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.

The refractive indices of non-chopped and chopped films of cryolite, MgF₂ and mixed cryolite-MgF₂, which is higher than the bulk value, measured using spectro-photometer, ellipsometer and Abeles method are observed to be higher than corres-ponding bulk values. Chopped films show a higher refractive index than non-chopped films. The electron diffraction study shows a more amorphous structure for the chopped films. The major part played by chop-time seems to be in increasing the initial minute’s-scale aging rather than settling of ad-atoms during chop-time. The observed dispersion curve shows that some unknown material other than water gives an important aging effect.

The effects of various ambients on the non-chopped and chopped films of cryolite, MgF₂ and mixed cryolite-MgF₂, as measured by ellipsometer, are reported. The moisture decreases the refractive index whereas an increase is observed in air and other ambients. In all the ambient-aging the chopped films show smaller changes (nearly half) in refractive index than non-chopped films. Aging seems to be due to three main processes, a long-term adsorption-like surface reaction and two short-term reactions.

A theory for clustering formation in nuclei and in heavy-ion collisions has been worked out in terms of the quantum-mechanical fragmentation process. Treating the mass fragmentation and relative separation coordinates as weakly coupled, the spontaneous cluster-decay of radioactive nuclei has been considered as a two-step process of clustering formation and tunnelling of the confining nuclear interaction barrier. This model has also been applied to “stable” nuclei, lighter than lead. The effects of adding more and more neutrons to collidingN =Z,A = 4n nuclei are studied for theα-clustering transfer phenomenon.