[en] This work is a contribution to the development of innovative concepts for fuel cladding in pressurized water nuclear reactors. This concept implies the insertion of rare earth (erbium and gadolinium) in the zirconium fuel cladding. The determination of phase equilibria in the systems is essential prior to the implementation of such a promising solution. This study consisted in an experimental determination of the erbium-zirconium phase diagram. For this, we used many different techniques in order to obtain diagram data such as solubility limits, solidus, liquidus or invariant temperatures. These data allowed us to present a new diagram, very different from the previous one available in the literature. We also assessed the diagram using the CALPHAD approach. In the gadolinium-zirconium system, we determined experimentally the solubility limits. Those limits had never been determined before, and the values we obtained showed a very good agreement with the experimental and assessed versions of the diagram. Because these alloys are subjected to oxygen diffusion throughout their life, we focused our attention on the erbium-oxygen-zirconium and gadolinium-oxygen-zirconium systems. The first system has been investigated experimentally. The alloys fabrication has been performed using powder metallurgy. In order to obtain pure raw materials, we fabricated powder from erbium and zirconium bulk metals using hydrogen absorption/desorption. The characterisation of the ternary pellets allowed the determination of two ternary isothermal sections at 800 and 1100 C. For the gadolinium-oxygen-zirconium system, we calculated the phase equilibria at temperatures ranging from 800 to 1100 C, using a homemade database compiled from literature assessments of the oxygen-zirconium, gadolinium-zirconium and gadolinia-zirconia systems. Finally, we determined the mechanical properties, in connexion with the microstructure, of industrial quality alloys in order to identify the influence of erbium content. We highlighted the hardening influence of erbium at 325 C. (author)

[en] Detailed information on the inner structure of the nucleon is provided by accurate data on the dependence of the nucleon form factors on momentum transfer q². Such data serve as a sensitive test for models of the nucleon. Particularly at low q² accurate data on the form factors are also needed for calculations of nuclear form factors. Whereas the proton form factors are known with excellent precision over a large range of q², data for the neutron are of much poorer quality due to the lack of a free neutron target. This is true for both the electric form factor, G_en, and to a somewhat lesser degree for the magnetic one, G_mn. With today's high duty factor, high current electron beam facilities like JLAB and MAMI, and the progress made in polarized beam and target technology, significant progress in this area is being made

[en] We determined the neutron magnetic form factor G_mn via a measurement of the ratio of cross sections D(e, e'n) and D(e, e'p). The absolute neutron detection efficiency of the detector is measured with high precision using tagged neutrons produced by H(n, p)n scattering of a high intensity neutron beam. In a first experiment we have demonstrated that with this method G_mn can be determined with high accuracy (''+'' 1.7%). (author)

[en] The ³He and ⁴He longitudinal and transverse response functions are determined from an analysis of the world data on quasi-elastic inclusive electron scattering. The corresponding Euclidean response functions are derived and compared to those calculated with Green's function Monte Carlo methods, using realistic interactions and currents. Large contributions associated with two-body currents are found, particularly in the ⁴He transverse response, in agreement with data. The contributions of two-body charge and current operators in the ³He, ⁴He, and ⁶Li response functions are also studied via sum-rule techniques. A semi-quantitative explanation for the observed systematics in the excess of transverse quasi-elastic strength, as function of mass number and momentum transfer, is provided. Finally, a number of model studies with simplified interactions, currents, and wave functions is carried out to elucidate the role played, in the full calculation, by tensor interactions and correlations

[en] The electromagnetic form factors of the nucleon are fundamental quantities relevant for an understanding of both nucleon and nuclear structure. Some of the form factors, in particular the neutron charge and magnetic form factors are known with comparatively poor accuracy due to both experimental systematical errors and the exploration of observable sensitive to uncertainties in the theoretical description. The proposed approaches for the future, using polarized electrons promise an order-of-magnitude type improvement. (author) 32 refs., 5 figs

[en] It is possible to measure the deep-inelastic spin-dependent structure functions g₁/sup p/(x) and g₁/sup n/(x) for the proton and neutron using internal polarized hydrogen, deuterium, and ³He targets of polarization 50% and thickness 10¹⁴ to 10¹⁵ cm^-2 and the 60 mA longitudinally polarized 30 GeV electron beam in the HERA electron storage ring. The measurement of the deep-inelastic spin-structure of both isospin states of the nucleon at the same kinematics and using the same apparatus allows the Bjorken sum rule to be experimentally checked. In addition, it uniquely constrains the spin distribution of the u and d quarks as a function of x in any model of the nucleon. Possible target and detector configurations are described and an estimate of the accuracy of such a measurement is presented

[en] We determine the Coulomb sum for ⁴He using the world data on ⁴He(e,e') and compare the results to calculations based on realistic interactions and including two-body components in the nuclear charge operator. We find good agreement between theory and experiment when using free-nucleon form factors. The apparent reduction of the in-medium G_Ep implied by IA-interpretation of the L/T-ratios measured in ⁴He(e,e'p) and ⁴He(e→,e'p→) is not confirmed

[en] The world data on inclusive quasi-elastic electron scattering have been used to determine the longitudinal and the transverse response functions of ¹²C, ⁴⁰Ca and ⁵⁶Fe. The resulting longitudinal response functions lack the quenching that has been one of the long-standing problems of nuclear physics. (orig.)

[en] We address the problem of including Coulomb distortion effects in inclusive quasielastic (e,e') reactions using an improved version of the effective momentum approximation. Arguments are given that a simple modification of the effective momentum approximation, which is no longer applicable in its original form in the case of highly charged nuclei, leads to very good results. A comparison of the improved effective momentum method with exact calculations is given. A critical remark concerns recent experiments with inclusive quasielastic positron scattering. (authors)

[en] We determined the neutron magnetic form factor G_mm via a measurement of the ratio of cross sections D(e, e'n) and D(e,e'p). The absolute neutron detection efficiency of the detector is measured with high precision using tagged neutrons produced by H(n,p)n scattering of a high intensity neutron beam. In a first experiment we have demonstrated that with this method G_m can be determined with high accuracy (±1.7%). copyright 1995 American Institute of Physics