In the world scenario understanding radiation chemistry in the time domain of hundreds of nano seconds to milliseconds started with the inception of pulse radiolysis technique. In India also research on time-resolved radiation chemistry started after the linear accelerator based pulse radiolysis system was set up in 1986 in Chemistry Division of Bhabha Atomic Research Centre. In the initial years the basic understanding of the mechanisms underlying redox reactions of organic compounds was the main area of research. The basic thrust was in characterizing the transients, determination of redox potentials, rate constants, ionic equilibria, etc.One important current area of research is the study of antioxidant properties of natural and synthetic organic molecules in relation to the mechanistic path and products formed. Most of these compounds are either established drugs/antioxidants or new ones. Some of the compounds studied are gingeroids, eurcuminoids, meroterpene (bakuchiol), fiavonoids, melatonine, sesamol, etc. Results from our research group conclusively demonstrated that besides phenolic groups, the moieties like β-diketone, allylic side chain and unsaturation in the α-β position of an organic molecule can play a crucial role in the antioxidant action. Moreover, folic acid, a B-group vitamin, was first time coined as an antioxidant.Another important area of research is that of metal nanoparticles. Formation, characterization and studies on the catalytic properties of these particles in solid as well as in solution were initiated in early nineties. Metal nanoparticles of Au, Ag, Pd, Pt, Co, Ni, Cu, Cd, Tl and bimetallic particles of Cu-Cd, Ag-Tl were prepared in aqueous solutions, microemulsions, as self-supporting powder, in polymer matrix and dispersed on the surface of A12O3 and SiO2 using radiolytic, photolytic and chemical reduction methods. The steps involved in the formation of clusters from precursor metal ions were detected as a function of time. The nanoparticles are characterized by their absorption spectra, XRD and TEM. The effect of intense laser beams on the morphology of the particles has also been demonstrated. Moreover, the effect of supporting material and the size of the particles on catalytic properties have also been studied.In the application side, radiation-induced polymerisation studies have led to the development of PVC-based hydrogels for treatment of bum injuries and monsooning of coffee beans, etc. Electron beam as well as γ-irradiation has been applied for several industrial products and study on wood polymer composites and rubber.We are in the process of setting up a laser based accelerator facility in our research centre, for studying sub-picosecond ultrafast phenomena.
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