abstract

New developments in nuclear spectroscopy of prompt emission at the target and decay emission at the focal plane of recoil separators are described here. In-beam \(\gamma \)-ray measurements of even–even nuclei in the rotational superheavy region, \(^{252,254}\)No, have been carried out. These measurements have revealed the properties of the ground state rotational bands. Attempts to measure the properties of odd mass nuclei await the further development of conversion electron spectroscopy, and early results from the SACRED spectrometer used in conjunction with the recoil separator RITU are given here. The future development of sensitive focal plane instruments, to identify decay processes following the radioactive decay of the parent nucleus is also described.

abstract

Problem of production of even–even superheavy nuclei in their first excited state 2+ is discussed. Measurement of energy of this state is considered as a way to learn if these nuclei are deformed. Superheavy nuclei situated around the nucleus \(^{270}\)Hs, which according to calculations are expected to be deformed, are studied. Particular attention is given to calculations of the branching ratio \(p_{2+}\)/\(p_{0+}\) between \(\alpha \) decay of a nucleus to the 2+ state and to the ground state 0+ of its daughter. Sensitivity of this ratio to various factors appearing in the calculations is discussed.

abstract

The JYFL gas-filled recoil separator RITU, combined with Ge detector arrays, has successfully been employed in Recoil-Decay-Tagging (RDT) experiments in order to probe, for the first time, structures of several very neutron deficient heavy nuclei. In this contribution new data for light even-mass Hg, Pb and Po nuclei are shown and discussed.

abstract

Excited states in the second minimum of \(^{240}\)Pu were populated by the \(^{238}\)U(\(\alpha ,2n\)) reaction at \(E_\alpha \)=25 MeV. Conversion electrons from electromagnetic transitions preceding the fission of the 3.7 ns \(^{240f}\)Pu shape isomer have been measured. In a combined analysis of e\(^-\) and high resolution \(\gamma \)-ray spectroscopy data previously established octupole bands could be studied in more detail. In order to study higher lying states in the second and third minimum the \(^{239}\)Pu\((d,pf)^{240}\)Pu, and the \(^{233}\)U\((d,pf)^{234}\)U reactions have been studied with high energy resolution. The observed fission resonances were described as members of rotational bands with rotational parameters characteristic to super- and hyperdeformed nuclear shapes. The level density of the most strongly excited states has been compared to the prediction of the back-shifted Fermi-gas formula and the energy of the ground state in third minimum has been estimated for the first time in \(^{234}\)U. The fission fragment mass distribution of the hyperdeformed states in \(^{236}\)U has also been measured. The width of the mass distribution, coincident with the hyperdeformed bands, is significantly smaller than the ones obtained in coincidence with background regions below and above the resonances, which suggests a pear-shaped di-nuclear configuration of \(^{236}\)U in the third well of the potential barrier.

abstract

The structure of SuperHeavy Nuclei (SHN) is analyzed in two microscopic approaches. First one is the Hartree–Fock–Bogolyubov method used with the Gogny force, applied to a large range of nuclei with axial and left–right symmetries. The second one breaks both of these symmetries in mean field. Potential energy surfaces of a few transactinides are studied in this framework. One observes that the fission paths can be strongly modified, leading to significant changes in lifetimes obtained from HFB-D1S.

abstract

The effect of magnetic field reversal on transmission of the Mössbauer radiation through a crystal as well as on the reaction yield is analyzed. The enhancement of coherent radiative channel as well as suppression of incoherent scattering and reactions caused by the field reversal, are discussed.

abstract

The quadrupole excitations of transuranic nuclei are described dynamically in the frame of the microscopic collective Bohr Hamiltonian modified by adding the coupling with the pairing vibrations. The ground-state bands in No and Fm even–even isotopes are reproduced within the model containing no adjustable parameters.

abstract

The effective chiral mean-field model of Furnstahl, Serot and Tang (FST) is proposed to examine stability of superheavy nuclei. The FST model is an example of a nuclear effective field theory where the hadronic Lagrangian is constructed according to the symmetries of quantum chromodynamics and the “naturalness” condition.

abstract

Ground-state properties of heaviest nuclei are recalculated within a macroscopic–microscopic approach. Both macroscopic and microscopic parts of energy are modified. Such properties as deformation, masses, neutron separation energies, \(\alpha \)-decay energies and half-lives are studied. A large region of even–even nuclei with proton, \(Z\)=82–128, and neutron, \(N\)=126–188, numbers is considered.

abstract

The intermediate structure of the fission resonances has been observed in \(^{240}\)Pu. A resonance structure found around the excitation energy of 4.5 MeV was interpreted as a group of \(K^\pi =0^+\) superdeformed rotational bands. The moments of inertia and level density distributions were also deduced for the individually observed band-heads.

abstract

An overview of recent high-spin nuclear structure studies in proton-rich nuclides near the doubly-magic isotope \(^{56}\)Ni is presented.

abstract

A review of some results we have recently obtained for medium-light nuclei is reported, with particular stress on the nuclear properties we have studied and what we have learned from these experiments. To illustrate these features of \(f_{7/2}\)-shell nuclei, we present some examples on rotational bands in even–even and odd–odd nuclei, backbending and band termination phenomena, intruder bands and shape coexistence and, finally, analogue bands in \(T = 1\) mirror nuclei.

abstract

New experimental data on very neutron-deficient Kr isotopes extend the systematic of low-lying 0\(^+\) states in this mass region. Clear evidence for shape isomers was found in \(^{74}\)Kr and in the \(N=Z\) nucleus \(^{72}\)Kr. Coulomb excitation in inverse reaction kinematics was shown to be powerful method in order to disentangle the different shapes of atomic nuclei.

abstract

Nuclear structure of the doubly magic \(^{68}\)Ni and its neighbors has been studied by spectroscopic techniques. Developing a new instrument isomer-scope, we have measured \(\gamma \) rays from nano-second isomers produced in heavy-ion deep-inelastic collisions with great sensitivity.

abstract

New high spin excitations in several light \(f_{7/2}\) nuclei have been studied by means of EUROBALL IV. The application of the Recoil Filter Detector has allowed for a significant reduction of the Doppler broadening of measured high energy \(\gamma \)-lines. In the article, a band termination observed for the intruder rotational bands in \(^{45}\)Sc is discussed. Results are compared with shell model calculations.

abstract

The odd rank analyzing powers \(^TT_{10}\) and \(^TT_{30}\) for \(^{12}\)C(\(^7\vec {\rm Li},^7\)Li)\(^{12}\)C and \(^{12}\)C(\(^7\vec {\rm Li},\alpha \))\(^{15}\)N have been measured with high precision for a \(^7\vec {\rm Li}\) bombarding energy of 34 MeV. The angular distributions of the \(^TT_{10}\) and \(^TT_{30}\) data are strongly correlated, marking the first experimental evidence of a relationship between analyzing powers of different rank. The ratio of \(^TT_{30}\) to \(^TT_{10}\) obeys limits derived from the assumptions that the reaction is both peripheral and well localized in the reaction plane, allowing, for the first time, a third rank analyzing power to contribute to our understanding of \(^7\)Li.

abstract

A projectile fragmentation experiment has been performed to populate the neutron-rich \(A\sim \)190 mass region, approaching the \(Z=82\), \(N=126\) closed shell. A previously unreported isomer is found in \(^{200}\)Pt, being the first new example, from fragmentation reactions, of a seniority 4 state established from \(\gamma \)–\(\gamma \) coincidences.

abstract

The induced pairing interaction arising from the exchange of low-lying collective surface vibrations among nucleons moving in time reversal state close to the Fermi energy is found to lead to values of the pairing gap which constitute a large fraction of those experimentally observed.

abstract

Characteristics of the segmented Super Clover germanium detector response in close geometries have been studied. Results obtained with localising hit pattern recognition are compared with results from add-back and individual crystal analysis. The detector has been used at the focal plane of a gas filled recoil separator to detect isomeric gamma-rays from the nuclei produced in the \(^{150}\)Sm(\(^{42}\)Ca,4n)\(^{188}\)Pb reaction. Coincidence data from the detector was analysed and the level scheme below the 1.2 \(\mu \)s isomeric state in \(^{188}\)Pb could be deduced.

abstract

The nucleus \(^{94}\)Mo was investigated using a powerful combination of a photon scattering experiment, an off-beam \(\gamma \gamma \) coincidence study following the \(\beta ^+\) decay of \(^{94m}\)Tc, and the fusion-evaporation reaction \(^{91}\)Zr(\(\alpha ,n)^{94}\)Mo. We identified the one-phonon \(2^+\) Mixed-Symmetry (MS) state and two-phonon MS states in the nucleus \(^{94}\)Mo from the measurement of absolute M1 and E2 transition strengths. These strengths were determined from photon scattering cross sections, Doppler shifts, branching ratios, and E2/M1 mixing ratios. The experimental results are in reasonable agreement with the interacting boson model.

abstract

The optimal parameters of the Nilsson single particle potential in order to reproduce the experimental radii of the ground states of nuclei and the \(K\)-isomers Lu, Hf, Ta were found. The isospin dependence of harmonic oscillator frequency and the new parameters set of the Seo correction term in the single-particle potential make able to use the macroscopic–microscopic model with free quasiparticle BCS pairing approximation to describe the properties of nuclear ground and rotational \(K\)-isomeric states.

abstract

This work is devoted to the Coulomb excitation of \(^{165}\)Ho. Experiments were performed at the Heavy Ion Laboratory of Warsaw University. A model-independent analysis using the GOSIA code yielded a set of reduced matrix elements values coupling the low-lying collective excited states. A quadrupole sum rules approach was used to determine the deformation of the states. A remarkable change of quadrupole moment in one of the \(\gamma \)-vibrational bands was found.

abstract

Results from a number of GDR experiments aiming at the investigation of hot nuclear shapes in two very different mass regions and performed with the HECTOR array are presented. For \(A\!=\!46\) Jacobi shapes at high angular momenta were observed. For \(A\!=\!216\) indications of large deformations at angular momenta close to the fission limit were found.

abstract

High-energy gamma rays in coincidence with low-energy discrete transitions have been measured by coupling EUROBALL with the HECTOR array. The high-energy \(\gamma \)-ray spectrum in coincidence with superdeformed (SD) discrete transitions of \(^{143}\)Eu shows an ‘excess’ between 9-12 MeV if compared with the one associated to cascades which do not pass through the SD configurations. Such an ‘excess’ is in the energy region where one expects the low energy component of the GDR strength function built on a SD state. High energy \(\gamma \)-rays have been found also to enhance the population of the discrete SD band, the ridge structure and the superdeformed quasi-continuum showing that the E1 cooling is a preferred way to feed SD configurations.

abstract

Photon angular distributions and energy spectra up to the kinematic limit have been measured in 190 MeV proton reactions with light and heavy targets. For the first time photon spectra in dependence of scattered protons have been measured to investigate the influence of the multiple-scattering process on the photon production. Based on predictions for the free \(pn\) bremsstrahlung amplitude a strong suppression of bremsstrahlung relative to a quasi-free production model is observed in the low-energy regime of the photon spectrum in \(p\)+nucleus reactions. We attribute this effect partly to modifications of the bremsstrahlung amplitude in the nuclear medium and partly to interference of photon amplitudes due to multiple scattering of nucleons.

abstract

High-energy \(\gamma \)-ray spectra and angular distributions from \(^{12}\)C+\(^{24,26}\)Mg, \(^{12}\)C+\(^{58,64}\)Ni and \(^{18}\)O+\(^{100}\)Mo reactions at few bombarding energies, between 5 and 11 MeV/u, were measured and analyzed by taking into account complete and incomplete fusion processes and bremsstrahlung emission. The GDR parameters were extracted as a function of the average excitation energy and the bremsstrahlung parameters as a function of \((E_{proj}-V_c)\)/\(A\).

abstract

The \(^{18}\)O + \(^{27}\)Al reaction at 8.3 MeV\(/u\) is discussed in comparison with the same reaction performed for lower projectile energies between 2.5 and 6 MeV\(/u\). In this report an influence of additional reaction mechanism — an incomplete fusion — has been analyzed.

abstract

We investigate the collisional damping of giant dipole resonance at finite temperature in the basis of a non-Markovian transport approach. We perform our calculations in Thomas–Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Gogny force. The results account for about 30\(\%\) of the observed widths in \(^{120}\)Sn and \(^{208}\)Pb at finite temperatures.

abstract

The formation of an excited rotating deformed nucleus and its subsequent decay through the fission process, or ending up as an evaporation residue, is studied taking into account particle evaporation. Several nuclei ranging from \(^{126}\)Ba to some super-heavy elements are investigated. Until recently, we have only considered average pre-fission multiplicities, as these were the experimental available data. A newly developed analysis of experimental data can now give access to pre-fission multiplicity distributions. A first comparison between theoretical and experimental particle-multiplicity distributions is given.

abstract

The performances of the composite Cluster detectors of the EUROBALL array have been investigated with \(\gamma \)-rays of 15.1 MeV produced in the reaction \(^{11}{\rm B} + {\rm D} \to ^{12}{\rm C} + \gamma + n\) at 19.1 MeV. The Cluster detector is made of 7 encapsulated germanium crystals mounted in a single cryostat. The pulse height to energy conversion of the individual crystals is found to be very linear. The coincidence fold distribution is given for various energies and compared to simulation calculations of the Cluster response. A simple add-back procedure improves consistently the full energy peak efficiency. The efficiency of the composite detector is compared to that of large volume BaF\(_2\) scintillator.

abstract

The level densities and \(\gamma \)-strength functions of the almost spherical \(^{148}\)Sm and \(^{149}\)Sm nuclei have been extracted. The temperature curve, derived within the framework of the micro canonical ensemble, shows structures, which we associate with the break up of Cooper pairs. The nuclear heat capacity is deduced within the framework of the canonical ensemble and exhibits an S-shape as a function of temperature indicating a phase transition. The results are compared to the results for well deformed \(^{161,162}\)Dy and \(^{171,172}\)Yb isotopes.

abstract

The Coulomb excitation experiment on the \(^{178}\)Hf was performed using 650 MeV beam of \(^{136}\)Xe. The first observation of discrete transitions in the \(K^{\pi }=8^{-}\) isomeric band, Coulomb excited from \(K^{\pi }=0^{+}\) ground state, is reported. The possible mechanisms of E1 coupling of the ground state band and the isomeric band is discussed.

abstract

\(5/2^{+}[402]\) 10.8 ns isomeric level at 482 keV in \(^{\rm 181}\)Ta was Coulomb-excited by 225 MeV \(^{\rm 58}\)Ni, starting from \(7/2^{+}[404]\) ground state. Particle–\(\gamma \) and particle–\(\gamma \)–\(\gamma \) events were collected. Excitation through newly observed gamma-vibrational \(K^{\pi }=3/2^{+}\) band turned out to be 50 times more efficient than direct excitation.

abstract

The present paper is comprised of two parts. First, we give a brief survey of the theoretical framework for microscopic nuclear structure calculations starting from a free nucleon–nucleon potential. Then, we present some selected results of a comprehensive study of nuclei near doubly closed shells. In all these shell-model calculations we have made use of realistic effective interactions derived from the Bonn-A nucleon–nucleon potential by means of a \(G\)-matrix folded-diagram method. We show that this kind of calculation yields a very good agreement with experiment for all the nuclei considered. This leads to the conclusion that realistic effective interactions are now able to describe with quantitative accuracy the properties of complex nuclei.

abstract

A summary of recent experimental efforts on nuclei in very close vicinity to the doubly magic \(^{132}\)Sn and perspectives for further progress in the very near future, are presented. A special attention is given to the selected key developments in this mass region via three avenues of production and investigation of exotic nuclei: \(\beta \) decay at the ISOL facilities, prompt \(\gamma \)-rays in spontaneous fission probed using large Ge arrays, and \(\mu \)-second isomers produced in the fragmentation and in-flight separation of energetic uranium beams or in fission using recoil separators.

abstract

The shell model residual interaction around \(^{208}\)Pb is studied. Matrix elements of a realistic interaction, calculated from the interaction between free nucleons, are compared with experiment. The calculated interaction has been improved by adjustments to experimental data, to better describe nuclei around \(^{208}\)Pb. Some systematic trends of the differences between calculated and empirical interaction have been found. Specifically, the interaction between particles and holes in \(^{208}\)Pb is treated and that between two proton holes, based on new data for \(^{206}\)Hg.

abstract

We investigate the nature of the low-lying spectra of many-body systems with random two-body interactions. Our study shows that the higher \(J\)-ground states are more orderly and develop the larger energy gaps than the ones in the \(J=0\)-sector.

abstract

In the PS209 experiments at CERN two kinds of measurements were performed: the in-beam measurement of X-rays from antiprotonic atoms and the radiochemical, off-line determination of the yield of annihilation products with mass number \(A_{\rm t} -1\) (less by 1 than the target mass). Both methods give observables which allows to study the peripheral matter density composition and distribution. A comparisons of the PS209 results with the theoretical and semiempirical predictions for neutron and proton densities and with the differences \(\Delta r_{np}\) of the rms radii of neutrons and protons obtained in other experiments are also presented.

abstract

The size and shape of the neutron and proton density distributions obtained in the Hartree–Fock–Bogoliubov (HFB) calculations with the Gogny force D1S are investigated. The radial density distributions at distances far from nuclear surface are analyzed. Significant differences in the multipole deformations of neutron and proton densities along the fission paths are found. The effect of an additional constraint imposing the same size and deformation of neutrons and protons distributions on barrier heights is studied.

abstract

High spin structures were studied in the \(^{105}\)Rh and \(^{136}\)La nuclei using the \(^{100}\)Mo(\(^{11}\)B,\(\alpha 2n){}^{105}\)Rh and \(^{128}\)Te(\(^{11}{\rm B},xn)^{136}\)La reactions respectively. DCO ratios, \(\alpha \)–\(\gamma \)–\(\gamma \) and \(\gamma \)–\(\gamma \) coincidences were measured. Four new bands were identified in \(^{105}\)Rh and three in \(^{136}\)La. The results were interpreted with the CSM.

abstract

Two nuclear systems near and beyond the proton drip line are examined following spectroscopy with Gammasphere coupled to the Fragment Mass Analyzer. The proton-rich \(N=84,85\) isotones are found to have an yrast structure dominated by \(\nu h_{9/2}\) configurations. In \(^{173}\)Au the first evidence is seen for the limit of energy which a nucleus beyond the proton drip line can sustain.

abstract

Energy loss of 6 MeV/\(u\) \(^{56}\)Fe ions in a partially ionized helium plasma has been for the first time measured as a function of incident charge state ranging from 21+ to 25+. Enhancement of the energy loss of the ions in the discharge plasma has been observed over that in cold helium gas. The enhanced stopping of \(^{16}\)O ions with energies of \(\sim \) 0.2 MeV/\(u\) in laser ablated LiH plasma has been also observed over that in cold matter. Theoretical calculation proposed by Sigmund reproduces the energy dependence of the experimental stopping power of the \(^{16}\)O ions in the plasma.

abstract

Stable octupole deformation was predicted and subsequently found to occur centered around the reinforcing shell gaps at \(Z=56\) and \(N=88\) for \(\beta _3 \simeq 0.15\). Evidence for stable octupole deformation is reviewed. New results in \(^{145}\)Ba and \(^{141}\)Ba are presented. Rotational enhancement of octupole deformation is found at intermittent spins in Ba and La nuclei and the quenching of such deformation at higher spins in \(^{146}\)Ba but not in \(^{144}\)Ba. Symmetric and asymmetric shapes coexist in \(^{145}\)Ba and \(^{145}\)La. Evidence for octupole correlation is found in \(^{147}\)Pr but only \(h_{11/2}\) bands are found in \(^{149,151}\)Pr. The new \(^{141}\)Ba levels have two sets of two intertwined bands of levels with the characteristics of octupole deformation as found in \(^{143,145}\)Ba, however, a problem occurs with the assignment of parities in \(^{141}\)Ba.

abstract

Recent proton radioactivity studies at the Holifield Radioactive Ion Beam Facility at Oak Ridge are presented. The experiments were performed by means of a Recoil Mass Separator (RMS) and digital processing of its detector signals. Observation of fine structure in proton emission from the activities : \(^{145}\)Tm (\(T_{1/2}\approx 3\,\mu \)s) and \(^{146m,gs}\)Tm (\(T_{1/2}\approx 200\) ms and 100 ms, respectively) is reported. The structure of the proton emitting states is analyzed in terms of a spherical approach. The properties of daughter states, a 2\(^{+}\) state in \(^{144}\)Er and the \(s_{1/2}\) and \(h_{11/2}\) neutron levels in \(^{145}\)Er, are deduced.

abstract

The IGISOL facility at the Department of Physics of the University of Jyväskylä (JYFL) is delivering radioactive beams of short-lived exotic nuclei, in particular the neutron-rich isotopes from the fission reaction. These nuclei are studied with the nuclear spectroscopy methods. In order to substantially increase the quality and sensitivity of such studies the beam should undergo beam handling: cooling, bunching and isobaric purification. The first two processes are performed with the use of an RFQ cooler/buncher. The isobaric purification will be made by a Penning trap placed after the RF-cooler element. This contribution describes the current status of the ion trap project and its future prospects. The latter comprise the precise nuclear mass measurements, nuclear spectroscopy in the Penning trap interior as well as the laser spectroscopy on the extracted beams.

abstract

The recently reconstructed focal plane detector system for the gas-filled recoil separator RITU was used to observe a new proton emitter \(^{164}\)Ir. The nuclide was produced via the \(p5n\) fusion evaporation channel using a \(^{64}\)Zn beam on a \(^{106}\)Cd target. The proton energy \(E_{p} = 1817(9)\) keV and half-life \(T_{1/2} = 113^{+62}_{-30}\) \({\mu }s\) were used to characterize the decaying state to be \([{\pi }h_{11/2}{\nu }f_{7/2}]9^{+}\). The new focal plane detector system and the results of the proton decay studies will be discussed.

abstract

Results of a measurement of relative yields and \(\gamma \)-ray multiplicities for nuclei populated in a heavy ion induced fusion–evaporation reaction in the region of \(^{100}\textrm {Sn}\) are presented. The relative cross sections for about 20 reaction products were derived from the intensities of \(\gamma \) rays feeding ground states of respective nuclei, whereas the \(\gamma \)-ray multiplicities were determined by using 30 BaF\(_{2}\) detectors surrounding the target.

abstract

Excited states of nuclei in the vicinity of \(^{100}\)Sn have been studied using the EUROBALL detector array. Gamma-ray lines from \(^{103}\)Sn have been identified for the first time, and a level scheme of low-lying excited states of \(^{103}\)Sn has been established. New constraints on energies of single particle orbitals with respect to the \(^{100}\)Sn core are obtained.

abstract

The isomeric structure of the \(N=77\) isotones \(_{\;\:65}^{142}\)Tb and \(_{\;\:67}^{144}\)Ho have been studied with the \(^{92}\)Mo(\(^{54}\)Fe, \(xpn\)) fusion evaporation reaction at the University of Jyväskylä. The Jurospehere II germanium array was employed in conjunction with the RITU gas filled recoil separator. The feeding and decay of a 500(20) ns isomeric state in \(^{144}\)Ho has been established for the first time together with states built upon the known 15 \(\mu \)s isomer in \(^{142}\)Tb. The behavior of these new structures above the isomers suggest that they are low deformation configurations which display signs of triaxiality.

abstract

Studies of \(^{225,226}\)U \(\alpha \)-decay chains produced via heavy ion induced fusion reactions of \(^{22}{\rm Ne}+{}^{208}\)Pb\(\rightarrow {}^{230}\)U and of \(^{18}{\rm O}+{}^{208}\)Pb\(\rightarrow {}^{226}\)Th were carried out using the JYFL gas-filled magnetic recoil separator RITU. The data obtained for \(\alpha \)-decays of \(^{225,226}\)U, \(^{221,222}\)Th, \(^{218}\)Ra and \(^{213}\)Rn concerning their \(\alpha \)-particle energies, half-lives and \(\alpha \)-decay fine structures are compared to previous investigations.

abstract

Extensive \({\alpha }\)-decay studies of the very neutron deficient isotopes \(^{191}\)Po, \(^{195}\)Rn, and \(^{196}\)Rn have been performed at the RITU gas-filled recoil separator. The recoil-\({\alpha }\)–\(({\alpha })\) correlation technique and the \({\alpha }\)–\({\gamma }\) coincidence technique have been utilized to unambiguously connect the observed \({\alpha }\)-decays to proper nuclei. Illustrative examples on how the \({\alpha }\)-decay can yield spectroscopic information on the nuclei studied will be presented.

abstract

Very neutron-deficient \(^{191,193}\)Bi nuclei have been studied at the Department of Physics, University of Jyväskylä, Finland (JYFL) employing the Jurosphere II Ge-detector array coupled to the gas-filled recoil separator RITU and different tagging techniques. For the first time in heavy odd-mass nuclei, a collective band (oblate) is identified above the \(2p\)–\(1h\) (1/2\(^{+}\)) proton intruder state in \(^{191}\)Bi. In both \(^{191,193}\)Bi, a band based on isomeric 13/2\(^{+}\) state has been observed and oblate deformation for this state has been deduced.

abstract

The real part of antinucleon–nucleus potential is determined in the framework of the Relativistic Mean Field model using the charge conjugation. The solution of the Dirac equation for antiproton is given in case of \(^{208}\)Pb. The bound state antiprotonic wave functions are compared to those obtained from the pure point charge Coulomb potential. The spectrum of \({\bar p}\) is shown.

abstract

Using scaling rules valid in the liquid drop model of nuclei, as well as universal rules associated with exchanges of stability in families of equilibrium configurations, we constructed closed formulae in terms of the atomic and mass numbers \(Z\) and \(A\) and the angular momentum \(L\), which represent the properties of nuclei rotating synchronously (with ‘rigid’ moments of inertia), as calculated numerically using the Thomas–Fermi model of W.D. Myers, W.J. Swiatecki, Acta Phys. Pol. B27, 99 (1996); Nucl. Phys. A612, 249 (1997); Nucl. Phys. A601, 141 (1996). The formulae are accurate in the range of mass numbers where the transition to rapidly elongating triaxial ‘Jacobi’ shapes takes place. An improved set of formulae is also provided, which takes account of the decreased moments of inertia at low angular momenta. The formulae should be useful in guiding experimental searches for the Jacobi transition. In the second part of the paper we discuss qualitatively some aspects of the dynamics of nucleus–nucleus fusion, and outline a possible way of estimating cross-sections for the synthesis of superheavy nuclei.

abstract

The intensity of secondary radioactive beams has now reached the stage where it is sufficient to perform nucleon transfer reactions with them. Traditionally proven spectroscopic tools such as (\(p,d\)) and (\(d,p\)) reactions must be performed using inverse kinematics, which introduces characteristic experimental constraints. In particular, it is not possible to achieve resolutions better than 200 keV typically, using just the detection of the outgoing charged particles, and gamma-ray detection is required to improve the achievable resolution for bound states. The kinematics are insensitive to the details of individual reactions, so it is possible to construct a dedicated detection system with wide applicability, for example the TIARA array being constructed in the UK for use at GANIL.

abstract

An overview of some recent results on nuclear moment measurements on isomers is being given. Neutron rich isomers have been produced in a fragmentation reaction at GANIL. Using the spin-orientation of the fragment beam, isomeric \(g\)-factors around \(^{68}\)Ni have been measured by detecting the Larmor precession via the isomeric \(\gamma \)-decay (TDPAD-method). Isomers in the mass \(A\sim 180\) region were produced in a fusion-evaporation reaction at Louvain-la-Neuve. The quadrupole moment of a 5 quasi-particle isomer in the deformed nucleus \(^{179}\)W was measured using the Level Mixing Spectroscopy (LEMS) method. Both results show how details on the nuclear structure can be investigated via nuclear moment measurements.

abstract

A major contribution in nuclear astrophysics is expected now and in the near future from the use of radioactive beams. This paper presents an indirect method utilizing radioactive beams to determine the astrophysical \(S\)-factor at the very low energies relevant in stellar processes (tens and hundreds of keV) from measurements at energies more common to the nuclear physics laboratories (10 MeV/nucleon). The Asymptotic Normalization Coefficient (ANC) method consists of the determination from peripheral transfer reactions of the single particle wave function of the outermost charged particle (proton or alpha particle) around a core in its asymptotic region only, as this is the part contributing to nuclear reactions at very low energies. It can be applied to the study of radiative proton or alpha capture reactions, a very important class of stellar reactions. The method is briefly presented along with our recent results in the determination of the astrophysical factor for the proton capture reactions \(^{7}\)Be\((p,\gamma \))\(^{8}\)B and \(^{11}\)C\((p,\gamma \))\(^{12}\)N. The first reaction is crucial for the understanding of the solar neutrino production, the second is a reaction that would bypass the mass \(A=8\) gap in the hot pp chains. Our study was done at the K500 superconducting cyclotron of Texas A&M University (TAMU). Proton transfer reactions with radioactive beams \(^{7}\)Be and \(^{11}\)C produced with MARS were measured, as well as proton transfer reactions involving stable partners. We present the experiments, then discuss the results and the uncertainties arising from the use of calculated optical potentials between loosely bound radioactive nuclei.

abstract

Collective excitations are commonplace features in nuclei at normal deformation. It has been suggested that both in the \(A\sim 190\) and 150 superdeformed (SD) nuclei, collective vibrational states might occur in the same excitation energy range as quasi-particle and single-particle excitations. In particular, the large deformation associated with SD nuclei brings together orbitals from many spherical shells and leads to the close proximity of states with opposite parity, favouring octupole shape vibrations. However, to date, \(\sim 200\) SD bands have been reported in more than 50 nuclei and in most cases, the excited SD bands have been interpreted as single or quasi-particle excitations. Only in very few cases, has the collective excitation scenario been suggested. Where are the collective states in SD nuclei? The question is particularly relevant in even–even \(A=190\) nuclei in which SD states are observed at lower rotational frequency and hence the additional influence of the pair gap makes the collective excitations more competitive with quasi-particle excitations.

abstract

The Time Dependent Resonating Hartree–Fock (TD Res HF) theory is expected to work better than the usual TDHF one if we describe large-amplitude collective motions in soft nuclei with large quantum fluctuations. To make an essential feature of the TD Res HF theory clear, we apply it to the exactly solvable Lipkin model. We adopt an adiabatic perturbative approach to a solution of the TD Res HF equation and derive inertia parameter of kinetic energy and potential energy of the collective motion.

abstract

The dipole response of neutron-rich oxygen nuclei \(^{17-22}\)O has been studied using the electromagnetic excitation process in heavy ion collisions at beam energies around 600 MeV/nucleon. The subsequent neutron decay after inelastic scattering of the secondary beam projectiles on a Pb target was measured in a kinematically complete experiment. Differential electromagnetic excitation cross sections were deduced up to 30 MeV excitation energy. For all isotopes low-lying E1 strength was obtained exhausting between 5% and 12% of the energy-weighted dipole sum rule.

abstract

We analyze the character of the shell effects/Casimir energy in inhomogeneous fermion systems. We estimate magnitude of the shell effects and discuss their dependence on a number of physical parameters (geometry, fermion density, temperature).

abstract

We present some properties of the solutions to the Dirac equation with Woods–Saxon potentials. The results obtained for spherical nuclei are compared to those of the Relativistic Mean Field Theory. A possibility of very significant improvements in the description of single-particle properties is illustrated, and the corresponding choice of the parametrization is presented.

abstract

In this contribution we first recall briefly the basic formulae related to the Dirac mean-field used in conjunction with the Bogolyubov formalism and particle-number projection. We present some results obtained for calculations of the moments of inertia for Super Deformed (SD) bands in the \(A\!\sim \!150\) mass-region, and compare them to the experimental ones. It is shown that this formalism is able to get rid of one of the drawbacks observed in standard Woods–Saxon or Hartree–Fock mean-field calculations, namely the systematic overestimation of the calculated moments of inertia.

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Radii and diffuseness parameters of heavy and superheavy nuclei are analyzed for spherical and axially deformed shapes within the Skyrme–Hartree–Fock+BCS theory with zero-range pairing force.

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The selfconsistent Hartree–Fock calculation with the Gogny effective interaction D1S was performed for the spherical nuclei Ca, Sr, Sn, Sm. The shell effects were extracted by Strutinsky procedure and then the macroscopic energy evaluated by the liquid drop formula. Its parameters and isospin dependent formulae for radii were found.