHIP in the field of \(K\)-isomer studies, where we aimed at a study of high \(K\)-structures in odd-mass nuclei. In particular the results from the study of multi-quasi-particle isomeric states in \(^{253}\)No and \(^{255}\)Lr will be presented in detail. The high \(K\)-isomer in \(^{253}\)No gives also the possibility to observe a rotational band, which was not observed in previous in-beam studies

abstract

Nuclear spectroscopy using radioactive isotope beams requires dedicated set-ups. At the SIS/FRS facility at GSI exotic beams at relativistic energies were employed for Coulomb excitation and secondary fragmentation experiments with the fast beam RISING set-up. Shell evolution far off stability, \(pn\)-pairing, symmetries and nuclear shapes were studied in nuclei ranging from \(^{36}\)Ca to \(^{136}\)Nd. In another Ge-detector configuration a series of \(g\)-factor experiments was performed. Recently the compact detector arrangement of RISING — providing about 15% full energy efficiency — went into operation. Seniority isomers in medium heavy nuclei at the proton drip line have been investigated as well as new isomers found in neutron rich nuclei, e.g. \(^{204}\)Pt. Most recently the decay properties of \(^{100}\)Sn were investigated successfully. At future FAIR/GSI the Super-FRS facility within the NUSTAR project will provide an enormously enlarged variety of exotic beams. To fully exploit these beams the HISPEC/DESPEC project aims to develop, build and operate optimized experimental set-ups. Based on the experience with RISING novel particle identification and tracking detectors will be employed. For in-beam \(\gamma \) detection AGATA detectors are foreseen as well as a dedicated compact Ge tracking and imaging array for decay experiments. Well before the Super-FRS facility will become operational, detectors developed for HISPEC/DESPEC will be commissioned and employed for experimental campaigns within the PRESPEC project at the FRS facility at GSI.

abstract

Progress in the measurement of the ground state magnetic moments of mirror nuclei at NSCL is presented. The systematic trend of the spin expectation value \(\langle s\rangle \) and the linear behavior of \(\gamma _p\) versus \(\gamma _n\), both extracted from the magnetic moments of mirror partners, are updated to include all available data.

abstract

The current status and outlook for the Doppler-effect based lifetime measurements program at the National Superconducting Cyclotron Laboratory is presented, including the impact of the Digital Data Acquisition System which provides gamma-ray tracking capabilities for the Segmented Germanium Array.

abstract

Gamma-ray spectroscopy using intermediate-energy RI beams of projectile fragments has been useful for investigating low-lying states of extremely neutron rich nuclei far from the valley of stability. Coulomb excitation and proton inelastic scatterings are probing reactions most favorably employed, and problems of appearance/disappearance of magicity and emergence of new regions of deformation have been the central research objectives. In this paper, we first present a review on the novel features of the spectroscopic methods with RI beams, and then describe some of the highlights of such spectroscopic works recently performed at RIKEN.

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The SPIRAL2 project, an important extension of the GANIL facility and one of the ESFRI list European research infrastructures entered recently in the construction phase. In the following, a physics case of the facility based on a use of high intensity stable and radioactive beams is presented. Expected performances and main technical parameters of the facility as well as planned new experimental areas and detectors are introduced.

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SPES (Selective Production of Exotic Species) is an INFN project to develop a Radioactive Ion Beam (RIB) facility as an intermediate step toward EURISOL. The key feature of SPES is to provide high intensity and high-quality beams of neutron rich nuclei to perform forefront research in nuclear structure, reaction dynamics and interdisciplinary fields like medical, biological and material sciences. The exotic isotopes will be reaccelerated by the ALPI Superconducting Linac at energies of 11 \(A\)MeV for masses in the region of \(A=130\) amu with an expected rate on target of 10\(^9\) pps. This represent a substantial improvement to the actual available ISOL facilities both from the point of view of intensity and energy of the exotic beam.

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An extended work is in progress concerning the target development for the SPES (Selective Production of Exotic Species) project. The SPES will be an ISOL based facility (Isotope Separation On Line) in which a proton beam of 40 MeV and 0.2 mA impinges directly on a uranium carbide target. After the mass separation and re-acceleration on the experimental sites, the RIBs will have an intensity of the order of 10\(^{9}\) pps (for \(^{132}\)Sn) and an energy up to 13 MeV/\(u\). The new idea that characterize this project is the design of its target: we propose a target configuration capable to keep high the number of fissions, low the power deposition and fast the release of the produced isotopes.

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Commissioned in 1994, the Warsaw Cyclotron is operated by the Heavy Ion Laboratory of the University of Warsaw as a “User Facility” with around 100 national and foreign users per year. The isochronous \(K_{\,\rm max}=160\) machine currently delivers around 3000 h of heavy ion beams per year, ranging from B to Ar, with energies between 2 and 10 MeV/nucleon. The current research programme comprises nuclear physics, atomic physics, materials science, solid state physics, biology, particle detector development and testing. In this article the experimental stations placed on the beam-lines of the cyclotron and some recent nuclear physics experiments are presented.

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The transfer probabilities for \(^{20}\)Ne + \(^{90}\)Zr and \(^{20}\)Ne + \(^{92}\)Zr at energies near the Coulomb barrier were measured. This quantity turned out to be very similar for both Zr isotopes and does not explain the observed differences in the barrier height distributions for these systems.

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In Coulex experiments at intermediate beam energies besides electromagnetic forces the nuclear interaction may occur. These two excitation mechanisms result in emission of \(\gamma \)-rays with a characteristic angular distribution \(W(\theta )\). Measurement of \(W(\theta )\) was performed at the RISING fast beam set-up to probe the electromagnetic-nuclear interface. Unexpectedly large hadronic-like contribution was observed when high \(Z\) projectiles were used.

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One-neutron knockout reactions have been studied in a systematic way for a set of neutron-rich projectiles. The goal of the experiment, performed at GSI, was to explore the evolution of the nuclear structure close to the neutron drip line, in the region between C and Al. The momentum distributions of the surviving fragments and the cross-sections of the knockout process have been measured and used as physical observables. This report focuses on oxygen and nitrogen isotopes around \(N=14\). In particular, we discuss the case of \(^{22}\)N, for which the mentioned observables have been determined for the first time. We will consider \(^{23}\)O, already studied in earlier experiments, as a reference.

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The fragmentation of neutron-rich Sn isotopes obtained from the fission of \(^{238}\)U projectiles at 950 MeV/\(u\) has been investigated at the FRagment Separator (FRS) at GSI. In order to study the feasibility of a two-step reaction scheme for the production of medium-mass neutron-rich nuclei, fragments with masses \(A \approx 130\) have been isotopically resolved in the first part of FRS and their fragmentation residues identified in the second part.

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Relativistic projectile fragmentation of a \(^{208}\)Pb primary beam has been used to produce neutron-rich nuclei with proton-holes relative to the \(Z = 82\) shell closure, i.e. , “south” of Pb. \(\beta \)-delayed \(\gamma \)-ray spectroscopy allows to investigate the structural properties of such nuclei with \(A \sim 195 \rightarrow 205\). The current work presents transitions de-exciting excited states in \(^{204}\)Au, which are the first spectroscopic information on this \(N = 125\) isotone.

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The nuclear structure of neutron-rich \(N \gt 126\) nuclei has been investigated following their production via relativistic projectile fragmentation of a \(E\) / \(A=1\) GeV \(^{238}\)U beam on a Be target. The preliminary analysis indicates the presence of previously unreported isomeric states in the \(N=128\) isotones \(^{208}\)Hg and \(^{209}\)Tl.

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Decays of neutron-rich \(A\sim 190\) nuclei have been studied following projectile fragmentation of a \(^{208}\)Pb beam on a \(^{9}\)Be target at the GSI Fragment Separator. Gamma-ray decays from previously reported isomeric states in \(^{188}\)Ta, \(^{190}\)W and \(^{192,193}\)Re were used as internal calibrations for the particle identification analysis, together with the identification of previously unreported isomeric decays in \(^{189}\)Ta and \(^{191}\)W. The current work also identifies \(\beta \)-delayed \(\gamma \) rays following the decay of \(^{188}\)Ta to \(^{188}\)W for the first time.

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Isomeric states in nuclei with \(Z=62\)–67 and \(A=142\)–152 produced in the fragmentation of the relativistic (1 GeV/nucleon) \(^{208}\)Pb beam were investigated. Isomeric ratios were determined for 10 isomeric states. Significant differences between theoretical and experimental values were observed.

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Gamma rays from the decay of an isomer in \(^{190} W_{116}\) have been observed following projectile fragmentation of a 1 GeV per nucleon \(^{208}\)Pb beam. An earlier experiment indicated decay from a (10\(^-\)) isomer to the ground state rotational band. Improved statistics have enabled gamma coincidence and time-difference measurements to be made which alter the previous interpretation. Blocked BCS calculations have also been used together with reduced hindrance factors to indicate possible values of spin-parity for the isomer.

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Neutron-deficient nuclei with \(N=126\) have been populated following projectile fragmentation of a \(^{238}\)U beam with energy 1 GeV/\(A\). The decay of several previously reported isomers has been measured. This will allow us to calculate high-spin isomeric ratios and compare them with model calculations to allow a better understanding of the reaction mechanism.

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The indirect method of the light exotic nuclei study in the experiments with the stable ion beams produced in many-nucleon-transfer reactions is presented. The data of elastic and inelastic scattering as well as of transfer reactions were analysed with the optical model (OM) and coupled-reaction-channels method (CRC). The potential parameters for the entrance reaction channel must be deduced from the analysis of the elastic and inelastic scattering data before the CRC-calculation of reaction cross-section. The results for the \(^{12}\)C(\(^{11}\)B, \(^{15}\)N)\(^8\)Be reaction are presented as an example. The energy dependence of optical potential parameters for this reaction are also presented.

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Missing mass spectra for \(^8\)He and \(^{10}\)He obtained in the reactions \(^3{\rm H}(^6{\rm He},\, p)^8\)He and \({}^3{\rm H}(^8{\rm He},\, p)^{10}\)He, respectively, are presented.

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Electron screening of the Coulomb barrier between reacting nuclei leads to an exponential-like enhancement of nuclear cross sections for lowering projectile energies. Recently, this effect has been demonstrated by many groups for the \(^2\)H(\(d,\,p\))\(^3\)H and \(^2\)H(\(d,\,n\))\(^3\)He reactions taking place in metallic environments. The experimental results show a much stronger effect for metals than for gaseous or insulator targets. Similar effects are also expected for radioactive alpha decays. Based on experimental and theoretical results achieved for nuclear reactions and a dynamic approach to the electron screening in the electron gas, an increase of alpha-decay constants of order of a few per cent is anticipated for metallic environments.