Measurement of the proton electric to magnetic form factor ratio from \vec ^1H(\vec e, e'p)

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared $Q^2$ from 0.15 to 0.65 (GeV/c)$^2$. Significantly improved results on the proton electric and magnetic form factors are obtained in combination with previous cross-section data on elastic electron-proton scattering in the same $Q^2$ region.Comment: 4 pages, 2 figures, submitted to PR

Cross sections and Rosenbluth separations in 1H(e, e'K+)Lambda up to Q2=2.35 GeV2

The kaon electroproduction reaction 1H(e,e'K+)Lambda was studied as a function of the virtual-photon four-momentum, Q2, total energy, W, and momentum transfer, t, for different values of the virtual- photon polarization parameter. Data were taken at electron beam energies ranging from 3.40 to 5.75 GeV. The center of mass cross section was determined for 21 kinematics corresponding to Q2 of 1.90 and 2.35 GeV2 and the longitudinal, sigmaL, and transverse, sigmaT, cross sections were separated using the Rosenbluth technique at fixed W and t. The separated cross sections reveal a flat energy dependence at forward kaon angles not satisfactorily described by existing electroproduction models. Influence of the kaon pole on the cross sections was investigated by adopting an off-shell form factor in the Regge model which better describes the observed energy dependence of sigmaT and sigmaL.Comment: 5 pages, 4 figures. Submitted to Physical Review C, Rapid Communication

M\uf6ssbauer study of Mg-Ni(Fe) alloys processed as materials for solid state hydrogen storage

Abstract Mg-Ni-Fe magnesium-rich intermetallic compounds were prepared following two distinct routes. A Mg88Ni11Fe1 sample (A) was prepared by melt spinning Mg-Ni-Fe pellets and then by high-energy ball milling for 6 h the obtained ribbons. A (MgH2)88Ni11Fe1 sample (B) was obtained by high-energy ball milling for 20 h a mixture ofNi, Fe and MgH2 powders in the due proportions. A SPEX8000 shaker mill with a 10 361 ball to powder ratio was used for milling in argon atmosphere. The samples were submitted to repeated hydrogen absorption/desorption cycles in a Sievert type gas-solid reaction controller at temperatures in the range 520\uf7590 K and a maximum pressure of 2.5 MPa during absorption. The samples were analysed before and after the hydrogen absorption/ desorption cycles by X-ray diffraction and M\uf6ssbauer spectroscopy. The results concerning the hydrogen storage properties of the studied compounds are discussed in connection with the micro-structural characteristics found by means of the used analytical techniques. The improved kinetics of hydrogen desorption for sample A, in comparison to sample B, has been ascribed to the different behaviour of iron atoms in the two cases, as proved by M\uf6ssbauer spectroscopy. In fact, iron results homogeneously distributed in sample A, partly at the Mg2Ni grain boundaries, with catalytic effect on the gas-solid reaction; in sample B, instead, iron is dispersed inside the hydride powder as metallic iron or superparamagnetic iron