On the validity of the random phase approximation for pairing vibrations of closed shell nuclei

Energy loss measurements on solid xenon applying 51 keV-electrons are reported. The spectrum shows excitonic structure and a plasma loss. From the energy loss function —Im1/g3 optical constants are calculated by means of a Kramers-Kronig transform. They are compared with optical absorption spectra and found to be in good agreement. An appendix gives detailed information about the calculation of —Im 1/g3 from energy loss measurements.