Isoscalar Giant Dipole Resonance Research Articles

Giant resonance research: present interests and future perspectives

In the last decade extensive work has been done to explore and understand various giant resonance phenomena. The research involved the study of the giant dipole resonance as a function of temperature and angular momentum, the study of compressional modes - the isoscalar giant monopole and dipole resonances - and the investigation of their microscopic structures, the study of the charge-exchange modes both in the β + and β − directions, the establishment of the existence of double-phonon giant resonances, in particular those of the isovector GDR and the isoscalar GQR, etc.. A review of some of these advances is discussed and possible future directions in view of the operating and/or planned radioactive nuclear beam facilities will be delineated.

Giant resonance research: present interests and future perspectives

In the last decade extensive work has been done to explore and understand various giant resonance phenomena. The research involved the study of the giant dipole resonance as a function of temperature and angular momentum, the study of compressional modes - the isoscalar giant monopole and dipole resonances - and the investigation of their microscopic structures, the study of the charge-exchange modes both in the β + and β − directions, the establishment of the existence of double-phonon giant resonances, in particular those of the isovector GDR and the isoscalar GQR, etc.. A review of some of these advances is discussed and possible future directions in view of the operating and/or planned radioactive nuclear beam facilities will be delineated.

Isoscalar giant dipole resonance for several nuclei with A ≥ 90

Isoscalar giant dipole resonance for several nuclei with A ≥ 90

The effect of deformation in the isoscalar giant dipole resonance

Background-free inelastic scattering spectra have been obtained for 144,148,150,152,154Sm with 386 MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the isoscalar giant dipole resonance. The strength distributions for isoscalar giant resonances have been extracted via a multipole decomposition analysis using angular distributions calculated in the framework of the density-dependent single-folding model. The effects of deformation are found to be different for the low- and high-excitation energy components of the isoscalar giant dipole resonance. Evidence has been obtained for the theoretically-predicted mixing between the isoscalar giant dipole resonance and the high energy octupole resonance.

The isoscalar giant dipole resonance: A status report

The current status of the experimental work on the Isoscalar Giant Dipole Resonance (ISGDR) is reviewed. Results are presented from recent measurements at RCNP, Osaka, using small-angle inelastic scattering of 400 MeV α particles, and the implications of these results on the determination of nuclear incompressibility are discussed.

Isoscalar giant dipole resonance for several nuclei with A ≥ 90

The giant resonance region in several nuclei in A ≥ 90 have been re-measured using 240 MeV α particle scattering with a detector provides that both horizontal and vertical angles. Slice analyses with multipole fits were performed and strength due to both low and high energy components of the isoscalar giant dipole resonance (ISGDR) was identified. E1 strengths for the high energy component corresponding to 70±15%,68±15% and 67±14% of the isoscalar E1 energy-weighted sum rule were identified, with centroid energies of 26.3±0.6 MeV, 24.7±0.6 MeV and 21.7±0.6 MeV for 90Zr, 144Sm and 208Pb, respectively. The centroid of the high energy component of the strength distribution is in closer agreement with the microscopic prediction generated using compressibilities obtained from the isoscalar giant monopole resonance data.

Theoretical understanding of the nuclear incompressibility: where do we stand?

The status of the theoretical research on the compressional modes of finite nuclei and the incompressibility K ∞ of nuclear matter, is reviewed. It is argued that the recent experimental data on the Isoscalar Giant Monopole Resonance (ISGMR) allow extracting the value of K ∞ with an uncertainity of about ± 12 MeV. Non-relativistic (Skyrme, Goguy) and relativistic mean field models predict for K ∞ values which are significantly different from one another, namely ≈ 220–235 and 250–270 MeV respectively. It is shown that the solution of this puzzle requires a better determination of the symmetry energy at, and around, saturation. The role played by the experimental data of the Isoscalar Giant Dipole Resonance (ISGDR) is also discussed.

Particle decay of the isoscalar giant dipole resonance in 208Pb

The direct particle decay of the isoscalar giant dipole resonance (ISGDR) has been studied in 208Pb using the (α, α′ p) and (α, α′ n) reactions at a bombarding energy of 200 MeV. The direct-decay channels of proton and neutron emissions were observed in coincidence with the scattered α-particles in order to study the population of proton-hole states in 207T1 and neutron-hole states in 207Pb. The results of the partial and total branching ratios allowed us to test recently performed continuum-RPA (CRPA) calculations for the ISGDR and thereby to learn about its microscopic structure.

Giant resonance research: present interests and future perspectives

In the last decade extensive work has been done to explore and understand various giant resonance phenomena. The research involved the study of the giant dipole resonance as a function of temperature and angular momentum, the study of compressional modes - the isoscalar giant monopole and dipole resonances - and the investigation of their microscopic structures, the study of the charge-exchange modes both in the β + and β − directions, the establishment of the existence of double-phonon giant resonances, in particular those of the isovector GDR and the isoscalar GQR, etc.. A review of some of these advances is discussed and possible future directions in view of the operating and/or planned radioactive nuclear beam facilities will be delineated.

Systematic study ofL⩽3giant resonances in Sm isotopes via multipole decomposition analysis

Background-free inelastic scattering spectra have been obtained for five Sm isotopes with $386\text{\ensuremath{-}}\text{MeV}$ $\ensuremath{\alpha}$ particles at forward angles (including $0\ifmmode^\circ\else\textdegree\fi{}$) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the $L\ensuremath{\leqslant}3$ isoscalar giant resonances have been extracted via a multipole decomposition analysis using angular distributions calculated in the framework of the density-dependent single-folding model. We observed a splitting of the giant monopole resonance because of its mixing with the giant quadrupole resonance. For the isoscalar giant dipole resonance, the observed effects of deformation are different for the low- and high-excitation-energy components. Evidence has been obtained for the theoretically predicted mixing between the isoscalar giant dipole resonance and the high energy octupole resonance.

Direct proton decay of the isoscalar giant dipole resonance

The direct proton decay of the isoscalar giant dipole resonance (ISGDR) has been studied in 208Pb using the (α,α′p) reaction at a bombarding energy of 200 MeV. Through observation of direct-decay protons from the ISGDR in coincidence with scattered α-particles, the population of proton–hole states in 207Tl was studied, allowing us to test recently performed continuum-RPA (CRPA) calculations for the ISGDR and thereby to learn about its microscopic structure. The energy and width of the ISGDR were also determined to be 22.1±0.3 MeV and 3.8±0.8 MeV, respectively. A new resonance of quadrupole character was observed at Ex=26.9±0.7 MeV with a width of 6.0±1.3 MeV.

Semimicroscopic description of basic properties of isoscalar monopole and dipole excitations in medium-mass spherical nuclei

A description of basic properties (strength function, transition density, probabilities of direct nucleonic decays) of isoscalar giant monopole (including an overtone) and dipole resonances in medium-mass spherical nuclei is proposed within a semimicroscopic approach. The approach relies on employing the random-phase approximation and involves taking exactly into account a single-particle continuum and some conditions of partial self-consistency and phenomenologically describing the coupling of states of the particle-hole type to multiquasiparticle configurations. The results of the calculations that were performed for 90Zr, 116,124Sn, 144Sm, and 208Pb nuclei are compared with available experimental data.

Current status of the nuclear matter incompressibility coefficient as deduced from data on compression modes

We review the current status of the nuclear matter incompressibility coefficient, K nm , as deduced from experimental data on excitation cross sections, σ( E), for the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant dipole resonance (ISGDR). We present results of microscopic calculations for the σ( E) of the ISGMR and the ISGDR, providing a resolution of the long standing problem concerning the value of K nm , deduced from the ISGDR data.

Isoscalar giant monopole and dipole resonances and the nuclear matter incompressibility coefficient

Isoscalar giant monopole and dipole resonances and the nuclear matter incompressibility coefficient

Self-consistent Hartree-Fock based random phase approximation and the spurious state mixing

We use a fully self-consistent Hartree$-$Fock (HF) based continuum random phase approximation (CRPA) to calculate strength functions $S(E)$ and transition densities $\rho_t(r)$ for isoscalar giant resonances with multipolarities $L = 0$, 1 and 2 in $^{80}Zr$ nucleus. In particular, we consider the effects of spurious state mixing (SSM) in the isoscalar giant dipole resonance (ISGDR) and extend the projection method to determine the mixing amplitude of spurious state so that properly normalized $S(E)$ and $\rho_t(r)$ having no contribution due to SSM can be obtained. For the calculation to be highly accurate we use a very fine radial mesh (0.04 fm) and zero smearing width in HF$-$CRPA calculations. We first use our most accurate results as a basis to establish the credibility of the projection method, employed to eliminate the SSM, and then to investigate the consequences of the common violation of self-consistency, in actual implementation of HF based CRPA and discretized RPA (DRPA), as often encountered in the published literature. The HF$-$DRPA calculations are carried out using a typical box size of 12 fm and a very large box of 72 fm, for different values of particle-hole energy cutoff ranging from 50 to 600 MeV.

Isoscalar giant dipole resonance in [formula omitted]Pb via inelastic α scattering at 400 MeV and nuclear incompressibility

The isoscalar giant dipole resonance (ISGDR) in 208Pb has been investigated with inelastic α-scattering of 400 MeV at extremely forward angles, including 0°. Energy spectra, virtually free from instrumental background, have been obtained and the ISGDR strength distribution has been extracted using a multipole-decomposition analysis (MDA). A difference-of-spectra approach yields the same ISGDR centroid energy as with MDA. These results lead to a value for nuclear incompressibility that is consistent for both the isoscalar dipole and monopole modes.

Compressional-mode giant resonances in deformed nuclei

Background-free inelastic scattering spectra have been obtained for the Sm isotopes with 400 MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the isoscalar giant resonances (L⩽3) have been extracted for the spherical nucleus 144Sm and the deformed nucleus 154Sm. We have observed that the effects of deformation are different for the low- and high-excitation-energy components of the isoscalar giant dipole resonance in 154Sm. Evidence for the theoretically predicted coupling between the isoscalar dipole resonance and the high-energy octupole resonance is reported.

Nuclear Equation of State and Compression Modes

The nuclear matter (N = Z and no Coulomb interaction) incompressibility coefficient, K nm , which is directly related to the curvature of the nuclear matter equation of state, is a very important physical quantity in the study of properties of nuclei, supernova collapse, neutron stars and heavy-ion collisions. We review the current status of K nm and the experimental and theoretical methods used to determine the value of K nm from the excitation crosssections σ(E) and the transition strength distributions S(E) of compression modes in nuclei. In particular, we will consider the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant dipole resonance (ISGDR) and provide a simple explanation to the long standing problem of the conflicting results obtained for K nm , deduced from experimental data on excitation cross sections for the ISGMR and data for the ISGDR.

The low-lying isoscalar giant dipole resonance

This short note is aimed to comment on the recently observed low component of the isoscalar giant dipole resonance in connection with the theoretical predictions made by microscopic and hydrodynamical models.

Isoscalar giant dipole resonance and nuclear matter incompressibility coefficient

We present results of microscopic calculations of the strength function, S(E), and alpha-particle excitation cross sections sigma(E) for the isoscalar giant dipole resonance (ISGDR). An accurate and a general method to eliminate the contributions of spurious state mixing is presented and used in the calculations. Our results provide a resolution to the long standing problem that the nuclear matter incompressibility coefficient, K, deduced from sigma(E) data for the ISGDR is significantly smaller than that deduced from data for the isoscalar giant monopole resonance (ISGMR).