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Register a new userSplitting of the Dipole and Spin-Dipole Resonances
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Cross sections for the 90,92,94Zr(p,n) reactions were measured at energies of 79.2 and 119.4 MeV. A phenomenological model was developed to describe the variation with bombarding energy of the position of the L=1 peak observed in these and other (p,n) reactions. The model yields the splitting between the giant dipole and giant spin dipole resonances. Values of these splittings are obtained for isotopes of Zr and Sn and for 208Pb.
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High resolution experimental data has been obtained for the 40,42,44,48Ca(3He,t)Sc charge exchange reaction at 420 MeV beam energy, which favors the spin-isospin excitations. The measured angular distributions were analyzed for each state separately, and the relative spin dipole strength has been extracted for the first time. The low-lying spin-dipole strength distribution in 40Sc shows some interesting periodic gross feature. It resembles to a soft, dumped multi-phonon vibrational band with $hbaromega$= 1.8 MeV, which might be associated to pairing vibrations around $^{40}$Ca.
Resonance phenomena in solids generally fall into two distinct classes, electric and magnetic, driven, respectively, by the $E$ and $H$ components of the electromagnetic wave incident on the solid. The canonical examples of the two types of resonances are the electron cyclotron resonance (CR) and the electron paramagnetic resonance (EPR), originating from the electron orbital and spin degrees of freedom, respectively. The behavior becomes considerably more interesting (and more complicated) in the presence of the spin-orbital interaction. In this case, a more general type of resonance may occur, which is driven by the electric excitation mechanism and involves the spin degrees of freedom. Such electric-dipole spin resonance (EDSR) may occur at the spin excitation frequency or at a combination of the orbital and spin frequencies, spanning a wide bandwidth. The EDSR phenomenon, first predicted by Rashba (1960), has been probed experimentally in 3D solids with different crystal symmetries, as well as in low-dimensional systems (heterojunctions, inversion layers, dislocations and impurity states). Due to its electric dipole origin, the EDSR features a relatively high intensity, which may exceed by orders of magnitude the EPR intensity. This review summarizes the work on EDSR prior to 1991, laying out the theoretical framework and discussing different experimental systems in which the EDSR-related physics can be realized and explored.
Gamow-Teller (GT) and spin-dipole (SD) strength distributions of four doubly magic nuclei $^{48}$Ca, $^{90}$Zr, $^{132}$Sn and $^{208}$Pb are studied by the self-consistent Hartree-Fock plus random phase approximation (RPA) method. The Skyrme forces SAMi and SAMi-T without/with tensor interactions are adopted in our calculations. The calculated strengths are compared with available experimental data. The RPA results of GT and SD strengths of all four nuclei show fine agreement with observed GT and SD resonances in energy. A small GT peak below the main GT resonance is better described by the Skyrme interaction SAMi-T with the tensor terms. The quenching factors for GT and SD are extracted from the comparisons between RPA results and experimental strengths. It is pointed out that the quenching effect on experimental SD peaks is somewhat modest compared with that on GT peaks in the four nuclei.
Cross sections and polarization transfer observables in the $^{16}$O$(p,p)$ reactions at 392 MeV were measured at several angles between $theta_{lab}=$ 0$^circ$ and 14$^circ$. The non-spin-flip (${Delta}S=0$) and spin-flip (${Delta}S=1$) strengths in transitions to several discrete states and broad resonances in $^{16}$O were extracted using a model-independent method. The giant resonances in the energy region of $E_x=19-$27 MeV were found to be predominantly excited by ${Delta}L=1$ transitions. The strength distribution of spin-dipole transitions with ${Delta}S=1$ and ${Delta}L=1$ were deduced. The obtained distribution was compared with a recent shell model calculation. Experimental results are reasonably explained by distorted-wave impulse approximation calculations with the shell model wave functions.
In this work we present results of the dipole-dipole interactions between two neutrons, a neutron and a conducting wall, and a neutron between two walls. As input, we use dynamical electromagnetic dipole polarizabilities fitted to chiral EFT results up to the pion production threshold and at the onset of the Delta resonance. Our work can be relevant to the physics of confined ultracold neutrons inside bottles.
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