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In a recent paper it has been shown that a number of rare-earth elements have a definite deviation from axial symmetry, with the triaxiality angle $\ensuremath{\gamma}\ensuremath{\ge}8$ degrees and the ratios of the components of the inertia tensor in qualitative agreement with the irrotational model. Such results have been extracted from experimental data within the J-2 subspace, but scissors-mode resonances, which are most sensitive to the nuclear shape, were not included in the analysis. The irrotational and rigid inertia tensors have an opposite dependence on the triaxiality angle $\ensuremath{\gamma}$ and this affects in a striking way the fine structure of scissors-mode resonances.

The Two-Rotor Model predicts two levels above the Scissors Modes with degenerate intrinsic energy. They have $J^{\pi}= 0^+,2^+$ and are referred to as overtones. Their energy is below threshold for nucleon emission, which should make them observable. The $J^{\pi}=0^+$ overtone, that has the structure of an isovector breathing mode, has vanishing $E0$ amplitude so that cannot be directly excited, but it could be reached in the decay of the $J=2^+$ overtone. We discuss such a process and evaluate the $B(E2)$ strength, which, however, turns out to be very small., Comment: 4 pages, no figure

4 páginas.-- PACS number(s): 24.30.Cz, 24.30.Gd, 21.10.Re, 21.60.Ev, Scissors modes were predicted in the framework of the two-rotor model. This model has an intrinsic harmonic spectrum, so that the level above the scissors mode, the first overtone, has excitation energy twice that of the scissors mode. Because the latter is of the order of 3 MeV in the rare-earth region, the energy of the overtone is below threshold for nucleon emission, and its width should remain small enough for the overtone to be observable. We find that B(E2)↑overtone=1/64 θ02B(E2)↑scissors, where θ0 is the zero-point oscillation amplitude, which in the rare-earth region is of order 10−1.

In /sup 20/Ne, the isovector M2 strength distribution in the excitation region of E/sub x/ = 11--24 MeV was investigated by inelastic electron scattering. Two transitions to levels at E/sub x/ = 11.62 and 12.1 MeV were observed with strengths of B(M2,k)up-arrow = 64 +- 13 and 56 +- 13 ..mu../sub N//sup 2/fm/sup 2/, respectively. A comparison with the analogous (..pi../sup -/,..gamma..) reaction shows that orbital contributions are non-negligible in these transitions. The data are compared to model predictions.

The combined effect of the one pion exchange potential, the spin isospin dependent short range interaction, and the deformation on the M2 states in light deformed nuclei is studied in the framework of a semiclassical model which describes these magnetic states as longitudinal (along the symmetry axis) and transverse spin isospin oscillations. It is argued that these states might present quite distinctive properties depending on the shape of the nuclei and on the strength of the short range repulsive interaction, due to the anisotropic character of the one pion exchange potential, which gives most attraction to the longitudinal mode in oblate nuclei only.

The weak neutral axial current gives rise to coherent elastic scattering of neutrinos by nuclei with static spin-isospin order or pion condensation. The cross section is comparable to that for normal nuclei at much lower momentum transfer. This allows one to perform the experiment at values of the momentum transfer high enough for the recoil nucleus to be detectable and the contribution to the cross section from the vector current to be negligible.