Evolution of the dipole polarizability in the stable tin isotope chain

The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124 was extracted from inelastic proton scattering experiments at 295 MeV under very forward angles performed at RCNP. Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections.Comment: 10 pages, 6 figures, submitted to Phys. Lett.

Electric and magnetic dipole strength in 112,114,116,118,120,124Sn

Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295 MeV beam covering laboratory angles 0{\deg}-6{\deg} and excitation energies 6-22 MeV. Cross sections due to E1 and M1 excitations were extracted with a multipole decomposition analysis and then converted to reduced transition probabilities with the "virtual photon method" for E1 and the "unit cross section method" for M1 excitations, respectively. Including a theory-aided correction for the high excitation energy region not covered experimentally, the electric dipole polarizability was determined from the E1 strength distributions. Total photoabsorption cross sections derived from the E1 and M1 strength distributions show significant differences compared to those from previous ($\gamma$,xn) experiments in the energy region of the isocvector giant dipole resonance (IVGDR). The widths of the IVGDR deduced from the present data with a Lorentz parameterization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The E1 strengths below neutron threshold show fair agreement with results from ($\gamma$,$\gamma$') experiments on 112,116,120,124Sn in the energy region between 6 and 7 MeV. At higher excitation energies large differences are observed pointing to a different nature of the excited states with small ground state branching ratios. The isovector spin-M1 strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei.Comment: 32 pages, 23 figures, submitted to Phys. Rev.

Variable circular beam apertures

Two types of variable beam apertures used in the converted MP-Tandem at Munich are described. One of them uses eight sectors, four of which are insulated allowing beam position measurements. Due to its relatively small power dissipation this aperture is used only in the low energy region. The other type is an iris aperture designed for high power dissipation to be used in the terminal. The total beam current of this aperture can be measured. Both apertures can be completely closed and can therefore be used as Faraday cups. They are designed in UHV-techniques and can be baked at 200 °C

Variable circular beam apertures

Two types of variable beam apertures used in the converted MP-Tandem at Munich are described. One of them uses eight sectors, four of which are insulated allowing beam position measurements. Due to its relatively small power dissipation this aperture is used only in the low energy region. The other type is an iris aperture designed for high power dissipation to be used in the terminal. The total beam current of this aperture can be measured. Both apertures can be completely closed and can therefore be used as Faraday cups. They are designed in UHV-techniques and can be baked at 200 °C.Nous décrivons deux types de diaphragmes variables utilisés dans le MP Tandem converti de Munich. L'un d'entre eux utilise 8 secteurs, dont 4 sont isolés afin de permettre des mesures de position du faisceau. A cause de son pouvoir de dissipation relativement faible, ce diaphragme est utilisé uniquement dans la région de basse énergie. L'autre type est un diaphragme à iris conçu pour une dissipation de grande puissance, afin de pouvoir l'utiliser dans le terminal. Le courant total de ce diaphragme peut être mesuré. Les deux diaphragmes peuvent être complètement fermés et peuvent donc être utilisés comme des cages de Faraday. Ils sont conçus avec les techniques de l'ultra-vide et peuvent être réchauffés jusqu'à 200 °C