International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry最新文献

Thermoluminescence (TL) properties of curry powder, a salt containing spice mixture, and three different ground spices, viz. chilli, turmeric and pepper, were compared with TL of table salt. The spices other than curry powder, did not exhibit characteristic TL in the absence of salt. Therefore studies were initiated to develop a simple and reliable method using common salt for distinguishing irradiated spices (10 kGy) from unirradiated ones under normal conditions of storage. Common salt exhibited a characteristic TL glow at 170°C. However, when present in curry powder, the TL glow of salt showed a shift to 208°C. It was further observed that upon storage up to 6 months, the TL of irradiated curry powder retained about 10% of the original intensity and still could be distinguished from the untreated samples. From our results it is evident that common salt could be used as an indicator either internally or externally in small sachets for incorporating into prepacked spices.

The effect of additives on the grafting of a monomer, butylmethacrylate (BA), into simul (a soft wood) has been studied using ⁶⁰Co source at 3 Mrad. The enhancement of polymer loading (grafting) by the addition of minute amounts (1%) of oligomers (EA, PEA and UA) and of polyfunctional monomers (TMPTA, TPGDA and NVP) into simul + BA system has been further increased in the presence of acid and urea. The synergistic PL yields by acid addition cause substantial decrease of TS values of WPC; but urea increases both PL and TS values synergistically in these systems.

Addition of iron(III) sulfate (Fe₂(SO₄)₃) to the methyl viologen (MV²⁺)-poly(vinyl alcohol) (PVA) film dosimeter led to the induction dose (D_i) before appearance of blue-colored cation radical (MV^+.) and reduction of G-value of MV^+.. As a result, the measurable range for ionizing radiation (200 kV electron beam) was expanded to the higher dose >400 kGy, which was >25 times larger than that of base MV²⁺-PVA film (<14 kGy). In the MV²⁺-Fe₂(SO₄)₃-PVA film, iron(II) ion (Fe²⁺) was also accumulated without any induction dose. The Fe²⁺ still increased after D_i, with the G-value relatively smaller than that before D_i. Increase in pH ((pH)_i) of the source aqueous PVA solution, subjected to casting into films, led to the decrease in D_i and increase in G-value of MV^+. (G(MV^+.)). The ratio of initial concentration of Fe³⁺ ((C_Fe)_i) to D_i was apparently independent of (C_Fe)_i at given (pH)_i. These results suggest the mechanism that radiation-induced electrons in the PVA matrix reduce both MV²⁺ and Fe³⁺, and the resulting MV^+. successively reacts with neighboring Fe³⁺ to regenerate MV²⁺ in the initial stage of irradiation (within D_i). At the dose of D_i, such neighboring Fe³⁺ is consumed entirely and substantial formation of MV^+. can be observed.

In situ photolysis of aqueous solutions containing either 2&#x0301;-deoxyguanosine-5&#x0301;-phosphate or guanosine-2&#x0301;-phosphate and K₂S₂O₈ at pH<4 resulted in a resolved EPR-spectrum consisting of 40 equidistant peaks with a separation of 0.068 mT centered at g=2.0038. It originates from the guanosyl radical cation generated upon one-electron oxidation of the base moiety by SO^-•₄. In order to assist the assignment of the EPR-spectrum theoretical nitrogen and hydrogen hyperfine coupling constants were employed. They were obtained from spin density calculations based on the restricted open shell formalism at an ab initio level. For a conversion of calculated spin densities into coupling constants, calibration curves were constructed by applying a McConnell type approach to known nitrogen heterocyclic radical cations. For four different tautomers of the guanosyl radical cation theoretical spin densities and calibration curves were used to obtain coupling constants. They were applied in a simulation of the experimental EPR-spectrum. The simulation in combination with the calculated energies of the tautomers indicate that the EPR-spectrum originates from the guanosyl radical cation protonated at NI.

The paper reports on the development of the kinetics of radiation hydroxymethylation and hydroxypropylation chain processes relating to aliphatic saturated alcohols in the γ-radiolysis of the alcohol-unsaturated compound systems to give 1,2- and 1,4-diols respectively. These processes were simulated mathematically. The kinetic curves computed are in good agreement with the experimental dependences. The kinetic parameters of the processes, including the rate constants for the addition of α-hydroxyalkyl radicals from the saturated alcohols to the double bond of the unsaturated component, viz. formaldehyde or 2-propene-1-ol in the systems, were estimated. The constants (in dm³/mol·s) for the saturated alcohol-formaldehyde systems incorporating ethanol as the saturated alcohol were found to be (1.5±0.3)·10⁴ at 413 K and (2.1±0.5)·10⁴ at 443 K; incorporating 1-propanol-(6.0±1.3)·10³ at 413 K; for the saturated alcohol-2-propene-1-ol systems incorporating methanol, ethanol, 1- and 2-propanol-(2.5±0.3) ·10⁴, (6.5±0.9)·10⁴, (2.7±0.4)·10⁴ and (1.0±0.1)·10⁵, respectively, at 433 K.

Experimental results on increase of the probability of geminate ion pair separation into free ions caused by photoexcitation of trapped electrons in γ-irradiated 3-methylpentane glasses at 77 K are discussed. The increase is associated with injection of “hot” electrons in the medium. After thermalization the motion of the electrons is suggested to be governed by Smoluchowski's equation until stable trapped electron states occur. The dependence of the mean-square thermalization length on the electron energy in the interval 0.1–1.5 eV and the mean-square length (45 Å) of thermalized precursor of stable trapped electrons are estimated. It is concluded that electron localization precedes to total thermalization and is effective at electron energies <0.1 eV.

Reactivity of OH radicals, produced by γ-irradiation, in golden hamster embryo (GHE) cells and in phosphate-buffered saline (PBS) solutions containing nuclei of the GHE cells was studied at 77 and 111 K by ESR spectroscopy. Since OH radicals do not diffuse in frozen cells at 77 K, they do not react with organic substances, such as protein and DNA, in the cells at 77 K. The efficiency of production and trapping of OH radicals at high concentration of organic substances in cells are the same as that at low concentration. Thus OH radicals produced near the organic substances do not react with them, being trapped at 77 K. When GHE cells or PBS-nuclei solutions are irradiated by γ-rays at 77 K and then warmed to 111 K, OH radicals decay fast, while the amounts of organic radicals remain constant at this temperature. These results indicate that OH radicals do not react with organic substances in γ-irradiated cells during warming of the irradiated cells. Therefore it was concluded that OH radicals are not the main reactive species responsible for biological effects in γ-irradiated frozen cells.

The electron spin resonance (ESR) spectra of γ-irradiated potassium pyrosulfite single crystals have been investigated between 300 and 103 K temperature interval. The signals were attributed to three SO^-₃ and a SO^-₂ radicals, and found to be temperature dependent. The SO^-₃ radicals were found to be inequivalent. The presence of three SO^-₃ radicals is not consistent with the monoclinic structure of K₂S₂O₅ single crystal and this is attributed to any misadjustment of the orientations of SO^-₃ radicals to fit the crystal structure after irradiation. Elements of the g and hyperfine tensors of ³³S nuclei with natural abundance of 0.74% for SO^-₃ and SO^-₂ radicals were determined. For two SO^-₃ radicals, the g and hyperfine values in a plane perpendicular to a axis of the crystal were found to be equal below 193 K, while they are different at room temperature. This reversible effect can be attributed to structural phase transition.