Excitation Of Giant Dipole Resonance Research Articles

Electromagnetic processes in silver isotopes

Peculiarities of electromagnetic interactions in silver isotopes are considered. Excited states of Ag isotopes are studied as a function of the mass number A = 95–117. Low-lying excited states reveal clear features that are specific for rotational spectra for the energies E < 4–5 MeV. In the energy domain above the nucleon separation threshold of 5–10 MeV, single-particle excited states overlap and produce a continuous spectrum. For energies E = 10–35 MeV, excitation of giant dipole resonance plays the most important role in Ag isotopes. Experimental data on the cross sections of photonuclear reactions in Ag isotopes are analyzed.

Giant dipole resonance in hot rotating nuclei

Over the last several decades, extensive experimental and theoretical work has been done on the giant dipole resonance (GDR) in excited nuclei covering a wide range of temperature (T), angular momentum (J) and nuclear mass. A reasonable stability of the GDR centroid energy and an increase of the GDR width with T (in the range $ \sim 1 - 3$ MeV) and J are the two well-established results. Some experiments have indicated the saturation of the GDR width at high T . The gradual disappearance of the GDR vibration at much higher T has been observed. Experiments on the Jacobi transition and the GDR built on superdeformed shapes at high rotational frequencies have been reported in a few cases. Theoretical calculations on the damping of the collective dipole vibration, characterised by the GDR width, have been carried out within various models such as the thermal shape fluctuation model and the phonon damping model. These models offer different interpretations of the variation of the GDR width with T and J and have met with varying degrees of success in explaining the experimental data. In this review, the present experimental and theoretical status in this field will be discussed along with the future outlook. The interesting phenomenon of the pre-equilibrium GDR excitation in nuclear reactions will be briefly addressed.

Estimate of production of medical isotopes by photo-neutron reaction at the Canadian Light Source

In contrast to conventional bremsstrahlung photon beam sources, laser backscatter photon sources at electron synchrotrons provide the capability to selectively tune photons to energies of interest. This feature, coupled with the ubiquitous giant dipole resonance excitations of atomic nuclei, promises a fertile method of nuclear isotope production. In this article, we present the results of simulations of production of the medical/industrial isotopes 196Au, 192Ir and 99Mo by (γ,n) reactions. We employ FLUKA Monte Carlo code along with the simulated photon flux for a beamline at the Canadian Light Source in conjunction with a CO2 laser system.

A new database (Digital Chart) of main GDR parameters

A new digital chart of the main parameters (energy, amplitude, width, some integrated values) of the giant dipole resonance (GDR) of atomic nuclei is developed. For many nuclei investigated in photonuclear reactions, the data are presented on the corresponding resonances appearing in cross sections of the reactions of main nucleus GDR excitation and decay channels, i.e., the total photoabsorption (γ, abs), reactions with formation of neutron (γ, xn), (γ, n), and (γ, 2n) and proton (γ, p), and others (with the formation of deuterons (γ, d), tritons (γ, t), and α-particles (γ, α)). The chart has a useful and convenient scaling tool: a digital zoom that makes navigation around the chart much easier and convenient. Through the table of search request processing results, the chart is connected with several other databases containing information on reactions in the cross section of which a GDR is observed, the target and final nuclei of these reactions, and a corresponding international bibliography database (DB) data sets.

Dynamic microscopic study of pre-equilibrium giant resonance excitation and fusion in the reactions132Sn+48Ca and124Sn+40Ca

We study pre-equilibrium giant dipole resonance (GDR) excitation and fusion in the neutron-rich system ${}^{132}$Sn $+$ ${}^{48}$Ca at energies near the Coulomb barrier, and we compare photon yields and total fusion cross sections to those of the stable system ${}^{124}$Sn $+$ ${}^{40}$Ca. The dynamic microscopic calculations are carried out on a three-dimensional lattice using both the time-dependent Hartree-Fock (TDHF) method and the density-constrained TDHF method. We demonstrate that the peak of the GDR excitation spectrum occurs at a substantially lower energy than expected for an equilibrated system, thus reflecting the very large prolate elongation of the dinuclear complex during the early stages of fusion. Our theoretical fusion cross sections for both systems agree reasonably well with recent data measured at the Holifield Radioactive Ion Beam Facility.

Multi-particle Photonuclear Reactions behind Giant Dipole Resonance

Experimental data on yields of multi-particle photonuclear reactions (involving the emission of up to seven neutrons from the nucleus involved) on 197 Au, 203;205 Tl, and 209 Bi nuclei in the region extending from the giant dipole resonance to an energy of 67.7 MeV are presented. These data are compared with the results of modern theoretical calculations that take into account both the excitation of a giant dipole resonance (GDR) in a nucleus and the photodisintegration of quasideutrons (QD) in it. By and large, experimental data conrm the results of theoretical calculations { that is, only upon taking simultaneously into account both alternative photodisintegration mechanisms (GDR excitation and QD photodisintegration) can one describe these experimental data. The contribution of QD photodisintegration grows with increasing photon energy and neutron multiplicity and becomes dominant for reactions with the emission of not less than ve neutrons from the nucleus being considered.

Photodisintegration of heavy nuclei in the energy region above the giant dipole resonance

Experimental data on yields of multiparticle photonuclear reactions (involving the emission of up to seven neutrons from the nucleus involved) on 197Au, 203,205Tl, and 209Bi nuclei in the region extending from the giant dipole resonance to an energy of 67.7 MeV are presented. These data are compared with the results of modern theoretical calculations that take into account both the excitation of a giant dipole resonance (GDR) in a nucleus and the photodisintegration of quasideutrons (QD) in it. By and large, experimental data confirm the results of theoretical calculations—that is, only upon taking simultaneously into account both alternative photodisintegration mechanisms (GDR excitation and QD photodisintegration) can one describe these experimental data. The contribution of QD photodisintegration grows with increasing photon energy and neutron multiplicity and becomes dominant for reactions involving the emission of not less than five neutrons from the nucleus being considered. The integrated cross sections for the processes in question were estimated on the basis of simultaneously employing experimental yields of multinucleon photonuclear reactions and the respective cross-section shapes calculated theoretically.

Relativistic Coulomb excitation of the giant dipole resonance in nuclei: How to calculate transition probabilities without invoking the Liénard-Wiechert relativistic scalar and vector potentials

The conclusions extracted from a recent study of the excitation of giant dipole resonances in nuclei at relativistic bombarding energies open the way for a further simplification of the problem. It consists in the elimination of the relativistic scalar and vector electromagnetic potentials and the familiar numerical difficulties associated with their presence in the calculation scheme. The inherent advantage of a reformulation of the problem of relativistic Coulomb excitation of giant dipole resonances along these lines is discussed.

Theory of multiple giant dipole resonance excitation

Theory of multiple giant dipole resonance excitation

Isospin structure of one- and two-phonon giant dipole resonance excitations

Isospin is included in the description of the Coulomb excitation of multiple giant isovector dipole resonances. In the excitation of even-even nuclei, a relevant portion of the excitation strength is shown to be associated with ${1}^{+}$ two-phonon states, which tends to be hindered or completely suppressed in calculations in which the isospin degree of freedom is not considered. We find that the excitation cross section is strongly dependent on the ground state isospin.

Time scales of multiple giant dipole resonance excitation and decay

A semiclassical description of multiple giant resonance excitation and decay that incorporates incoherent fluctuation contributions of the Brink-Axel type is developed. Numerical calculations show that the incoherent contributions are important at low to intermediate bombarding energies.

Improved limit on the branching ratio of μ−→ e+ conversion on titanium

The SINDRUM II spectrometer at PSI is used in searches for μ→ e conversion in muonic atoms. Here we report on a search for the charge-changing μ −→ e + conversion on titanium. The measurements yielded the new upper limits Γ( μ −Ti → e +Ca GS )/ Γ( μ −Ti capture)<1.7×10 −12 (90% CL) for the ground state transition and Γ( μ −Ti → e +Ca GDR )/ Γ( μ −Ti capture)<3.6×10 −11 (90% CL) for a giant dipole resonance excitation with both a mean energy and a width of 20 MeV. These results improve on our previous best limits by a factor of 2.5.

GDR excitation by isoscalar probes: a means to determine the neutron-skin thickness

Inelastic scattering of a-particles can excite the isovector giant dipole resonance (GDR) via the Coulomb interaction. In spite of their isoscalar nature alpha-particles carl also excite the GDR via the nuclear interaction due to the difference in the radii of the neutron and proton density distributions. The absolute cross section to excite the GDR in inelastic alpha-scattering is therefore a measure of this radial difference, the so-called neutron-skin thickness. Furthermore, since the GDR strength distribution has a centroid energy which depends on the nuclear radius, these studies, when performed in deformed nuclei, can measure the neutron-skin thickness along both the short and the long axes independently. Results of an experiment performed at KVI at E-alpha = 120 MeV and small scattering angles, including 0 degrees, to determine the neutron-skin thickness in Pb-208, Sn-116, Sn-124, and the deformed Nd-150 are discussed and compared to earlier measurements and theoretical predictions. Future improvements in the experimental set-up are also discussed.

On the giant dipole resonance excitations in very hot nuclei

We discuss some of the ingredients necessary in the study of the excitation of the Giant Dipole Resonance in very hot nuclei.

Multiple excitation of giant dipole resonances in relativistic heavy ion collisions.

The relativistic excitation of the double giant dipole resonance in $^{136}\mathrm{Xe}$ has been calculated, describing the resonance as a harmonic vibration of the mean field, damped through its coupling to doorway states. While the predictions associated with the one-phonon states provide an overall account of the experimental findings, the calculated cross section for the two-phonon states is much smaller than that extracted from the involved analysis of the data. The experimental elucidation of this discrepancy seems essential for assessing the validity of the standard picture of giant resonances.

Multi-phonon excitation of giant dipole resonances

Electromagnetic excitations of single and multi-phonon giant resonances occur with large cross sections in energetic heavy-ion collisions. First results on the double isovector giant dipole resonance obtained at SIS are summarized.

Electromagnetic dissociation of relativistic heavy-ions in emulsion

We report the results on the electromagnetic dissociation of 14.5A GeV28Si and 200A GeV16O projectiles in nuclear emulsion. The overall charge changing production cross sections are determined experimentally and are found to agree reasonably well with those computed theoretically. The relative rate as a function of decay energy for various reaction channels are parameterized in terms of an exponential function. Majority of the events in the most prominent decay modes can be attributed to the excitation of giant dipole resonances. Multiplicity distributions of α particles emerged from nuclear as well as electromagnetic interactions are also investigated.

Proton and deuteron radiative capture to A = 13 nuclei

Differential capture 12C(p, γ) 13N and 11B(d, γ) 13C cross sections have been measured in the excitation energy region between 20 and 45 MeV in 13N and 25 and 42 MeV in 13C. Angular distributions are given for the pγ channel at each energy, while the dγ excitation function has been measured at 60°. The pγ 0 data show, besides a direct capture term, the excitation of giant dipole resonances based on excited states of the compound nucleus. The main feature of the deuteron capture cross section can be understood in terms of a mechanism in which the proton-neutron pair is captured in the same single particle configuration by the 11B core.

Relativistic coulomb excitation of giant resonances in the hydrodynamical model

We investigate the Coulomb excitation of giant dipole resonances in relativistic heavy-ion collisions using a macroscopic hydrodynamical model for the harmonic vibrations of the nuclear fluid. The motion is treated as a combination of the Goldhaber-Teller displacement mode and the Steinwedel-Jensen acoustic mode, and the restoring forces are calculated using the droplet model. This model is used as input to study the characteristics of multiple excitation of giant dipole resonances in nuclei. Possibile signatures for the existence of such states are also discussed quantitatively.

Proton and deuteron radiative capture in light nuclei

Differential capture 16 O( p, γ x) 17 F and 15 N( d, γ x) 17 O cross sections have been measured at excitation energies between 17 and 41 MeV in 17F and 26 and 39 MeV in 17O at several angles in the 35°–135° interval. The (p, γ o) data show, besides a direct capture term, the excitation of giant dipole resonances based on excited states having a probable 2p-1h structure. The main features of the deuteron capture cross section can be understood in terms of a semidirect mechanism with the two nucleons captured in the same single-particle configuration.