Excited collective states of heavy even-even nuclei

Quadrupole-type collective excitations of even-even nuclei are analyzed. In this analysis, transverse γ vibrations of the nuclear surface are taken into account effectively, while longitudinal beta vibrations remain free. A potential energy of the exponential form is used for free surface longitudinal beta vibrations. The behavior of the energy levels of excited states in the ground-state, β, and γ bands of heavy nuclei is studied, and the predictive potential of the model used is demonstrated for transfermium nuclei.     

Theory of the excited states of deformable even-even nuclei

The excited states of nonspherical even-even nuclei are discussed taking the change in nuclear shape during excitation into account.     

Excited states of deformable nonaxial odd nuclei

Rotationally single-particle and vibrational excitations of deformable nonaxial odd nuclei are investigated with allowance for the interaction of collective and single-particle states. The ratios of excitation energies, of reduced probabilities of E2 transitions, and of quadrupole moments for deformed nonaxial odd nuclei are calculated up to high-spin states.     

A calculation of low-lying collective states in even-even nuclei

We present results of a calculation of the low-lying collective quadrupole states in even-even nuclei within the framework of the proton-neutron interacting boson model.     

Excited states of muonium in atomic hydrogen

Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron—hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton—hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation     

A shell-model description of 0+ intruder states in even-even nuclei

Starting from the nuclear shell structure in medium-heavy and heavy nuclei, the excitation energy for low-lying 0⁺ intruder states is studied. Taking as a simplified model two particle-two hole (2p-2h) excitations across closed shells, the effects of the pairing and the proton-neutron (monopole and quadrupole component) residual interaction on the unperturbed energies are calculated. Application to major closed-shell (fZ = 50, Z = 82) and to subshell (Z = 40, Z = 64) regions is performed. We especially concentrate on 0⁺ intruder states in the even-even Pb nuclei.     

Transition probabilities and static moments of excited states in even-even nuclei

A new approach is made to calculate the generalized single-particle density matrixp ^μv in even-even nuclei. It is shown that this quantity is included in the three particle response function, for which we derived a renormalized equation. Taking into account in a consequent way the effective particle-hole interaction we received a formula for the static moment of excited states and the transition probability between such states which is essentially different from the usual RPA theory.     

A method of angular momentum projection for excited states in even-even nuclei

A method of angular momentum projection for the excited states in even-even nuclei is formulated within the framework of the Hartree-Bogoliubov theory. A preliminary application of this method is performed for the K=0^? band in ¹⁶²Er.     

Subthreshold photofission of even-even nuclei

Within quantum-mechanical fission theory, the angular distributions of fragments originating from the subthreshold photofission of the even-even nuclei ²³²Th, ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu are analyzed for photon energies below 7 MeV. Special features of various fission channels are assessed under the assumption that the fission barrier has a two-humped shape. It is shown that the maximum value of the relative orbital angular momentum L _m of fission fragments can be found upon taking into account deviations from the predictions of A. Bohr’s formula for the angular distributions of fission fragments. The result is L _m ≈ 30. The existence of an “isomeric shelf” for the angular distributions of fragments from ²³⁶U and ²³⁸U photofission in the low-energy region is confirmed.     

Excited atomic and molecular states in strong electromagnetic fields

Large changes in atomic and molecular structure can occur when strong static or oscillating electromagnetic fields are present. Such fields also can ionize atoms. Strong oscillating fields induced multiphoton transitions between bound states as well as to the continuum. What is known about these phenomena is reviewed, with emphasis on theories and experiments concerned with the field-sensitive excited and highly-excited states.     

Excited states in neutron deficient even-even thorium isotopes (218≦A≦222)

The nuclei^{218, 220, 222}Th were investigated by conversion electron andγ-ray spectroscopy after compound nucleus reactions of¹⁴N with²⁰⁹Bi and^{16, 18}O with²⁰⁸Pb. The intenseγ-background from fission was suppressed by spectroscopy of conversion electrons andγ-rays in coincidence with the evaporation residues or theirα-decay. Level schemes were determined for²¹⁸Th up toI ^π=10⁺ and for²²⁰Th and²²²Th up toI ^π=15^?. The observed structure of²¹⁸Th may be explained in the spherical shell model with residual interaction by two neutron excitation. ForN≧130 completely different level schemes are observed showing very intense, collective electric dipole transitions (B(E1)?10^?2 W.u.) with energies of typically 200 keV. Interpretation in terms of stable octupole deformations of the ground state as well as in anα-cluster picture are discussed.     

Binding energies of even-even superheavy nuclei

The structure of the even-even superheavy nuclei with the proton number Z=98–110 is studied using the self-consistent relativistic mean-field theory. The calculated binding energies are in good agreement with the available experimental ones. An upper limit and a lower limit on the binding energies are set by the calculations. This is useful for future calculations of properties of superheavy nuclei and for the experimental synthesis of superheavy nuclei. The energy surface of some relevant superheavy nuclei is also given and it confirms the correctness of the calculations.     

On symmetry energy of even-even nuclei

A density dependent contact force whose parameters are derived from the requirements of translational invariance and gauge invariance is applied to spectroscopic studies in²⁰⁸Pb. It is shown that spectroscopic studies of states of natural parity and of electric multipole transitions yield no physically significant, additional information on force parameters compared to the translational invariance subsidiary condition.     

From regular to chaotic states in atomic nuclei

This work has been partially supported by the Ministero dell’Università e della Ricerca Scientifica e Tecnologica (MURST) and by the INFN-CICYT Agreement.     

Cluster states in atomic nuclei and cluster-decay processes

The relationship between decay properties of nuclei (primarily cluster properties) and cluster-decay characteristics is discussed. Both purely microscopic and microscopically substantiated semimicroscopic and semiempirical methods are considered. The current state of the proton-, α-, and cluster-radioactivity theory is presented.     

Fission barriers for even-even actinide nuclei

Fission barriers for even-even nuclei in the region (Th ... Ku) are calculated in the framework of the Strutinsky method and using the concept of dynamic fission paths. The single particle states are calculated in a deformed Woods-Saxon potential including axial asymmetry at the inner barrier and deviation from reflection symmetry at the outer barrier. It is shown that in the present model also the mass symmetric outer barrier is unstable against axially asymmetric (γ) distortions.     

Properties of the low-lying excited states in even-even nuclei around the closed shell N=82

The properties of low-lying states in ¹³⁶Ba and ¹⁴⁴Nd are calculated within the quasiparticle phonon model. It is shown that the strong quadrupole interaction in the particle-particle channel leads to the appearance of low-lying isovector excitations. Due to this reason, there are two branches in the lowlying part of the spectrum, an isoscalar and an isovector one. Both branches show peculiar regularities of E2 and M1 transitions.     

Excited states of deformable odd <Superscript>157,159</Superscript>Tb nuclei: Nonconservation of the angular momentum of external nucleon

The previously developed rotationally single-particle and vibrational model of the triaxial deformable odd nuclei is extended to the case where the total angular momentum of an external nucleon is not conserved. The calculated ratios of the excitation energies of the ^157,159Tb nuclei are compared with the existing experimental data. The ratios of E2-transition probabilities and those of quadrupole moments of the above nuclei are calculated using parameters determined from the spectra of these nuclei. The text was submitted by the authors in English.