The characteristic energy losses suffered by a 20 keV electron beam through CaF,, SrF,. and BaF, films have been measured with a magnetic spectrograph. Froin the energy loss function -I m cl, optical constants are calculated by means of Kramers-Kronig analysis in the 8 to 40 eV range and are conipared with the available reflectance data, especially those obtained with synchrotron radiation. The observed structure is tentatively explained for the three compounds, following a band model based upon symmetry considerations. The origin of the energy losses corresponding to the soft X-ray range is also briefly discussed.Les pertes d'bnergie caractkristiques subies par un faisceau d'klectrons de 20 keV B la traversBe de films de CaF,, SrF, et BaF, ont ktB mesurkes avec un spectrographe mag& tique. Les fonctions optiques ont Bt6 calculkes jusqu'a 40 eV par analyse de Kramers-Kronig a partir de la fonction -I m &-I, et sont comparkes aux mesures de rhflectiviti? trouvbes dans la litterature, particulibrement t i celles obtenues avec le rayonnement synchrotron. A partir d'un modble de structure de bande bask sur des considkrations de syrnBtrie, les spectres relatifs aux trois composBs sont interprBt8s. L'origine des pertes d'bnergie mises en Bvidence dans le domaine des rayons X mous est sommairement discuthe.

The characteristic energy losses suffered b y a 20 keV electron beam through thin films of some transition metals (Sc, Y, Zr, Hf) and of their oxides are measured using a magnetic spectrograph u p t o 50 eV. The energy loss function -1m 1/& and the complex diclectric constant are calculated. It is shown that the electron excitation spectra of metals contain two main contributions in this energy range: one due t o collective excitations of the conduction electrons, the other t o the excitation of inner p-electrons. In the case of oxides the spectra display three strong structures: there are probably two collective excitations of valence electrons followed by the excitation of inner p-electrons of the metal.Les pertes caractkristiques d'6nergie subies par u n faisceau d'6lectrons de 20 keV B la traverske de films minces de quelques m6taux de transitions placks en dkbut de s6rie (Sc, Y, Zr, Hf) e t de leurs oxydes ont 6t6 mesur6es avec un spectrographe magnetique jusqu'i 50 eV. La fonction -1m lie e t la eonstante dielectrique complexe sont calcul6es. On montre que le spectre des excitations 6lectroniques des mbtaux contient deux contributions principales dans le domaine d'6nergie considkrk : l'une due i l'excitation collective du gaz d'klectrons de conduction, l'autre B l'excitation des 6lectrons p. Dans le cas des oxydes, les spectres mettent en kvidence trois structures importantes: deux excitations collectives des 6lectrons de valence e t l'excitation des Blectrons p dn mktal.

The potential relationship between solar activity and changes in solar diameter remains the subject of debate and requires both models and measurements with sufficient precision over long periods of time. Using the PICARD instruments, we carried out precise measurements of variations in solar diameter during the rising phase of solar cycle 24. From new correction methods we found changes in PICARD space telescope solar radius amplitudes that were less than ±20 mas (i.e. ±14.5 km) for the years 2010-2011. Moreover, PICARD ground-based telescope solar radius amplitudes are smaller than ±50 mas from 2011 to 2014. Our observations could not find any direct link between solar activity and significant fluctuations in solar radius, considering that the variations, if they exist, are included within this range of values. Further, the contribution of solar radius fluctuations is low with regard to variations in total solar irradiance. Indeed, we find a small variation of the solar radius from space measurements with a typical periodicity of 129.5 days, with ±6.5 mas variation.