Hunting η-bound nuclei

The η meson can be bound to atomic nuclei.Experimental search is discussed in the form of final state interaction for the reactions dp → 3 Heη and dd → 4 Heη.For the latter case tensor polarized deuterons were used in order to extract the s-wave strength.For both reactions complex scattering lengths are deduced: a 3 Heη = ± 10.7±0.8 +0.1 -0.5 +i· 1.5±2.6 +1.0-0.9 fm and a 4 Heη = [±(3.1±0.5)+i·(0±0.5)] fm.In a two-nucleon transfer reaction under quasi-free conditions,p 27 Al → 3 HeX,was investigated.The system X can be the bound 25 Mg  η at rest.When a possible decay of an intermediate N  (1535) is required,a highly significant bump shows up in the missing mass spectrum.The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ=4.4±1.3 MeV.     

Hunting η-bound nuclei

The η meson can be bound to atomic nuclei.Experimental search is discussed in the form of final state interaction for the reactions dp → 3 Heη and dd → 4 Heη.For the latter case tensor polarized deuterons were used in order to extract the s-wave strength.For both reactions complex scattering lengths are deduced： a 3 Heη = ± 10.7±0.8 ＋0.1 -0.5 ＋i· 1.5±2.6 ＋1.0-0.9 fm and a 4 Heη = [±（3.1±0.5）＋i·（0±0.5）] fm.In a two-nucleon transfer reaction under quasi-free conditions,p^ 27 Al → ^3 HeX,was investigated.The system X can be the bound 25 Mg  η at rest.When a possible decay of an intermediate N  （1535） is required,a highly significant bump shows up in the missing mass spectrum.The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ=4.4±1.3 MeV.     

Shape coexistence of superheavy nuclei

Shape coexistence appears in the region of superheavy nuclei. Calculations for the nobelium isotopes have been carried out with the cranking TRS model. It shows that normal deformed and superdeformed prolate shapes coexist. Particularly for the nuclei ^248,250No, the ground states are superdeformed. The kinematic moments of inertia are calculated and they agree well with available experimental results. As rotational frequency increases, the     

π-Meson absorption by three-particle nuclei

The reactions ⁺ +³He 3p and ^– +³H 3n are considered with both two- and three-nucleon pion-absorption taken into account. The pion-absorption with all nucleons of the nucleus involved and the interference of the two absorption mechanisms are shown to be of the same importance as a pure two-particle absorption in nuclei. The latter cannot be considered dominating as it used to be.     

Photoproduction of πmesons from nuclei

Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead) has been studied for incident-photon energies from 200 MeV to 800 MeV with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data were obtained for the inclusive photoproduction of neutral pions and the partial channels of quasifree single- , double- , and photoproduction. They have been analyzed in terms of the in-medium behavior of nucleon resonances and the pion-nucleus interaction. They are compared to earlier measurements from the deuteron and to the predictions of a Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon-induced pion production from nuclei.PACS: 13.60.Le Meson production - 25.20.Lj Photoproduction reactions     

η-nucleus bound states in nuclei

The binding energies εη and widths Гη of wmesic nuclei are calculated. We parameterize the η self-energy in the nuclear medium as a function of energy and density. We find that the single-particle energies are sensitive to the scattering length, and increase monotonically with the nucleus. The key point for the study of η-nucleus bound states is the η-nuclear optical potential. We study the s-wave interactions of η mesons in a nuclear medium and obtain the optical potential Uη ≈ -72 MeV. Comparing our results with the previous results, we find that the ηN scattering length aηN is indeed important to the calculations. With increasing nuclear density the effective mass of the η meson decreases.     

η-nucleus bound states in nuclei

The binding energies η and widths Γη of η-mesic nuclei are calculated.We parameterize the η self-energy in the nuclear medium as a function of energy and density.We find that the single-particle energies are sensitive to the scattering length,and increase monotonically with the nucleus.The key point for the study of η-nucleus bound states is the η-nuclear optical potential.We study the s-wave interactions of η mesons in a nuclear medium and obtain the optical potential Uη≈ -72 MeV.Comparing our results with the previous results,we find that the ηN scattering length aηN is indeed important to the calculations.With increasing nuclear density the effective mass of the η meson decreases.     

Anharmonicities of γ-vibrations in deformed nuclei

The anharmonicities of γ-vibrations are studied within the multiphonon method in different even-even deformed nuclei where the first K^π = 2⁺ vibrational state appears well below the energy gap: ¹³⁰Ce, ^162–164Dy, ^164–168Er, ¹⁸⁶Os. The anharmonicities previously obtained in ¹⁶⁸Er appear to be a general property of these nuclei.     

Decay properties of N ≃ Z nuclei

This review focusses on recent results obtained by using fusion-evaporation reactions for the production of N ≃ Z nuclei, the on-line mass separator of GSI for the preparation of the radioactive samples, and charged-particle and γ-ray detectors for performing decay spectroscopy. The experimental results on prompt and β-delayed disintegration modes are discussed in comparison with theoretical model predictions. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: e.roeckl@gsi.de     

Superheavy nuclei — cold synthesis and structure

The quantum mechanical fragmentation theory (QMFT), given for the cold synthesis of new and superheavy elements, is reviewed and the use of radioactive nuclear beams (RNB) and targets (RNT) is discussed. The QMFT is a complete theory of cold nuclear phenomena, namely, the cold fission, cold fusion and cluster radioactivity. Also, the structure calculations based on the axially deformed relativistic mean field (DRMF) approach are presented which predict new regions of spherical magicity, namely Z=120 and N=172 or 184, for superheavy nuclei. This result is discussed in the light of recent experiments reporting the cold synthesis of Z=118 element.     

Indirect interaction of Mössbauer nuclei

An expression is deduced for the operator of the indirect interaction of nuclei via the electromagnetic field. The properties of Mössbauer nuclei are described within the pseudospin formalism, which is usually used in the theory of optical two-level systems. The indirect interaction of pseudospins is derived by a method adopted from the theory of superconductivity. It is found that the potentials of this interaction involve terms decreasing as r ^?3, r ^?2, and r ^?1. The estimates demonstrate that the two-particle interaction can contribute significantly to the width of the resonance line, for example, in crystals whose cells contain thulium nuclei.     

α preformation and penetration probability for heavy nuclei

The α preformation factor and penetration probability have been analyzed for even--even nuclei of Po, Rn, Ra using experimental released energies and α decay half-lives in the frame of the double folding model. It is shown that N=126 is a neutron magic number from α preformation and shell effects play an important role in α preformation. The closer the nucleon number is to the magic number, the more difficult α formation in the parent nucleus is. The preformation factor can supply information on the nuclear structure and the penetration probability mainly determines α decay half-life.     

Green’s function calculations of light nuclei

The influence of short-range correlations in nuclei was investigated with realistic nuclear force. The nucleon-nucleon interaction was renormalized with V_lowk technique and applied to the Green’s function calculations. The Dyson equation was reformulated with algebraic diagrammatic constructions. We also analyzed the binding energy of ⁴He, calculated with chiral potential and CD-Bonn potential. The properties of Green’s function with realistic nuclear forces are also discussed.     

Spherical and Deformed Shell Closures in Superheavy nuclei

The structure of superheavy nuclei has been studied using the macroscopic-microscopic model. The macroscopic energy was calculated with the continuous medium model in which the energy is expressed as a function of nucleon densities. The deformations and structures of superheavy nuclei were systematically investigated. Calculations reproduce well the available data of experimental α-decay energies and half-lives. The investigation of single-particle levels shows that the shell structure is deformation and isospin dependent. Potential-energy-surface calculations display that superheavy nuclei have in general harder shapes than the nuclei of other mass regions.     

Photoproduction of π + p pairs on nuclei

The photoproduction of pion-nucleon pairs on nuclei was analyzed. The contributions of both nucleonic and isobar configurations in the ground state of nuclei were taken into account. The cross section for the photoproduction of pion-proton pairs in the reactions ¹⁶O(??, ?? ⁺ p)¹⁵C and ¹²C(??, ?? ⁺ p)¹¹Be were calculated.     

Structure of neutron-rich nuclei around A ⋍ 100

Neutron-rich isotopes of Mo (Z=42) around A ⋍ 100 have been investigated within the formalisms of cranked Nilsson Strutinsky and CHFB, to study several interesting features of nuclear structure in this mass region. The total energy/routhian surfaces have been generated for the isotopes of Mo ranging from A ⋍ 96 − 112, as a function of deformation (β ₂ and γ) for ground state and higher angular momentum states. Results of calculations using two different formalisms have been compared and combined to have a better understanding of the underlying mechanism of shape evolution.     

Role of 8Be → 2 α intermediate nuclei in the fragmentation of 16O relativistic nuclei in nuclear track emulsions

In searches along a track in the chamber irradiated at the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna) with oxygen ions accelerated to a momentum of 4.5 GeV/c per nucleon, 215 events containing two or more doubly charged fragments of the primary nucleus were found. Emission angles in the track-emulsion plane were measured in these events. Their distribution is consistent with that which alpha particles are expected to have in an oxygen nucleus prior to its interaction with a track-emulsion nucleus. Events of the ¹⁶O ?? 2⁸Be ?? 4?? type were discovered for the first time. They are treated as events of the coherent electromagnetic dissociation of an oxygen nucleus. Among all events, about 14% of the ⁸Be ?? 2?? decays proceed through the ground state of spin-parity 0⁺; an approximately the same fraction of such decays proceed through the first excited state of spin-parity 2⁺.