Isospin Excitations Research Articles

Isospin and Symmetry Structurein 36Ar

The interacting boson model-3(IBM-3) has been used tostudy the isospin excitation states and electromagnetic transitions for36Ar nucleus. The mixed symmetry states and superdeformed band at lowspin are also analyzed. The theoretical calculations are in agreement withexperimental data, and the 36Ar is superdeformed rotational nucleusclose to the SU(3) limit. The present calculationsindicate that the 24+ state is the lowest mixed symmetrystate and the lowest isospin T = 1excitation state and at about 6.2 MeV, and the bandhead of superdeformedband is 02+ state.

Neutrino beams as a probe of the nuclear isospin and spin–isospin excitations

We explore the possibility of performing nuclear structure studies using low-energy neutrino beams. In particular, low-energy beta-beams and conventional sources (muon decay-at-rest) are considered. We present results on the total charged-current as well as flux-averaged cross sections associated to electron (anti-)neutrino scattering on oxygen, iron, molybdenum and lead, as typical examples. It is shown that by using neutrinos from low-energy beta-beams, information on forbidden states, in particular the spin-dipole, could be extracted.

Properties of the02+state and isospin excitation in theN=ZnucleusSe68

Band structure and electromagnetic transition properties of the low-lying states in the $N=Z$ $^{68}\mathrm{Se}$ nucleus were studied within the framework of interacting boson model 3. The isospin excitation states with $Tg{T}_{Z}$ are identified. The $M$1 and $E$2 matrix elements for low-lying states have been investigated and were used to identify the low-lying mixed symmetry states. Special attention is given to the occurrence of ${0}_{2}^{+}$ state, recently predicted by the projected shell-model (PSM) calculation. The present predicted spectrum for $^{68}\mathrm{Se}$ is close to the recent PSM results and confirms the results for the ${0}_{2}^{+}$ state. The calculated results are compared with available experimental data, and they are in general good agreement.

Isospin and symmetry structure in the f7/2 shell 44–48Ti isotopes

The interacting boson model 3 has been used to study the nuclear level structures and electromagnetic transition probabilities for 44–48Ti isotopes. This helps us to identify some low-lying mixed symmetry states. We have analysed the wavefunctions and given the symmetry labelling of the states. The analysis is consistent with the available data. The isospin excitation states with T > TZ are also studied, and comparison with experimental data is given.

Isospin and F -spin symmetry structure in low-lying levels of 48,50 Cr isotopes

The low-energy level structure and electromagnetic transitions of 48,50Cr nuclei have been studied using the interacting boson model with isospin (IBM-3). A sequence of isospin excitation bands with isospin T = Tz, Tz+1 and Tz+2 has been assigned and compared with available data. According to this study, the 2+3 and 2+2 states are the lowest mixed symmetry states in 48Cr and 50Cr, respectively. In particular, the present calculations suggest that a combination of isospin and F-spin excitation can explain the structure in these nuclei. The transition probabilities between the levels are analysed in terms of isoscalar and isovector decompositions which reveal the detailed nature of the energy levels. The results obtained are in good agreement with recent experimental data.

Quasiparticle random phase approximation based on the relativistic Hartree-Bogoliubov model. II. Nuclear spin and isospin excitations

The proton-neutron relativistic quasiparticle random-phase approximation (PN-RQRPA) is formulated in the canonical single-nucleon basis of the relativistic Hartree-Bogoliubov model, for an effective Lagrangian characterized by density-dependent meson-nucleon couplings. The model includes both the $T=1$ and $T=0$ pairing channels. Pair configurations formed from the fully or partially occupied states of positive energy in the Fermi sea, and the empty negative-energy states from the Dirac sea, are included in PN-RQRPA configuration space. The model is applied to the analysis of charge-exchange modes: isobaric analog resonances and Gamow-Teller resonances.

High-resolution determination of GT strength distributions relevant to the presupernova evolution using the (d,2He) reaction

Spin–isospin excitations of the medium-mass nucleus 58Co were studied using the (n,p)-type (d,2He) charge-exchange reaction at an incident energy Ed=170 MeV and small scattering angles. The achieved energy resolution of 130 keV, full width at half maximum, allowed the extraction of Gamow–Teller strength to 13 peaks at excitation energies lower than 4.1 MeV in the residual nucleus 58Co and is consistent with the results of a multipole-decomposition analysis. The identification of Gamow–Teller transitions is possible by comparison of the measured cross sections with DWBA calculations. The results are used to discuss the relevance of the Gamow–Teller strength distribution at low excitation energy with regard to electron-capture rates used in calculations for the final stage of a massive star.

Spin–isospin excitations and [formula omitted] half-lives of medium-mass deformed nuclei

A selfconsistent approach based on a deformed HF +BCS +QRPA method with density-dependent Skyrme forces is used to describe β + -decay properties in even–even deformed proton-rich nuclei. Residual spin–isospin forces are included in the particle–hole and particle–particle channels. The quasiparticle basis contains neutron–neutron and proton–proton pairing correlations in the BCS approach, while neutron–proton pairing interaction is treated as a residual force in QRPA. We discuss the sensitivity of Gamow–Teller strength distributions and β +/ EC half-lives to deformation, pairing and the strength of the particle–particle interaction. The dependence on deformation is also compared to that of spin M1 strength distributions.

Spin–isospin excitations and beta-decay of proton rich nuclei

Spin–isospin excitations and beta-decay of proton rich nuclei

Study of spin–isospin excitations in 11Be via the ( d, 2He) reaction at 270 MeV

Study of spin–isospin excitations in 11Be via the ( d, 2He) reaction at 270 MeV

Temperature dependence of superradiance intensity

Using the idea of exchange interaction in a system of two-level atoms participating in a superradiance process, we derive from first principles the superradiance Hamiltonian of such a system, which is found to be analogous to the Heisenberg Hamiltonian. We consistently calculate the coupling constant of the interaction that leads to the emergence of a superradiance state in the system. We also predict the existence of isospin excitations in the superradiance state, whose presence reduces the intensity of the corresponding superradiance pulse. Finally, we calculate the temperature dependence of the intensity of the superradiance pulse and find it be analogous to the Bloch T3/2-law for spin systems.

Symmetry Rearrangement of Spin and Isospin Symmetries and the Collective Modes in Nuclear Matter

A consistent theory of the spin and isospin excitations in an infinite nuclear system is formulated based on the Ward–Takahashi (W–T) relations among various many point Green's functions, which are derived from the requirement of the rotational invariance in spin and isospin space, SU(4). Collective modes are found to be six Nambu–Goldstone bosons, called spin, isospin, and spin–isospin waves, which appear as a result of the symmetry rearrangement of the SU(4) symmetry. The W–T relations are used to determine correlations among collective modes and to obtain a consistent expression for the static susceptibility beyond the random phase approximation. A consistent picture of the isovector collective excitations and their relationship to numerous experimental results is established. A partially conserved isovector current, analogous to a partially conserved axial current, in the symmetry rearrangement of isospin symmetry is established. This helps to define non-pertubatively the finite energy shift due to the explicit symmetry breaking terms.

Collective isospin excitations in nuclear matter droplets.

The isovector giant resonances in heavy nuclei are considered. These excitations correspond to a gapless Goldstone mode which comes along due to the broken symmetry in the isospin space, and can exhibit themselves in a nucleus where the numbers of neutrons and protons are not equal. These modes can be interpreted as weakly damped fluctuations of the transverse isospin components, which propagate through the nuclear matter. The dispersion law of such isospin waves is calculated on the basis of the Fermi-liquid theory as well as by means of the semiclassical variational method. The finite size of the nuclei leads to quantization of the spectra and results in a series of excited states. The number of long-living excited states is strongly affected by the Landau damping. The orthogonality relations and energy-weighted sum rule are formulated. The collective isospin modes of [sup 208]Pb and other heavy nuclei are computed.

Restoration of spin and isospin symmetry in the Skyrme model

I discuss an approximate application of the collective coordinate quantization method of Christ and Lee to the Skyrme model. The requirement that spin and isospin symmetry be maintained at the collective coordinate level necessitates the introduction of three vibrational degrees of freedom. Qualitatively, the vibrational degrees of freedom enable the magnitude of the pion field to vibrate uniformly between zero and the static classical solution of the Euler-Lagrange equations obtained by Adkins, Nappi and Witten. This effect is characterized by a vibrational frequency that sets the scale of vibrational excitations of the nucleon which are distinct from the spin and isospin excitations of the model. The lowest vibrational excitation of the nucleon is at 616 MeV for the choice of model parameters made by Adkins, Nappi and Witten. This is to be identified with the N ∗ (Roper) resonance. Since this approach requires three vibrational degrees of freedom at a collective level it is not surprising that this estimate for the N ∗ mass is larger than other approaches which introduce just one vibrational degree of freedom. I discuss some qualitative differences and similarities between this approach to the Skyrme model and the non-relativistic quark model and I also discuss some future applications.

RECENT ASPECTS OF THE NUCLEAR SPIN ISOSPIN RESPONSE FUNCTION

Various aspects of the nuclear response to spin isospin excitations are discussed, in particular the collective features of the 1p1h response and the response arising from the 2p2h excitations.

Antinucleon as a probe of nuclear spin and isospin excitations

Using two models for the antinucleon-nucleon ($\overline{\mathrm{N}}\mathrm{N}$) interaction, we obtain complex, energy dependent $\overline{\mathrm{N}}\mathrm{N}$ transition operators $t$ appropriate for ($\overline{\mathrm{N}}, {\overline{\mathrm{N}}}^{\ensuremath{'}}$) inelastic scattering studies on complex nuclei. It is shown that the spin-isospin dependence of the $\overline{\mathrm{N}}\mathrm{N}$ annihilation potential plays an important role in determining the dominant spin-isospin modes in the nuclear response. In particular, for the most realistic of our $\overline{\mathrm{N}}\mathrm{N}$ models, a large spin dependent component ${t}_{\ensuremath{\sigma}}$ is obtained, leading to the strong excitation of isoscalar spin-flip states; this term is suppressed in the corresponding NN $t$ matrix. The central spin and isospin independent term, ${t}_{0}^{c}$, is large for $\overline{\mathrm{N}}\mathrm{N}$, at all relevant momentum transfers $q$. At high $q$ the isoscalar spin-orbit (${t}_{0}^{\mathrm{LS}}$) and isovector tensor (${t}_{\ensuremath{\tau}}^{T}$) components are important. Cross section and analyzing power predictions for $\overline{\mathrm{N}}$ inelastic scattering as well as corrections due to energy and density dependence are discussed.