Isovector monopole excitation energies

Using a hydrodynamical model whose parameters have been adjusted to fit the polarizability and excitation energy of the giant dipole nuclear resonance we predict excitation energies of the isovector monopole resonance. The predicted values are in good agreement with experimental data. The mass dependence of the excitation energy is strongly influenced by nuclear geometry.     

Damping of giant monopole resonances within a linearized Landau-Vlasov dynamics

Isoscalar monopole vibrations in spherical nuclei are studied within the Landau-Vlasov dynamics. Energy and strength of the giant monopole resonance (GMR) are well reproduced. The Landau damping of the monopole vibrations is analyzed. It is found that the local Fermi surface corresponding to the GMR is deformed. The collision integral is included within the relaxation time approximation. The found total width is too small to explain the observed one in heavy nuclei. Because the Landau damping is sensitive to the effective nuclear force the missing part of the width can be connected to certain properties of the latter.     

Isoscalar giant monopole resonance for drip-line and super heavy nuclei in the framework of relativistic mean field formalism with scaling calculation

We study the isoscalar giant monopole resonance for drip-lines and super heavy nuclei in the framework of relativistic mean field theory with a scaling approach. The well known extended Thomas-Fermi approximation in the nonlinear σ-ω model is used to estimate the giant monopole excitation energy for some selected light spherical nuclei starting from the region of proton to neutron drip-lines. The application is extended to the super heavy region for Z=114 and 120, which are predicted by several models as the next proton magic numbers beyond Z=82. We compared the excitation energy obtained by four successful force parameters NL1, NL3, NL3*, and FSUGold. The monopole energy decreases toward the proton and neutron drip-lines in an isotopic chain for lighter mass nuclei, in contrast to a monotonic decrease for super heavy isotopes. The maximum and minimum monopole excitation energies are obtained for nuclei with minimum and maximum isospin in an isotopic chain, respectively.     

Position and width of the monopole giant resonance in208Pb

The positions and widths of the monopole giant resonances in²⁰⁸Pb are calculated. The calculated widths include the effects of the single particle decay width and of the spreading width. We find the isoscalar resonance at E_res?13.0 MeV, while the isovector resonance is found at E_res?20.5 MeV. Due to the asymmetry of the resonance curves an unambiguous value for the widths can not be defined. Instead we present the form of the resonance curve in numerical form in table 1.     

First measurement of the giant monopole and quadrupole resonances in a short-lived nucleus: 56Ni

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the 56Ni unstable nucleus by inducing the 56Ni(d,d') reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3+/-0.5 MeV and 16.2+/-0.5 MeV, respectively. The corresponding angular distributions are extracted from 3 degrees to 7 degrees . A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.     

On direct proton decay of the isovector spin-flip giant monopole resonance

A semimicroscopic approach based on both the continuum-RPA method and a phenomenological treatment of the spreading effect is applied to describe the direct proton decay and gross properties of the charge-exchange isovector spin-flip giant monopole resonance. Calculation results are compared with the available experimental data. The text was submitted by the authors in English.     

Giant monopole resonances in the statistical model

The strength functions fore ⁺ e ^– pair decay of the isoscalar and isovector giant monopole resonances in highly excited nuclei are derived and used in a statistical model calculation of thee ⁺ e ^– pair energy spectrum from compound nuclear decay in¹¹⁰Sn following a fusion evaporation reaction. This result is then compared to thee ⁺ e ^– spectrum derived from internal pair decay of the giant dipole and giant quadrupole resonances. The computation shows that the pair decay from the excited-state GDR dominates the pair spectrum over the region of all giant resonances, exceedingL=0 transitions by at least a factor of ten. We also compute the angular correlations betweene ⁺ ande ^– for theL=0, L=1 andL=2 transitions and estimate their power to discriminate between the various multipolarities.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Correlating radii and electric monopole transitions of atomic nuclei

A systematic analysis of the spherical-to-deformed shape phase transition in even-even rare-earth nuclei from 58Ce to 74W is carried out in the framework of the interacting boson model. These results are then used to calculate nuclear radii and electric monopole (E0) transitions with the same effective operator. The influence of the hexadecapole degree of freedom (g boson) on the correlation between radii and E0 transitions thus established is discussed.     

Collisional damping of giant monopole and quadrupole resonances

Collisional damping widths of giant monopole and quadrupole excitations for ¹²⁰Sn and ²⁰⁸Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30 - 40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20 - 30% of the observed widths at zero temperature. Received: 9 January 2001 / Accepted: 29 March 2001     

Study of the fission decay of the isoscalar monopole resonance via the 238U(α, α′) reaction at 0°

The fission decay of ²³⁸U has been investigated using inelastic scattering of 120 MeV ga-particles to excite the ²³⁸U nucleus. Angular correlations of the fission fragments have been measured for excitation energies between 5.7 and 15.7 MeV in coincidence with inelastically scattered α-particles between 0 and 3°. The difference in yield for fission in coincidence with inelastically scattered α-particles between 0–1.35° and 1.35–3° was used to deduce the fission decay of the giant monopole resonance. It was found that in the fission decay channel (22 ± 5)% of the E0 EWSR strength is located between 8 and 15 MeV excitation energy. The distribution of the deduced monopole strength is in agreement with recent theoretical calculations predicting splitting of the giant monopole resonance in deformed nuclei.     

Relativistic and nonrelativistic calculations of the isoscalar monopole and dipole states

The study of the isoscalar giant monopole resonance (ISGMR) should allow extracting a value for the nuclear incompressibility coefficient K_∞. In this contribution, we review the most recent attempts along this line. While the nonrelativistic (Skyrme, Gogny) models predict K_∞ to be around 220–235 MeV, the values obtained from the relativistic calculations are significantly larger (250–270 MeV). We argue that the most plausible reason for this discrepancy lies in the different behavior of the symmetry energy in the two classes of models. We also discuss the role of the isoscalar giant dipole resonance (ISGDR). We conclude that a number of experimental ambiguities still prevent us from deducing K_∞ from the ISGDR with a comparable accuracy as from the ISGMR.     

Excitation and decay of the isovector giant monopole resonances via the 208Pb(3He,t p) reaction at 410 MeV

The excitation and subsequent proton decay of the isovector spin-flip giant monopole resonance (IVSGMR) is studied via the 208Pb(3He,t) reaction at 410 MeV. In the inclusive spectrum (60+/-5)% of the non-energy-weighted sum-rule strength for this 2 variant Planck's over 2h omega resonance was found in the region 29相似文献   

Decay of the isoscalar giant monopole resonance in 208Pb

The decay of the isoscalar giant monopole resonance (GMR) in ²⁰⁸Pb has been studied with the ²⁰⁸Pb(α, α'n)²⁰⁷Pb reaction at θ_α′ = 0°. Comparison of the experimental data with detailed statistical model calculations shows a good overall agreement for the decay of both the GMR and the underlying continuum. Interpreting small discrepancies between the calculations and data for the GMR as indications for the presence of pre-equilibrium decay we find a direct decay branch of the GMR ⩽ 10% and a pre-equilibrium decay branch ⩽ 30%.     

The strength of electric monopole transitions and the decay out of superdeformed bands

The strength of electric monopole (E0) transitions is related to differences in mean-square charge radii and differences in quadrupole deformation in nuclei. Estimates are made of E0 decay versus M1, E1, and E2 decay out of superdeformed bands. It is suggested that E0 decay may dominate, providing a (partial) answer to the superdeformed band “drainingr problem.     

Dynamical Thomas-Fermi theory for giant monopole resonances

Transition densities for giant monopole resonances of spherical nuclei are obtained from a linearized fluid dynamical approach. The same semiclassical energy functional is used to calculate self-consistently static and time dependent properties.     

Scaling- and antiscaling-type oscillations in isoscalar and isovector nuclear monopole vibrations

Isoscalar (T = 0) and isovector (T = 1) giant monopole resonances are studied using a localscale version of the ATDHF theory developed on the basis of a rigorous energy-density functional approach. Due to the strong coupling between the bulk and surface density vibrations, the monopole collective motion is split into four normal modes. Two of them, lower in energy, correspond to scaling-type density vibrations. The other two are of antiscaling-type in which the nuclear surface oscillates opposite in phase to the scaling-type vibrations. Excitation energies, transition densities, T = 0 and T = 1 energy weighted sum rules and other properties of breathing even-even nuclei are calculated using different Skyrme-type effective forces. The strong sensitivity of the antiscaling-type vibrations to the particular form of the approximate energy-density functionals is demonstrated.     

Systematics of the isoscalar giant monopole resonance from 60 MeV inelastic proton scattering

Evidence for an isoscalar giant monopole resonance is provided for seven nuclei with A ? 58. The resonance excitation energy is $\text{≈ 80 × A}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}\text{MeV}$. For nuclei with A ? 0, nearly 100% of the L = 0, T = 0 energy-weighted sum rule is depleted in the resonance, in agreement with earlier work on ²⁰⁸Pb and ¹⁴⁴Sm. Only ≈30% is found in ⁵⁸Ni, and no clear evidence is found for localized monopole strength in ⁴⁰Ca.