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The $\ensuremath{\alpha}$ ($^{4}\mathrm{He}$)-clustering structure is a common phenomenon in light nuclei due to the decreasing contribution of the mean field in few-body systems. In this work, we presented calculations of giant dipole resonance (GDR) excitations for two non-$\ensuremath{\alpha}$-conjugate light nuclei, namely $^{6}\mathrm{Li}$ and $^{9}\mathrm{Be}$, within a framework of an extended quantum molecular dynamics model. For $^{6}\mathrm{Li}$, we investigated the GDR spectra from the two-body clustering structure with $\ensuremath{\alpha}\phantom{\rule{4pt}{0ex}}+$ deuteron as well as the three-body structure with $\ensuremath{\alpha}+n+p$, and found that the major $\ensuremath{\alpha}$-clustering contribution on the GDR peak is located at around 31 MeV, while the resonance contributions between clusters, namely $\ensuremath{\alpha}$ and deuteron or $(n+p)$, are located on the lower energy side, which can be regarded as the pygmy dipole resonance (PDR). For $^{9}\mathrm{Be}$, a mixture configuration contribution for the chain-like structure and Borromean-like structure of the $\ensuremath{\alpha}\phantom{\rule{4pt}{0ex}}+\phantom{\rule{4pt}{0ex}}n\phantom{\rule{4pt}{0ex}}+\phantom{\rule{4pt}{0ex}}\ensuremath{\alpha}$ configuration can explain its GDR results.

Low-energy dipole (LED) excitations in $^{18}\mathrm{O}$ were investigated using a combination of the variation after $K$ projection in the framework of antisymmetrized molecular dynamics with $\ensuremath{\beta}$ constraint with the generator coordinate method. We obtained two LED states, namely, the ${1}_{1}^{\ensuremath{-}}$ state with a dominant shell-model structure and the ${1}_{2}^{\ensuremath{-}}$ state with a large $^{14}\mathrm{C}+\ensuremath{\alpha}$ cluster component. Both these states had significant toroidal dipole (TD) and compressive dipole (CD) strengths, indicating that the TD and CD modes are not separated but mixed in the LED excitations of $^{18}\mathrm{O}$. This is unlike the CD and TD modes for well-deformed nuclei such as $^{10}\mathrm{Be}$, where the CD and TD modes are generated as ${K}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$ and ${K}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ excitations, respectively, in a largely deformed state.

This paper shows that a dipole close to a subwavelength sphere can give rise to an anapole, namely the dipole-scatterer is a non-radiating system. This state can be achieved with either a dielectric (high refractive index) or metallic particle.

We investigate the effects of the long-range dynamic polarization (LRDP) potential, which consists of the Coulomb dipole excitation (CDE) potential and the long-range nuclear (LRN) potential, for the $^{11}\mathrm{Be}$ projectile on $^{64}\mathrm{Zn}$. To study these effects, we perform a ${\ensuremath{\chi}}^{2}$ analysis of an optical model including the LRDP potential as well as a conventional short-range nuclear (SRN) potential. To take these effects into account, we argue that both the CDE and LRN potentials are essential to explaining the experimental values of ${P}_{E}$, which is the ratio of the elastic scattering cross section to the Rutherford cross section. The Coulomb and nuclear parts of the LRDP potential are found to contribute to a strong absorption effect. Strong absorption occurs because the real part of the CDE and LRN potentials lowers the barrier, and the imaginary part of the CDE and LRN potentials removes the flux from the elastic channel in the $^{11}\mathrm{Be}+^{64}\mathrm{Zn}$ system. Finally, we extract the total reaction cross section ${\ensuremath{\sigma}}_{R}$ including the inelastic, breakup, and fusion cross sections. The contribution of the inelastic scattering by the first excited state at ${\ensuremath{\varepsilon}}_{\mathrm{x}}^{1\mathrm{st}}=0.32\phantom{\rule{4pt}{0ex}}\mathrm{MeV}\phantom{\rule{4pt}{0ex}}(1/{2}^{\ensuremath{-}})$ is found to be relatively large and cannot be ignored. In addition, our results are shown to agree quite well with the experimental breakup reaction cross section by using a fairly large radius parameter.

We investigate the effects of long-range dynamic polarization on elastic cross sections for heavy-ion collisions which comprise the Coulomb dipole excitation (CDE) potential and the long-range nuclear (LRN) potential. To study these effects, we perform a ${\ensuremath{\chi}}^{2}$ analysis for the elastic cross sections of $^{11}\mathrm{Li}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{208}\mathrm{Pb}$ and $^{6}\mathrm{He}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{208}\mathrm{Pb}$ systems using the long-range dynamic polarization potentials. For the CDE we formulate some empirical models to reproduce the experimental Coulomb dipole strength $B(E1)$ distribution and apply to the collision of $^{11}\mathrm{Li}$ and $^{6}\mathrm{He}$. But the CDE potential turns out to be not enough to explain the experimental data relevant to the nuclei. It leads us to additionally take the LRN potential peculiar to these halo nuclei into account. Our model, which was constructed by adding the CDE and LRN potentials to the conventional short-range nuclear potential corrected by the Coulomb interaction, provides a good description of the experimental data. In particular, the surface type is shown to be more reasonable rather than the volume type in the LRN potential.

For the $^{11}\mathrm{Li}+^{208}\mathrm{Pb}$ system, we find that the breakup process takes place from the forward angle or far distance region through the interaction distance which is obtained from ratios of elastic scattering cross sections to the Rutherford cross section. It is well known that the behavior of the $^{11}\mathrm{Li}+^{208}\mathrm{Pb}$ system is closely related to Coulomb dipole excitation effect. From the first ${\ensuremath{\chi}}^{2}$ analysis for the elastic cross section of the $^{9}\mathrm{Li}+^{208}\mathrm{Pb}$ system, we obtain the short-range potential of the $^{11}\mathrm{Li}+^{208}\mathrm{Pb}$ system by exploiting the optical model calculation for the Coulomb dipole excitation effect. To include the effect of the long-range interaction, we use a dynamic complex polarization potential including the Coulomb dipole potential and a long-range nuclear potential with Woods-Saxon form. Using the second ${\ensuremath{\chi}}^{2}$ analysis for the elastic cross section of the $^{11}\mathrm{Li}+^{208}\mathrm{Pb}$ system, we obtain the electric dipole transition probabilities $B(E1)$ which becomes 1.42 ${e}^{2}{\mathrm{fm}}^{2}$ and 1.41 ${e}^{2}{\mathrm{fm}}^{2}$ at ${E}_{\mathrm{c}.\mathrm{m}.}$ = 23.1 MeV and 28.3 MeV, respectively.

A recently proposed fluctuation analysis of resonant photon scattering spectra [J. Enders et al., Phys. Rev. Lett. 79, 2010 (1997)] is applied to the ${}^{157}\mathrm{Gd}(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ reaction. Evidence for unresolved strength in the experimental background is found which amounts to a total dipole excitation strength of $\ensuremath{\sum}g{\ensuremath{\Gamma}}_{0}^{\mathrm{red}}{=(30}_{\ensuremath{-}10}^{+6}){\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{M}\mathrm{e}\mathrm{V}}^{3}$ in the excitation energy range 2.5--4 MeV. Assuming a smooth variation of the $M1/E1$ strength ratio in the neighboring even-mass nuclei, the $M1$ part can be estimated to be ${B(M1)=(2.0}_{\ensuremath{-}0.7}^{+0.4})$ ${\ensuremath{\mu}}_{N}^{2}.$ This value is close to the expectation of sum rules. We discuss possible sources of errors which suggests that the obtained value represents a lower limit only.

A photon scattering experiment was performed on the $\ensuremath{\gamma}$-soft nucleus $^{134}\mathrm{Ba}$ with photon energies of ${E}_{\ensuremath{\gamma}}l4.1$. Around 3 MeV excitation energy a fragmented ${1}^{+}$ scissors mode as well as the ${({2}^{+}\ensuremath{\bigotimes}{3}^{\ensuremath{-}})}_{{1}^{\ensuremath{-}}}$ two-phonon dipole state were identified. The dipole excitation strengths were measured. The excitation strength of the scissors mode in this $\ensuremath{\gamma}$-soft nucleus is well reproduced by an empirical $M1$ sum rule that generalizes the "${\ensuremath{\delta}}^{2}$ law" to nuclei without axial symmetry. The IBM-2 describes the mixed-symmetry states in $^{134}\mathrm{Ba}$ and their decay pattern. A large $\frac{E2}{M1}$ mixing ratio for the ${1}^{+}$\ensuremath{\rightarrow}${2}_{1}^{+}$ decay of the scissors mode to the ${2}_{1}^{+}$ state is predicted by the IBM-2. The new result from $^{134}\mathrm{Ba}$ together with a similar previous observation in $^{196}\mathrm{Pt}$ corroborates the scissors mode as a typical excitation mode of $\ensuremath{\gamma}$-soft nuclei.

Resonant inelastic proton scattering experiments were carried out to investigate the {gamma} decay of the 1{sup {minus}} state at an excitation energy of around 3.5 MeV in the {ital N}=82 nuclei {sup 142}Nd and {sup 144}Sm. {gamma}-ray branching ratios were determined from {gamma}-proton coincidences in both nuclei. The newly observed {gamma} decay of the dipole excitation at 3225 keV in {sup 144}Sm to the one-phonon states, in particular the (1{sup {minus}}{r_arrow}3{sub 1}{sup {minus}}) {ital E}2 transition to the octupole phonon state, is the first direct proof of the two-phonon character of the 1{sup {minus}} state in any {ital N}=82 nucleus. {copyright} {ital 1996 The American Physical Society.}

Dipole excitations in highly excited energy regions of (6)He and (7)He nuclei were investigated via the ((7)Li,(7)Be) reaction with an incident energy of 65A MeV at forward scattering angles. The resonances at Q approximately equal to -30 MeV observed commonly for both (6)Li and (7)Li targets were found to be excited via both spin-flip and spin-nonflip transitions with DeltaL = 1. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be analogs of the dipole resonances of alpha clusters in the (6)Li and (7)Li nuclei.