[en] Gamma radiolysis of antibiotic tetracycline in aqueous solutions has been studied under various conditions. Anhydrotetracycline, a potential toxic substance, was identified as a major radiation degradation product formed under deoxygenated conditions mainly because of H atom attack on tetracycline. (author)

[en] Radiation induced polymerization of 3-sulfo propyl methacrylate (SPMA) in aqueous solution (10 wt%) has been studied by steady state and pulse radiolysis techniques. The effect of radiation characteristics such as irradiation dose, dose rate and the presence of crosslinking agent on the gel formation of SPMA monomer has been investigated. In N₂ -saturated solution, the gel formation doses for SPMA were found to be 70 and 258 Gy at dose rates of 1.2 and 5 kGy h^-1, respectively. The swelling ratio results showed that the gel obtained at a constant dose of 0.8 kGy dose swells ∼630 times of its dry weight at a dose rate of 5 kGy h^-1 whereas it is 394 times of its dry weight for the dose rate 1.2 kGy h^-1. The reactions of the primary radicals of water radiolysis such as e_aq^-, H-atom, OH radical, O^·-, and some oxidizing radicals like N₃^·, Cl₂^·-, SO₄^·- and reducing species like CO₂^·- with SPMA have been studied using pulse radiolysis technique. The results show that the reaction of e_aq^-, H-atom and OH radicals with SPMA are in the diffusion controlled limit with their respective bimolecular rate constant values being 8.6x10⁹, 2x10⁹ and 1.5x10¹⁰ dm³ mol^-1 s^-1. The radical anion, SPMA^·- , (λ_max=280 nm) is observed to undergo fast protonation forming H-adduct, SPMA--H^·, (λ_max=310 nm) with a pK_a value of 9.1. Cl₂^·- reacts with a bimolecular rate constant of 3.5x10⁷ dm³ mol^-1 s^-1 forming solute radical cation (λ_max=265 nm). One-electron oxidation and reduction potentials for SPMA/SPMA^·+ and SPMA/SPMA^·- couples are estimated to be more than +1.6 and less than -1.9 V, respectively

[en] Short communication

[en] Radiation induced effects on poly (p-sodium styrene sulphonate) (PSSS) of two molecular weights, namely 10⁶ and 70,000 in aqueous solution have been investigated by steady state and pulse radiolysis (PR) techniques. The reactions of primary radicals of water radiolysis such as OH radical, e_aq^-, H atom, some oxidizing radicals like N₃^·, Cl₂^·- and SO₄^·- and reducing species like CO₂^·-with PSSS have been investigated. The results indicate that the reactivity of these species towards PSSS is a function of molecular weight of PSSS. The absorption spectra of transient species produced when dilute aqueous solutions of PSSS of different molecular weights are subjected to pulse radiolysis have been compared. Rate constants for the reaction of OH radical and H atom with PSSS have been evaluated both by competition kinetics method and by direct observation of build up of transient species. The results indicate that OH radical and H atom react with PSSS in different ways. Near neutral pH, the OH radical reacts with substituted pendant aromatic ring of the PSSS to form an adduct, with a rate constant of 5.5x10⁸ and 1.1x10⁹ dm³ mol^-1 s^-1 for PSSS of molecular weights 10⁶ and 70,000, respectively. H atom on the other hand abstracts H atom from the PSSS backbone as well as forms an adduct by reacting with aromatic ring. The rate constant values for reaction of aqueous electron with PSSS were found to be 5x10⁷ dm³ mol^-1 s^-1 (M_w=10⁶) and 2.2x10⁸ dm³ mol^-1 s^-1 (M_w=70,000). The anion formed did not transfer electron to methyl viologen in the pH range of 6-10.5. The viscosity of the aqueous PSSS solution decreases with irradiation, up to doses of 1000 kGy indicating degradation of PSSS in this dose range. The PSSS of higher molecular weight is more prone to degradation. The chain scission is a function of dose rate, concentration of polymer and ambient of irradiation. At doses beyond ∼2500 kGy there is a sharp increase in viscosity of the PSSS solutions till the solutions set to a soft, sticky gel mass. The gelation dose (D_gel) is a function of molecular weight of the polymer and initial polymer concentration. In the presence of crosslinking agent like N,N-methylene bis acrylamide, the gelation was faster for PSSS of higher molecular weight. Gelation was most efficient for 20% (w/w) polymer concentration

[en] Radiation induced polymerization of sodium p-styrene sulphonate (SSS) in aqueous solution has been investigated by steady state and pulse radiolysis techniques. Effect of dose, dose rate, monomer concentration, pH and ambient conditions on polymerization was investigated. The reactions of primary radicals of water radiolysis such as OH radical, e^-_aq, H atom, O·^- and some oxidizing radicals like N·₃, Cl·^-₂,Br·^-₂, and reducing specie like CO·^-₂ with SSS have also been investigated. SSS reacts with OH radical with a rate constant of 5.9x10⁹ dm³ mol^-1s^-1 at pH 6.3. The results indicate that ∼83% of OH radicals undergo electron transfer reaction resulting in a cation radical species while remaining ∼17% react via addition reaction. The hydrated electron reacts with SSS with a rate constant 1.3x10¹⁰ dm³ mol^-1 s^-1 to form an anion that undergoes fast protonation to form H-adduct at pH 6.3. At high pH (>10) the anion is able to transfer electron to methyl vilogen and p-nitro aceto phenone (p-NAP) where as H-adduct is unable to transfer electron. At pH ∼1 H atom reaction with SSS is diffusion controlled with a rate constant of 5x10⁹ dm³ mol^-1 s^-1 and results in formation of H adduct. It was seen that anion reacts with solute an order faster than cation generated radiolytically indicating anionic initiation of polymerization of SSS. Molecular weight of the polymer formed by radiation polymerization, determined by viscosity measurement, are of the order of 10⁷ and higher molecular weight polymers are obtained at lower dose rates. In presence of a crosslinking agent gelation of polymer is much faster than the monomer and a polymer concentration ∼20% is most efficiently crosslinked. (author)

[en] Electron beam irradiation technique has been utilized to graft acrylic acid to cotton fabric in order to provide suitable functional groups that can subsequently react with urea or borax for making the fabric fire resistant. Thermal analytical technique such as, DSC and TG have been utilized to investigate the flame retardency characteristic of the grafted and treated fabric. The result shows that decay curve of exothermic peak due to combustion of cotton fabric in case of urea treated fabric at 330 degC becomes broad and shifts to higher temperature in DSC analysis as compared to pure cotton fabric and char residue in TG analysis is 20% in both the case. In borax treated fabric, char residue is found to be 40% in TG analysis and DSC profile is similar to that of urea treated fabric. (author)

[en] Fine metal particles with nanometer scale dimensions are of current interest due to their unusual properties that are different from their corresponding bulk materials. They are being explored for potential applications in optics, electronics, magnetics, catalyst, chemical sensing and biomedicine. A variety of methods are available in the literature for the synthesis of metal nanoparticles. The soft solution method involving the reduction of metal ion in the solution using reducing agent such as sodium borohydride, formaldehyde, trisodium citrate etc, are the most widely used. The ability of ionizing radiation to bring about ionization and excitation in the medium through which they travel results in the formation of reactive species which can be utilized to reduce metal ions into metal atoms to generate metal nanoparticles. The difference between gamma radiation method and soft solution method is that in the former the reducing species are generated in-situ whereas in later the reducing agent are incorporated into the system from an external source. A particular advantage of radiolysis method is that the reduction rate can be controlled by the selected dose rate unlike chemical method where the local concentration of reducing species is very high and cannot be controlled

[en] The reaction of N-hydroxy methyl acrylamide (NHMA) with the e_aq^-, ^·OH and ^·H radicals of water radiolysis were studied in dilute solutions using pulse radiolysis technique. The rate constants for the initiation reaction of NHMA monomer with hydrated electron (5.6x10⁹ dm³ mol^-1 s^-1), hydroxyl radical (3.4x10⁹ dm³ mol^-1 s^-1) and H atom (3.5x10⁹ dm³ mol^-1 s^-1) were found to be diffusion controlled. The reactions of some oxidizing radicals like N₃^·, SO₄^·- and reducing species like COO^·-, (CH₃)₂^·COH with NHMA have also been studied. The results show that oxidation and reduction potentials for NHMA/NHMA^·+ and NHMA/NHMA^·- couples are between 1.3 and 2.4 V and more than -1.9 V, respectively. Poly(NHMA) (PNHMA) hydrogels were synthesized by γ-irradiation and the conditions of synthesis such as total dose, dose rate, effects of oxygen and nitrogen, and concentration of monomer on gel formation characteristics were investigated. Maximum gel content (64%) has been achieved for 4 kGy dose (dose rate, 8k Gy h^-1) for air free 10% (w/v) monomer solution

[en] Radiation processing is an area of vigorous activity in today's India. With the indigenous expertise in ⁶⁰Co source and irradiator technology, potentially promising applications such as sustained drug delivery systems, vulcanization of natural rubber latex (RVNRL), and degradation of polytetrafluoroethylene (PTFE) are presently investigated. Over the last four years, technologies for RVNRL and PTFE degradation have been scaled up to pilot scale operations, while radiation polymerized polymer systems have been developed for controlled release of certain drugs. With the commissioning of the 2 MeV EB machine in late 1988, a few EB based processes have also been commercially exploited. The paper briefly reviews these and presents the significant results obtained. (author)

[en] Radiation processing is an area of vigorous activity in today's India. With the indigenous expertise in ⁶⁰Co source and irradiator technology, potentially promising applications such as sustained drug delivery systems, vulcanization of natural rubber latex (RVNRL), and degradation of polytetrafluoroethylne (PTFE) are presently investigated. Over the last four years, technologies for RVNRL and PTFE degradation have been scaled up to pilot scale operations, while radiation polymerized polymer systems have been developed for controlled release of certain drugs. With the commissioning of the 2 MeV EB machine in late 1988, a few EB based processes have also been commercially exploited. The paper briefly reviews these and presents the significant results obtained. (Author)