abstract

An introduction to the workshop at the Mazurian Lakes in honour of Zdzisław Szymański with a short discussion of the situation of nuclear physics in the physics world. The great influence of Zdzisław Szymański on the development of nuclear structure physics, both experimental and theoretical, is emphasized and exemplified with the development of high spin studies in the Rare Earth region.

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Current trends in physics of fast rotating nuclei are reviewed from the theoretical perspective.

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For nuclei with only a few particles outside closed shells, rotational bands might be formed in configurations with holes in the core. Common properties of bands of this kind with hole(s) in the high-\(j\) shells, f\(_{7/2}\), g\(_{9/2}\) and h\(_{11/2}\) are discussed and specific examples are compared with experiment. At superdeformation it is suggested that an approximate decoupling factor for the \(\pi \)[301 1/2] and \(\nu \)[411 1/2] orbitals can be extracted from existing data

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A systematic construction of the energy-density functional within the local density approximation is presented. The Hartree–Fock equations corresponding to such a functional are solved in case of rotating superdeformed nuclei. The identical bands in \({}^{152}\)Dy, \({}^{151}\)Tb, and \({}^{150}\)Gd are investigated and the time-odd components in the rotating mean field are analyzed.

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Properties of octupole vibrations in rapidly rotating nuclei are discussed. Microscopic RPA calculations based on the cranked shell model are performed to investigate the interplay between rotation and vibrations. The ability of this model to describe the properties of collective vibrations built on the ground bands in rare-earth and actinide nuclei is demonstrated at high angular momentum. The octupole vibrational states in even-even superdeformed Hg nuclei are also predicted and compared with available experimental data. A new interpretation of the observed excited superdeformed bands invoking these octupole bands is proposed.

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Several Gammasphere experiments of the past year are presented to illustrate advantages of the increased sensitivity of the new arrays. These involve lifetimes of superdeformed bands, their configurations, enlarging the superdeformed regions, and searching for hyperdeformation.

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Experimental data on \(p\)–\(n\) multiplets appearing in the nuclei near double-magic \({}^{100}\)Sn accessible in heavy-ion fusion-evaporation experiments have been analyzed. Proton-rich nuclei in this region have been investigated using the NORDBALL array. A \({}^{58}\)Ni beams at energies of 270 Mev on \({}^{54}\)Fe and 261 MeV on \({}^{50}\)Cr targets were used. Reaction channel separation was achieved with a 4\(\pi \) charged particle multi-detector set-up together with a 1\(\pi \) neutron detector wall placed in the forward direction. On the basis of \(\gamma \gamma \)-coincidence and angular correlation relations a level schemes of several light Sn, In, Sb, Te and I nuclei were observed for the first time in the present experiment. The observed structure of nuclei are discussed in the framework of the nuclear shell-model. The \(p\)–\(n\) multiplets in the \(A\sim 100\) region corresponding of the nucleon pairs with mixed configurations has been considered as a playground for the tests of the \(T=0\) and \(T=1\) parts of the effective interaction.

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The Thomas–Fermi model of W.D. Myers and W.J. Swiatecki (Nuclear Properties According to the Thomas–Fermi Model, Lawrence Berkeley Laboratory preprint LBL-36557, December 1994, submitted to Nucl. Phys. A; Table of Nuclear Masses According to the 1994 Thomas–Fermi Model, Lawrence Berkeley Laboratory preprint LBL-36803, December 1994) is generalized by the addition of a rotational energy. The results are compared with the calculations of A.J. Sierk (Phys. Rev. C33, 2039 (1986)) on the rotating Yukawa-plus-exponential model. The heights of the fission barriers are estimated for different angular momenta in the case of the super-deformed nuclei \({}^{152}\)Dy and \({}^{83}\)Sr.

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Radio pulsars — rapidly rotating, magnetized neutron stars — are the fastest stellar rotators in the Universe. The structure of rotating neutron stars is determined by the equation of state of matter at supranuclear densities and the angular frequency of rotation. Results of calculations of rapidly rotating neutron star models, performed for a broad set of equations of state of dense matter, are reviewed. The upper limit to rotation frequency of stable rotation results from the appearance of instabilities in rapidly rotating neutron stars. Maximum rotation frequency depends on the equation of state of dense matter, but some general empirical relations between the maximally rotating and static neutron star models are shown to exist.

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Pairing and deformation selfconsistent total routhian surface type calculations with different residual interactions in the particle-particle channel are presented. Calculations involving a separable pairing force of monopole plus quadrupole type are compared to those where a contact force (\(\delta \)-force) is used. The calculations were performed for the superdeformed band \({}^{192}\)Hg and different rotational bands in \({}^{120}\)Cs, \({}^{133}\)Nd and \({}^{135}\)Sm to demonstrate the superiority of state dependent over seniority pairing.

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The possibility of the appearance of the C\(_4\) symmetry in the rotational bands is studied within the particle-rotor model. The role of the triaxiality of the rotor is analyzed.

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We present a semiclassical description of rotating nuclei in the framework of the Extended Thomas–Fermi density functional theory up to order \(\hbar ^2\). It leads to functional expressions of quantities such us the kinetic energy, current and spin vector densities in terms of the local (spin-scalar) density \(\rho (\vec r)\) alone. For effective nucleon-nucleon interactions of the Skyrme type a simple analytical expression is obtained for moments of inertia. It consists, at lowest order, of the Thomas–Fermi (TF) term which is shown to be identical to the rigid-body moment of inertia and semiclassical corrections of order \(\hbar ^2\) which are small. The importance of the Thouless-Valatin selfconsistency terms which are included in our approach, is pointed out. Within this approach we have performed selfconsistent semiclassical calculations in the restricted space of diffuse (Fermi type) densities and ellipsoidal triaxial shapes. Our analysis is qualitatively consistent with LDM results as in the paper by Cohen, Plasil and Swiatecki. However a significant dependence of the LDM parameters as function of the angular momentum has been pointed out. Generalizing our method to finite temperature we recover functional expressions formally similar to the \(T=0\) case with temperature dependent coefficients. The above formalism has also been extended to the semi-quantal description of other large amplitude collective modes and of their couplings. In particular it has been applied to the dynamics of a rigid rotation coupled with a simple (uniform) intrinsic vortical motion.

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The fission probability as a function of the excitation energy in \({}^{236}\)U has been measured for the \({}^{235}\)U(d,pf)\({}^{236}\)U reaction at an excitation energy slightly below the top of the fission barrier, with the aim of disclosing new resonant class III hyperdeformed states in the third minimum of the fission barrier. A strong resonance at E*=5.476 MeV was observed and interpreted as the hyperdeformed ground-state (band). Some weaker resonances around E*\(\approx \)5.3 MeV have also been observed as a consequence of the high energy, dumped superdeformed states.

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The high-spin states in \(^{45}\)Sc, \(^{45}\)Ti and \(^{43}\)Ca were studied with the GASP multidetector array coupled with the Recoil Mass Spectrometer in Legnaro. The nuclei were excited in the \(^{30}\)Si+60 MeV \(^{18}\)O reaction. Life-times were extracted from the analysis of the Doppler shift attenuation of gammas emitted in the reversed kinematics \(^{12}\)C+\(^{35}\)Cl reaction. Energies and the transition probabilities for the observed negative-parity states agree with the shell model predictions. The lifetimes of the intruder-positive parity states in \(^{45}\)Sc and \(^{45}\)Ti suggest a deformation \((\beta \approx 0.25)\) associated with the particle-hole excitation in the nuclei.

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High spin states of \(^{57}\)Co have been studied with the \(^{40}\)Ca(\(^{20}\)Ne, 3p) and \(^{55}\)Mn(\(\alpha \), 2n) reactions at 68 MeV and 25 MeV respectively. The first measurement used \(\gamma \)-\(\gamma \)-recoil coincidences with the OSIRIS \(\gamma \)-spectrometer and the Recoil Filter Detector (RFD). The RFD measured the velocity vector of the fusion evaporation residues; therefore an event by event Doppler correction could be applied with a significant improvement for the \(\gamma \)-energy resolution. The analysis of the \(\gamma \)-\(\gamma \)-recoil coincidence spectra resulted in 43 new \(\gamma \)-transitions of energies between 300 keV and 3300 keV that are assigned to \(^{57}\)Co and established 25 new excited states. Also a DCO analysis has been performed on the present data, however it does not lead to an unambiguous spin assignment for most states as the measured DCO-ratio is often compatible with different spin combinations. The reaction \(^{55}\)Mn(\(\alpha \), 2n) was studied with a compact setup of two Gedetectors. Singles \(\gamma \)- and \(\gamma \)-\(\gamma \)-coincidence spectra were measured. Mainly low spin states were populated, and 26 previously known \(\gamma \)-transitions as well as 21 excited states of \(^{57}\)Co have been confirmed. In this contribution results are presented on \(^{57}\)Co, the nucleus with two neutrons and one proton hole.

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The reaction of \(^{30}\)Si on \(^{58}\)Ni at 134 MeV was used to populate \(^{82}\)Sr and \(^{82}\)Y. The experiment was performed at the C.R.N Laboratory in Strasbourg where the EUROGAM Phase 2 array was used to detect coincident \(\gamma \) rays. Three high spin rotational cascades have been observed, two signature partner bands in \(^{82}\)Sr and one band in \(^{82}\)Y. All three bands exhibit characteristic superdeformed behaviour. The bands have been interpreted as superdeformed bands built upon the [431]1/2 orbital with a \(\pi 5^1\nu 5^2\) intrinsic intruder configuration.

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Isomers in neutron deficient nuclei close to \(^{100}\)Sn were studied with a recoil catcher setup following the reactions \(^{58}\)Ni+\(^{40}\)Ca\(\to ^{98}\)Cd* and \(^{58}\)Ni\(+^{46}\)Ti\(\to ^{104}\)Sn*. New spin gap isomers were found in \(^{92}\)Ru, I\(^{\pi }=(5^-)\), \(t_{1/2}=\)16(2)ns; \(^{95}\)Pd, I\(^{\pi }=(31/2^-)\), \(t_{1/2}=\)12(3)ns; and \(^{94}\)Pd, I\(^{\pi }=(14^+)\), \(t_{1/2}=\)0.8(2) \(\mu \)s. The \(T_z=1\) nucleus \(^{94}\)Pd was identified for the first time in-beam. The decay of the I\(^{\pi }=(8^+)\) isomer in \(^{100}\)Cd was revised leading to the identification of the full set of pure neutron (\(\nu \)) particle and proton (\(\pi \)) hole states below the isomer. The results are compared to large scale shell model calculations with emphasis on the \(\pi \nu \) residual interaction.

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Gamma ray spectroscopy of neutron deficient nuclei close to the dou bly magic nucleus \(^{100}\)Sn has been performed using a heavy-ion reaction and the NORDBALL Ge-detector array. Evaporation residues were identified by means of charged particle and neutron detection. Transitions in 31 different evaporation residues were identified. New results on \(^{102}\)Cd are presented.

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About thirty nuclei in the A \(\sim \) 100 mass region have been produced as fission fragments in the reaction \(^{36}\)S+\(^{162}\)Dy at 162 MeV bombarding energy. They have been individually identified from their \(\gamma \)-ray transitions detected using an early implementation of EUROGAM array. The mass region reached develops from \(Z=34\) (Se) to \(Z=48\) (Cd) and from \(N=46\) to \(N=66\), along the valley at stability and beyond it towards neutron-rich side. Level schemes of already known stable or neutron-rich nuclei have been extended to higher spins. From cross coincidences between transitions in complementary fragments, \(\gamma \)-rays de-exciting high-spin states of new isotopes have been identified and some aspects of the fission mechanism have been analyzed.

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The properties of rotational bands in the \(A\sim 110\) \((Z\geq 50\), \(N\sim \) 56–65) mass region are investigated within the configuration-dependent shell-correction approach with the cranked Nilsson potential. It is shown that in nuclei with \(Z\geq 50\), \(N\leq 60\), smooth terminating bands based on two proton holes in the \(g_{9/2}\) subshell might be observed over a wide spin range up to termination. In the \(N\gt 60\) nuclei, the terminating states of such bands reside well above the yrast line in calculations. The results of calculations are consistent with available experimental data.

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The study of \(^{193}\)Tl, using EUROGAM phase 2 gamma array, revealed five superdeformed bands (SD) in this nucleus. The measured value of \(gK=1.4pm0.17\) for the two signature Yrast SD bands confirms the [642]5/2 intruder configuration for the odd proton. A saturation of the dynamic moment of inertia \(I^2\) is observed for these two bands. It can be understood in terms of an exhausted quasi-neutron alignment in the presence of substantially reduced quasi-proton alignment due to the Pauli blocking. From band interactions and \(I^2\) behaviours, intrinsic configurations involving the [411]1/2 and [651]1/2 proton orbitals, are assigned to the excited SD bands.

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The superdeformation in \(^{191}\)Au has been studied with EUROGAM II. The yrast superdeformed band has been extended to very high rotational frequencies and a new excited band has been observed. The dynamical moment of inertia of the yrast SD band exhibits an interesting saturation feature at the highest rotational frequencies. An interpretation is proposed in terms of blocked SD proton orbitals.

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The heavy-ion collisions of \(^{232}\)Th + \(^{136}\)Xe and \(^{232}\)Th + \(^{56}\)Fe with beam energies 15–20% above the Coulomb barrier have been used to populate nuclei in and around the actinide region of the nuclear chart. The product yield distributions of the binary reaction products stopped in thick targets have been obtained by measuring \(\gamma \)-\(\gamma \) coincidence intensities. A comparison of the distributions for the two reactions shows that the transfer of nucleons is dictated by the mass and charge equilibration processes. This suggests that \(^{136}\)Xe is the better projectile for populating the region of octupole-deformed nuclei which are inaccessible by compound-nucleus reactions.

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In the last few years, our understanding of nuclei at extremes of stability has undergone substantial development and change. It is now thought that there is every likelihood for truly new manifestations of structure at extreme \(N/Z\) ratios, unlike anything observed to date. Changes in shell structure, residual interactions, symmetries, collective modes, and the evolution of structure are envisioned. These developing ideas expand the opportunities for nuclear structure studies with radioactive beams and focus attention on the need to develop efficient experimental techniques and improved signatures of structure. These developments are discussed along with an overview of current and future radioactive beam projects in North America.

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The Coulomb field of a heavy nucleus provides an intense source of quasi-real photons acting on passing nuclear particles. This fact has many applications in studies of nuclear structure problems. Coulomb dissociation of fast projectiles has been proposed as a novel method to investigate radiative capture processes (time-reversed to photodisintegration). This is a new access to a specific class of radiative capture reactions at low energies, relevant for nuclear astrophysics, and it does overcome various limitations of direct measurements. This lecture puts emphasis on a general discussion of the favourable experimental conditions, of related theoretical problems of the analysis and possible pitfalls of the approach. Various cases of actual astrophysical interest and current applications are discussed.

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In experiments at the SIS facility at GSI Darmstadt systematic studies of the directed sideward flow in central and semi-central heavy ion collisions have been performed. The symmetric systems Ni\(+\)Ni and Au\(+\)Au were investigated at energies between 100 and 2000 \(A\)MeV with FOPI, a \(4\pi \) detection system for charged particles. For the first time the flow patterns, represented by the in-plane transverse momentum per nucleon or the azimuthal emission distribution at midrapidity have been investigated for intermediate mass fragments \((Z\geq 3)\) as well as for the secondary products \(\pi ^+, \pi ^-, K^+, K^0_s\), and \({\mit \Lambda }\)-particles. As known from many earlier studies the fragments show a clear flow signal, stronger than that of the light charged particles or nucleons. Both \(\pi ^+\) and \(\pi ^-\) display an almost vanishing signal. The same is true for the strange products \(K^+\) and \(K^0\) whereas the \({\mit \Lambda }\)-particles, co-produced with the \(K^+\), show a distribution very similar to the proton signal.

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A brief overview is given of recent advances towards extending the nuclear Boltzmann model to processes exhibiting instabilities and associated catastrophic bifurcations, by incorporating the fluctuating part of the collision term in the equation of motion for the one-body phase-space density.

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Subthreshold bremsstrahlung photons are shown to be a unique probe of nuclear matter when it is in a well defined thermodynamical phase during a heavy-ion collision. From their emission pattern which closely follows the nuclear reaction dynamics we deduced a new interpretation of the two-photon correlation function. We also show that very energetic photons are produced but their origin cannot solely be explained by the bremsstrahlung process and the known hadronic contributions.

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A brief description is given of the Hanbury-Brown–Twiss effect method for determining the space-time structure of the proton-emitting source in a nucleus-nucleus collision. In this context a measurement of exclusive p-p correlations from \({}^{58}\)Ni+\({}^{58}\)Ni at 850 MeV is analyzed. The data served to study the directional dependence of the p-p correlation function and, for the first time, extract separately the source size and the particle-emission time.

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The \(\gamma \) decay of the Giant Dipole Resonances, GDR, coupled to excited states in hot nuclei is discussed. We concentrate on the evolution of the experimental methods tending towards larger selectivity, i.e. determination of the quantities measured in a specific region of excitation energy and angular momentum of a particular, identified nucleus. We present also some representative examples of the studies in which GDR was used as a tool to obtain information about hot, fast rotating nuclei. The first experiments attempting to study the dilepton decay of the Giant Monopole Resonance in hot nuclei are briefly discussed.

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Cooler-storage ring facilities offer unique experimental possibilities for the study of electron-ion recombination processes at low relative energies by employing the electron cooler as a target. Through the use of an adiabatically expanded electron beam in the cooler of CRYRING, reactions down to \(10^{-4}\) eV relative energies can be measured at an energy resolution in the order of \(10^{-2}\) eV FWHM with ions stored in the ring at around 10 MeV/amu energies. A review of our measurements of radiative recombination, laser stimulated recombination, and dielectronic recombination is presented.

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The storage of exotic particles like antiprotons, radioactive isotopes, or highly charged ions in ion traps or storage rings has made possible high-accuracy experiments. This publication concentrates on mass spectrometry and lifetime measurements of such species. The principle of ion storage and recent experiments will be discussed.

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A survey on the fundamental structure aspects of very heavy few-electron ions, in particular H-like systems, is presented. Special emphasis is given to contributions from quantum-electro-dynamics at strong central potentials. The technical possibilities to produce highly-charged heavy ions are reviewed and the ground-state Lamb-shift experiments performed at the heavy ion storage ring ESR are summarized. A short outlook on further developments in this field is added.

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The measurement of the electronic \(g\)-factor of hydrogenic ions is a sensitive test of bound-state QED (Quantum Electrodynamics). The deviations of the \(g\)-factor of the bound electron from the free-electron value are mainly due to (i) the relativistic binding energy correction \(-(Z\alpha )^2/3\) and (ii) the bound-state radiative correction \(\alpha (Z\alpha )^2/4\pi \). In the experiment a single hydrogenic ion is stored in the magnetic field of a Penning trap. The \(g\)-factor is measured by inducing spin-flip transitions with a microwave field. The magnetic field is calibrated measuring the cyclotron frequency of the stored ion. In the Penning trap the ion is detected electronically and cooled to \(4^{\circ }\) K through a superconducting resonance circuit connected to the trap electrodes.

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Supercritical electromagnetic fields are predicted to lead to spontaneous emission of positrons in nuclear systems with \(Z\gt 173\). A possible route to identify spontaneous positron creation is discussed. The radiative quantum electrodynamical corrections are calculated. Their contribution amounts to about one per cent of the electron binding energy in nearly critical systems. The formation of supercritical high-\(Z\) quasiatoms in heavy-ion collisions is investigated, and the use of \(\delta \)-electron spectra as measurement tool for nuclear delay times and electron binding energies in superheavy quasiatoms is pointed out. Positron creation by dynamical processes and internal pair conversion is evaluated.

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Results are presented from a new experiment, APEX, designed to study the previously reported sharp lines in sum-energy spectra of positrons and electrons produced in collisions of very heavy ions. Data have been collected for \(^{238}\)U + \(^{181}\)Ta and \(^{238}\)U + \(^{232}\)Th. No evidence is found for narrow structures similar to those previously reported. For the specific case of the isolated decay of a neutral particle of mass 1.4–2.1 MeV/c\(^2\), the upper limits on cross sections obtained are significantly less than previously reported. Data are also presented for internal pair conversion in \(^{206}\)Pb. These results are used to set limits for the possible contribution to the pair yield of a 1780 keV transition in \(^{238}\)U observed in heavy-ion gamma-ray coincidence measurements.

abstract

The decay of vector mesons into lepton pairs (e\(^+\) e\(^-\) or \(\mu ^+\,\mu ^-\)) offers a very nice channel to study their relation to time-like photons in free space and their properties in the nuclear medium, as the emitted leptons are not distorted by strong interactions. This paper summarizes the known aspects of vector meson physics, discusses some recent theoretical developments and indicates the new experimental perspectives opened in this field by large acceptance dilepton detectors.

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A High Acceptance DiElectron Spectrometer (HADES) has been proposed at the SIS accelerator of GSI in order to measure e\(^+\)e\(^-\) pairs produced in proton, pion and heavy ion induced reactions. HADES will be able to operate at the highest luminosities available at SIS in an environment of high hadron and photon background. A Ring Imaging Čerenkov Counter (RICH) serves for electron identification. Momentum measurement is achieved with a magnetic spectrometer consisting of superconducting toroidal coils and mini drift chambers for tracking. Arrays of pre-shower detectors and a Time Of Flight wall are positioned behind the drift chambers for electron trigger purposes and for measuring the charged particle multiplicity. The detector features have been investigated in detailed simulations. The expected performance of the system in terms of efficiency, resolution and residual background is presented. First results from prototype tests of HADES detectors are briefly discussed.

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The current progress of spectroscopic studies of helium like systems will be reviewed. Special emphasis will be given to both the groundstate as well as to the excited state investigations. For the heaviest ions, the potential of precision spectroscopy will be outlined and its relevance for atomic structure investigations will be discussed.

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Two experiments aimed at measuring the masses of secondary ions of \(A=100\) in the vicinity of \(^{100}\)Sn have recently been performed, using the second cyclotron of GANIL (CSS2) as a high resolution spectrometer. The first experiment provided very encouraging preliminary results on the masses of \(^{100}\)Cd and \(^{100}\)I, we reproduced with a precision of \(\sim 100\) keV the known mass excess of \(^{100}\)Cd and we measured for the first time the mass of \(^{100}\)I with a precision of \(5\times 10^{-6}\). The relative mass differences between the \(A=100\) secondary ions are less than \(3\times 10^{-4}\), and they can thus be simultaneously accelerated in CSS2. In the second experiment — which was run in late July 1995 — we used the same method with a slightly different set-up and it is envisaged that the mass of \(^{100}\)Sn will be determined (we observed very likely about 10 events of \(^{100}\)Sn\(^{22+}\)). The data analysis is in progress.

abstract

The quality of the description of nuclear masses by various microscopic approaches is studied. Hartree–Fock–Bogolubov, Extended Thomas–Fermi model with Strutinski Integral, Relativistic Mean Field and Macroscopic-Microscopic approaches are considered. Spherical even-even nuclei (116 nuclides) from light (\(A=16\)) to heavy (\(A=220\)) ones with known experimental mass are chosen for the study.

abstract

A description is given of the novel electron spectrometer SACRED, which uses a multi-element Si array to detect cascades of conversion electrons. Its application to the study of “shears” bands in \(^{199}\)Pb and highly deformed structures in \(^{222}\)Th is also described.

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In the paper the physical quantum numbers labelling the irreducible representations of the point symmetry \(D_{3h}\) have been derived. Both sets of labels, obtained in the intrinsic and laboratory frames, have been considered. This symmetry is related to the octupole deformation of \(\alpha _{33}\)-type which leads to the exotic octupole states of nuclei. The derivations are based on a group algebra formalism.

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Nuclei with extreme neutron to proton ratios, which are in most cases not accessible to experimental investigations, play an important role in astrophysics. For such nuclei near the particle drip-lines new structure effects are expected. Hartree–Fock–Bogoliubov (HFB) calculations with the SkP interaction show modified nuclear potential wells which may be simulated by a Nilsson potential with vanishing \(l^2\)-term. The influence of this modification on the \(\beta \)-decay properties of very neutron-rich nuclei is studied within the framework of the QRPA.

abstract

Using the Munich Q3D spectrograph the \(^{154}\)Sm(\(\vec {\rm d}\),t), (d,t), (p,d), and (\(^3\)He,\(^4\)He) \(^{153}\)Sm reactions have been measured at beam energies between 23 and 32 MeV. The high resolution of up to 4 keV FWHM especially in (p,d) is essential to achieve reliable energy calibration. All levels reported in the Nuclear Data Sheets [1] with the exception of high spin states (\(J\geq \)13/2) are observed and at higher excitation energy (\(E_x\)>1 MeV) many new levels could be identified. The analysis in the framework of the Nilsson model uses CCBA to include inelastic transfer amplitudes.

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Low-lying energy levels and electromagnetic transitions in Ba isotopes were obtained using the new method of solving the general Bohr Hamiltonian. Inertial functions and collective potential were calculated within the cranking approximation with the projected BCS formalism and Seo parameters for the Nilsson single-particle potential.

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From the \(\gamma \)-\(\gamma \) coincidence data and radioactivity analysis nearly complete distributions of products for \(^{208}\)Pb + 350 MeV \(^{64}\)Ni and \(^{130}\)Te + 275 MeV \(^{64}\)Ni reactions were established. The results are discussed in terms of the equilibration of \(N/Z\) ratio in deep-inelastic (massive transfer) processes. Comparison with model calculations suggests a significant deformation of nuclei at the scission point.

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A general formula for the correlation of two polarized gamma quanta emitted in a cascade from oriented nuclei is given. The case of polarizational directional correlation of photons emitted from an aligned nucleus is discussed.

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Fluctuations in distributions of nuclear fragments produced in central Au + Au collisions at laboratory energies of 150\(A\) and 400\(A\) MeV were analyzed by means of normalized scaled factorial moments. No variation of the moments with bin width was found for charge distributions. An intermittency signal was found for distributions of fragments in azimuthal angle. A similar analysis performed for events simulated with the IQMD model did not show any intermittency.

abstract

The surface vibrations in nuclear Fermi liquid are studied within a phase space approach which is based on the Landau–Vlasov kinetic equation. The linear response theory is used. We focus on the damping of low frequency surface vibrations and discuss their friction coefficient.

abstract

Fast-fission reactions in collisions of four heavy systems (well below the fusion extra-push energy threshold), for which Hinde and coworkers had measured the prescission neutron multiplicities, have been analysed in terms of the deterministic dynamic model of Feldmeier coupled to a time-dependent statistical cascade calculation. In order to reproduce the measured prescission multiplicities and the observed (nearly symmetric) mass divisions, the energy dissipation must be dramatically changed with regard to the standard one-body dissipation: In the entrance channel, in the process of forming a composite system, the energy dissipation must be reduced to at least half of the one-body dissipation strength (\(k_{s}^{in}\leq \) 0.5), and in the exit channel (from a mononucleus shape to scission) it must be increased to about 10 times that value (\(k_{s}^{out}\approx \) 10).

abstract

There is strong experimental evidence that low energy fusion-fission reactions are accompanied by an emission of alpha particles whose characteristics cannot be explained by statistical pre-scission emission from the compound system nor by post-scission emission from the accelerated fission fragments. These particles are found at angles close to 90 degrees (with respect to the fission axis). They seem to originate from the neck area of the system and be emitted near scission. We discuss possible mechanisms responsible for their emission and present a dynamical study of their motion in the Coulomb and nuclear fields of the separating fission fragments.

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Spontaneous fission half-lives of the Fm isotopes are analyzed in a multidimensional collective space. The parameters describing the shape of nuclei \(\{\beta _\lambda \}\), \(\lambda =\) 2,3,4,5,6,8 and the pairing degrees of freedom \(\Delta _p\) and \(\Delta _n\) are taken into account. The half-lives \(T_{sf}\) are calculated by the WKB method. We propose the ‘optimal’ collective space (\(\beta _2\),\(\beta _4\),\(\beta _6\),\(\Delta _p\),\(\Delta _n\)) for dynamical calculations of the spontaneous fission half-lives of nuclei in this region. The \(T_{sf}\) for the even-even Fm isotopes are calculated.

abstract

Microscopic calculations of the mean square charge radius of Ag, Rb and Sn isotopes are presented. The model bases on the Nilsson single particle potential and the BCS theory.

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Preliminary results of experiments combining an array of large BaF\(_2\) detectors for high energy gamma-rays with an array of 17 Anti-Compton spectrometers are presented. The correlation between excited state giant dipole resonances and discrete line structures are discussed. Indications of the low lying components of GDR built on superdeformed \(^{143}\)Eu are shown.

abstract

A multidetector set-up has been developed for the detection of photons between 5 and 40 MeV. It consists of 10 cm x 10 cm BGO cylinder shielded with active and passive shields against the cosmic-rays and the \(\gamma \)-ray background and of a multiplicity filter consisting of 28 detectors (BaF\(_2\) and NaI(Tl)). The neutrons are discriminated with TOF. The system is installed at the new Warsaw Cyclotron. It is intended for studies of giant dipole resonances in hot nuclei and of bremsstrahlung at low beam energies. The first experiments and the plans for further development of the set-up are described.

abstract

The procedures to deduce the incompressibility modulus of nuclear matter, \(K_0\), from the measured energies of the Isoscalar Giant Monopole Resonances, \(E_{GMR}\), are critically reviewed. A simple model is developed in which the isoscalar density oscillations in finite nuclei are described as being due to the coupling of two modes: the bulk (scaling) mode and the surface mode. Two energy solutions are obtained for the coupled mode: the low energy solution, which is presumably the one observed experimentally, and the high energy one, well above the range of the present experiments.

abstract

Single proton localization in the neutron matter is studied by means of the self-consistent Hartree-Fock calculations. Ranges of the total density in which the localization is possible are derived and the corresponding proton and neutron density profiles are presented. Perspectives of the full inclusion of spin degrees of freedom are discussed.

abstract

The correlation of polarization of annihilation quanta has been measured in order to test the Bell’s inequality. Significant violation of the Bell’s inequality and a good agreement with predictions of quantum mechanics have been ascertained.

abstract

For 82–170 MeV/u Bi \(\to \) Ni collisions the total as well as final state sensitive cross sections for non-radiative electron capture have been measured. Due to the large shell and subshell splitting in such a high-\(Z\) projectile the applied \(x\)-ray/particle coincidence method enables us to probe the theoretical predictions even with respect to the final orbital momentum dependency of this capture mechanism. For the case of the “higher potential” version of the eikonal approximation good agreement with the total cross sections data is obtained. However, the orbital momentum dependence given by the same theoretical formulation is at variance with the experimental findings.

abstract

The motion of a particle with a spin in spherical harmonic oscillator potential with spin-orbit interaction is discussed. The attention is focused on the spatial motion of wave packets. The particular case of wave packets moving along the circular orbits for which the most transparent and pedagogical description is possible is considered. The splitting of the wave packets into two components moving differently along classical orbits reflects a strong analogy with the Stern–Gerlach experiment. The periodic transfer of average angular momentum between spin and orbital subspaces accompanying this time evolution is called the spin-orbit pendulum.