Electroexcitation of giant resonances inN15

Abstract

The giant resonance region of $^{15}\mathrm{N}$ has been investigated by means of inelastic electron scattering in a momentum transfer range 0.36-1.25 ${\mathrm{fm}}^{\ensuremath{-}1}$. The data show a splitting of the dipole resonance into two main peaks at 22 and 25.5 MeV, with some structure around 20 MeV and strength extending down to 13 MeV. The structure from 19 to 30 MeV correlates well with radiative capture and photodisintegration data and is in qualitative agreement with shell model predictions of the isospin splitting of the giant dipole resonance. The data show considerable spin-flip $E1$ strength, which agrees well with the predictions of the generalized Goldhaber-Teller model. Additional structure found in the energy region from \ensuremath{\sim} 14 to \ensuremath{\sim} 19 MeV has been analyzed as a $C2\ensuremath{-}C1$ superposition. The $C2$ strength in the 14-18.5 MeV region exhausts up to 22% of the isoscalar energy-weighted sum rule (Helm model, $J=\frac{3}{2}$ assumed). The amount of $C2$ strength in the region from 18.5 to 30 MeV is negligible.NUCLEAR REACTIONS $^{15}\mathrm{N}(e, {e}^{\ensuremath{'}})$, $E=52\ensuremath{-}193.5$ MeV, $\ensuremath{\theta}=48\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}141\ifmmode^\circ\else\textdegree\fi{}$. Enriched gas target. Measured $\ensuremath{\sigma}({E}^{\ensuremath{'}}, \ensuremath{\theta})$. Deduced giant resonances differential form factors. Deduced $C1$, $C2$ strength distributions with Helm model. Compared differential $C1$ form factor to shell model calculations. Compared $C2$ strength to energy-weighted sum rule. Compared $E1$ strength to generalized Goldhaber-Teller model.