Analytical description of heavy ion potentials for collisions between nuclei of same shell

Using Skyrme energy density formalism, we present an analytical formula of ion-ion potential (including spin-density part) in terms of the masses of colliding nuclei. The parametrization of the spin-independent part of the ion-ion potential is based on the proximity theorem whereas the spin-dependent potential is parametrized in terms of “the masses of colliding nuclei and their associated particle strength”. The particle strength accounts for the number of valence particles outside the closed core. Adding Coulomb interaction, this parametrization of ion-ion potential introduces a great simplification for the calculation of fusion barriers and cross-sections analytically. Our parametrized potentials are in good agreement with other theoretical potentials and the fusion cross-sections calculated with this potential are in good agreement with experimental data. Received: 2 October 1997 / Revised version: 15 December 1997     

Interplay of wetting and phase separation at surfaces

We review our understanding of surface-directed spinodal decomposition (SDSD), i.e., the interplay of wetting and phase separation in an unstable AB mixture placed in contact with a wetting surface. In this context, we present results for two problems, viz., SDSD in a semi-infinite geometry with a completely wet surface; and SDSD in a thin-film geometry with partially wet surfaces.     

Surface-directed spinodal decomposition on a macroscopic scale in a nitrogen and carbon alloyed steel

Interactions with the macroscopic specimen surface can profoundly modify phase-separation processes. This has previously been observed in liquids and polymer films and is theoretically described by the theory of surface-directed spinodal decomposition (SDSD). Here we report first observations of SDSD in a metallic alloy on a macroscopic scale. The influence of the surface leads to the development of concentric domains extending over the whole 10 mm thick cylindrical steel specimen, due to long-range interactions via elastic stresses and long-range diffusion of the interstitial elements nitrogen and carbon.     

Evaluation of force constant ratio in the AlCu system

Band model calculations, using Mannheim's theory of nearest neighbour central force approximation in a cubic crystal, have been carried out to estimate the impurity-host to host-host coupling ratio λ'/λ in the AlCu system. The obtained value of 1.22 for λ′/λ suggests about 20 per cent stiffening of the impurity to host binding.     

Stark broadening parameters of Si I,Si II and Si III lines

Spectral lines emited by first three ionisation species of silicon were studyed in a wide range of plasma parameters. The silicon was present as an impurity in the argon plasma created in an electromagneticT tube. Four various condenser bank energies give the plasma in a range of temperatures 8700 to 16400°K and electron concentrations 2.95·10¹⁷ cm^?3to 5.6·10¹⁷ cm^?3. Measured line widths and shifts were compared with theories of Griem [1, 2] and Sahal Brechet [3, 10]. The agreement is reasonably good, the measured values are in general smaller than calculated ones.     

Stark width and shift dependence on the ionization potential

Analytic relations between the Stark widths and shifts and the ionization potential of the corresponding emitters have been found and are discussed.     

Re-estimation of force constant ratio in the Fe-Ni system

The temperature variation of second order Doppler shift of ⁵⁷Fe embedded as a dilute impurity in Ni host has been calculated by incorporating both the force constant change and the mass change at the site of the impurity. Comparison of the calculations with available measurements of second order Doppler shift gives definite evidence for the change of force constant λ′/λ. It appears that λ′/λ lies in the range 2·1–2·7 around the defect site. The analysis of the data in the high temperature limit further confirms this inference.     

Transverse momenta of secondaries from 200 GeV/c proton-nucleus interactions

A study of 100 interactions, produced by secondary particles from 200 GeV/c proton interactions in nuclear emulsions, has been made to estimate the transverse momenta of the secondary particles. The data have been analysed by different methods of energy estimation and the weighted average values ofp _t have been compared as estimated from various methods. An average value ofp _t equal to 0.38 ± 0.03 GeV/c, in proton-nucleus interactions at 200 GeV/c, has been obtained from the production mechanism method.