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- Author or Editor: S. Kapoor x
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Abstract
Hydrogen peroxide yields in air-saturated methanol-water mixtures with methanol: water volume ratios varying from 1
99 to 1000, produced by60Co gamma-irradiation boith at room temperature and at 77 K have been determined. At room temperature, G(H2O2) values are almost constant over the entire range of methanol: water ratios. However, for irradiations at 77 K, G(H2O2) values increase with increasing methanol concentration up to the volume ratio of 982.
Abstract
Using the pulse radiolysis technique, the oxidation of the biological protein bovine serum albumin (BSA) by the species N 3 . , CCl3O 2 . , OH and Br 2 .– has been studied in aqueous solution. The repair of the N 3 . oxidation by ascorbic acid and the effect of denaturing the protein on this repair has also been studied. The oxidation of Br 2 .– seems to follow a different course from that of the other oxidizing agents suggesting the possibility of positive hole mobility in this protein. The repair by ascorbic acid is found more effective in the case of denatured protein. The rate constants for the reaction of Br 2 – and N 3 . are lower, in general, in the case of the denatured protein as compared with the undenatured BSA both at pH 6.9 and pH 10.7, suggesting that the convoluted structure of the protein plays a part in the process.
Abstract
The use of beams of heavy ions such as carbon, neon and argon for radiation therapy has the advantage that they have a very sharp Bragg maximum. When the Bragg peak coincide with the tumour location, it is possible to deposit the bulk of the energy of the ion in the region occupied by the malignancy. However, the concentration of ions and free radicals will be very high in the Bragg peak region which has not received the attention it deserves. So mutual recombination of these species will be very high. It is therefore necessary to assess the extent of these radical-radical recombinations at very high LET values. Spur diffusion model calculations have been made for high energy argon ions using water as a medium. For comparison, calculations have been done for proton tracks. It has been shown that in the Bragg peak region of argon ions even very high concentrations of scavengers have very little effect on radical-radical interactions. The implication is that when LET values are very high, practically all the radicals undegro recombination with each other. In order to explain the observed lethality of high LET radiation, it is suggested that the hydrogen peroxide formed also contribute to the killing of cells. In addition, the decomposition of H2O2 will contribute oxygen. This may be one of the reasons why high LET radiation shows strong lethality to hypoxic cells.
Abstract
Mixtures of methanol and isopropanol in a ratio (v/v) varying from 9
1 to 19 have been gamma-irradiated at 77 K and relative yields of trapped electrons have been measured. The reactivity of the trapped electrons towards acetone and uranyl nitrate has been studied at various methanol isopropanol ratios. On the basis of the results, an attempt has been made to assess the relative importance of the reaction of the electron with the solute prior to trapping with respect to the tunnelling reaction of the trapped electron with the solute.
Abstract
Trapped electron (e T – ) reactivity in methanol-isopropanol glasses irradiated at 77 K has been studied as a function of trap-depth, the variation in the trap depth being achieved by varying the methanol:isopropanol ratio. Benzyl chloride and carbon disulfide have been used as scavengers. In the case of the glasses containing benzyl chloride, the observed yield of the benzyl radical has been correlated with the trapping efficiency of the matrix. The data has been interpreted with the aim of assessing the relative importance of tunnelling in the scavenging of electrons in low temperature glassy matrices.
Abstract
Four litres of Am solution containing 81.5 mg/l Am and 0.6 mg/l Pu could be purified by a two-step procedure involving solvent extraction and extraction chromatography with trilaurylamine. The final product contained a maximum concentration of 
9 
g/l Pu.
For a graphG, the switched graphS
v
(G) ofG at a vertexv is the graph obtained fromG by deleting the edges ofG incident withv and adding the edges of
incident withv. Properties of graphs whereS
v
(G) ≅G or
are studied. This concept is extended to the partial complementS
H
(G) where H
. The investigation here centers around the existence of setsH for whichS
H
(G) ≅ G. A parameter is introduced which measures how near a graph is to being self-complementary.
Studies on energetic compounds
IV. Thermal explosion of ring-substituted arylammonium perchlorates
Thermal and explosion characteristics of ring(mono) substituted arylammonium perchlorates (RSAP) are studied by DTA, impact and friction sensitivity measurements. Exothermic decomposition temperature (T d) from DTA curves and impact sensitivity data (h 50%) were found to be linearly related to the Hammett substituent constant (σ+,σ−) andpK a values of the corresponding arylamines. A reaction scheme, based on the formation of reaction intermediates during decomposition and explosion, accounting for the products, is proposed which, involves proton transfer as the rate determining process and evolution of ammonia. It seems that oxidation-reduction reactions between the arylamine/substituted benzene and HClO4 or its decomposition products cause explosion.
Abstract
The tail-end purification of Am from Pu loading effluents in 7.5M HNO3 containing 
160 mg l–1 Am and 1.2 mg l–1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO3+0.05M NaNO2, the Pu level is brought down to 31.2 
g l–1. When the acidity was reduced to 4.2M HNO3, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO3+0.05M NaNO2 gave Am samples without any detectable amounts of Pu. The recovery of Am was 90% by the first procedure and 98% by the second one.
