Radiochromic gel dosemeter for three-dimensional dosimetry

A gel dosemeter in which ionising radiation causes a colour change was produced by modifying an existing Fricke gel system. This allows a more convenient preparation procedure and gives a better quality dosimetric system for three-dimensional (3-D) dose measurements. The role of three active components of the Ferrous sulphate Xylenol orange Gelatin (FXG) gel dosemeter is quantified with special consideration of their effect on system sensitivity and stability. The optimal composition was found to be 0.5 mM ferrous sulphate, 0.1 mM xylenol orange and 25 mM sulphuric acid. The dose response is linear in the range 0.1–30 Gy. The FXG sensitivity, derived from the gradient of the dose response curve, was found to be ΔA=0.084 cm⁻¹ Gy⁻¹, where A is the optical absorption coefficient at a wavelength of 585 nm, with reproducibility and 24 h stability of better than 5%.     

Photoelectrochemical response of methyl viologen cation radical incorporated in coated polysiloxane film

A photoelectrochemical response was found for a methyl viologen pendant polysiloxane film coated on an indium tin oxide (ITO) electrode dipped in an aqueous electrolyte solution containing O₂. Both the current direction (cathodic or anodic) and the extent of the photoresponse depended on the substitutional ratio of methyl viologen on the polymer chain. This behavior was not explained by simple photoinduced electron transfer from the excited cation radical of the methyl viologen to O₂. The mechanism is discussed for steady state O₂ and cation radical concentrations and with respect to O₂ permeability in the polysiloxane film.     

A glucose biosensor using methyl viologen redox mediator on carbon film electrodes

A new methyl viologen-mediated amperometric enzyme electrode sensitive to glucose has been developed using carbon film electrode substrates. Carbon film electrodes from resistors fabricated by pyrolytic deposition of carbon were modified by immobilization of glucose oxidase through cross-linking with glutaraldehyde in the presence of bovine serum albumin. The mediator, methyl viologen, was directly immobilised with the enzyme together with Nafion cation-exchange polymer. The electrochemistry of the glucose oxidase/methyl viologen modified electrode was investigated by cyclic voltammetry and by electrochemical impedance spectroscopy. The biosensor response to glucose was evaluated amperometrically; the detection limit was 20 μM, the linear range extended to 1.2 mM and the reproducibility of around 3%. When stored in phosphate buffer at 4 °C and used every day, the sensor showed good stability over more several weeks.     

ESR spectrometric characterization of the methyl viologen dosimeter in poly(vinyl alcohol) film

A dosimeter of poly(vinyl alcohol) (PVA) film containing methyl viologen dichloride (MV²⁺ (Cl^-)₂) was characterized by means of ESR and u.v. spectrometries. γ-irradiation of the MV²⁺-PVA dosimeter induced one-electron reduction of MV^2+· to thecation radical (MV⁺), thus giving rise to blue coloration. The resulting MV^+· showed an ESR signal with a g-factor of 2.0031. The yield of MV^+· at a given radiation dose was estimated from duplicate integral of the ESR first-derivative spectra by reference to 1,1'-diphenyl-2-picrylhydrazyl (DPPH). The yield of MV^+· thus estimated increased linearly with increasing the radiation dose up to about 1.4 Mrad. The ESR spectrometry of MV^+· showed a linear correlation with the u.v. spectrometric method reported previously.     

Synthesis and characterization of a symmetric bis(7-hydroxyflavylium) containing a methyl viologen bridge

A symmetric bis(flavylium) constituted by two 7-hydroxyflavylium moieties linked by a methylviologen bridge was synthesized. The thermodynamic and kinetics of the network of chemical reactions involving bis(flavylium) and the model compound 7-hydroxy-4'-methylflavylium was completely characterized by means of direct and reverse pH jumps (stopped flow) and flash photolysis. Both compounds follow the usual pH-dependent network of chemical reactions of flavylium derivatives. The equilibrium species of the model compound are the flavylium cation (acidic species) and the trans-chalcone (basic species) with an apparent pK'(a)=2.85. In the case of the bis(flavylium) it was possible to characterize by (1)H NMR spectroscopy three species with different degrees of isomerization: all flavylium, flavylium-trans-chalcone, and all trans-chalcone. Representation of the time-dependent mole fraction distribution of these three forms after a pH jump from equilibrated solutions of all-flavylium cation (lower pH values) to higher pH values, shows that formation of trans-chalcone is not completely stochastic (two independent isomerizations), the isomerization of one flavylium showing a small influence on the isomerization of the other. The radical of the methyl viologen bridge is formed upon reduction of the bis(trans-chalcone) with dithionite. The system is reversible after addition of an oxidant in spite of the occurrence of some decomposition.     

Styrylcyanine dye solutions for radiation dosimetry

The effect of -radiation on the electronic absorption spectra of the negatively solvatochromic dyestuff1, namely, 4-(4-N,N,-dimethylaminostyryl)-pyridinium methiodide in water and dimethylsulphoxide solvents is investigated. Ionizing radiation at different absorbed doses brought about gradual bleaching of aerated dye solutions. The -radiation-induced degradation and the consequent changes in the electronic absorption spectrum of dye 1 are discussed in the light of the theoretically calculated spectrum. The linear response range of dye1 in case of DMSO solution is wider than that in H₂O. The results demonstrate that the radiochromic dye solution offer dosimetry in the low dose range by means of visible spectrophotometric analysis.     

Micro determination of ascorbic acid using methyl viologen

A new simple and sensitive analytical spectrophotometric method is developed for the determination of ascorbic acid reduces methyl viologen to form a stable blue coloured free radical ion. This method has a sensitivity and lower limit detection of 0.1 μg ml⁻¹ of ascorbic acid (0.1 ppm) which is comparable to the flow injection analysis reported earlier. Beer's law is obeyed over the concentration range of 1.0-10 μg ml⁻¹ of ascorbic acid per 10 ml of the final solution (0.1-1.0 μg ml⁻¹) at 600 nm. The molar absorptivity and Sandell's sensitivity were found to be 1.5 × 10⁵ ± 100 l mol⁻¹ cm⁻¹ and 0.001 μg cm⁻², respectively. The method has been applied to the determination of ascorbic acid in food, pharmaceuticals and biological samples.     

Radiation grafting of methyl methacrylate on radiation crosslinked natural rubber film

Summary Grafting ofmethyl methacrylate (MMA) on radiation crosslinked natural rubber (NR) film has been investigated by mutual radiation grafting. The effect of experimental parameters like radiation dose, dose-rate, additives like acids and inorganic salts, solvents, monomer concentration, cross-linking density of the natural rubber film on the grafting extent has been studied.From the kinetic studies, a kinetic equation showing almost parabolic and linear dependence of grafting on concentration and dose rate, respectively, was deduced.Preliminary thermal stability studies of grafted films indicated that grafting of MMA does not enhance the thermal stability of NR.     

Photoinduced hydrogen evolution in an artificial system containing photosystem I, hydrogenase, methyl viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I, catalyst of hydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen.     

Photoinduced hydrogen evolution in an artificial system containing photosystem I,hydrogenase,methyl viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem Ⅰ, catalyst ofhydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transferfrom electron donors to proton was via a photoinduced reductive process of methyl viologen.2008 Dong Jin Qian. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Selective recognition of methyl viologen by an endo-functionalized naphthobox

Highly selective binding of structurally similar substrates is common for biomolecular recognition, but is often challenging to realize in synthetic hosts. Herein, we report highly selective binding of methyl viologen over other analogues by an endo-functionalized naphthobox. X-ray single crystal structure and Density Functional Theory (DFT) calculations revealed that the endo-functionalized groups in the cavity of the naphthobox is important for the high binding selectivity through the formation of multiple CH???N, CH???π, and π???π interactions with methyl viologen.     

Status of radiation processing dosimetry

Several milestones have marked the field of radiation processing dosimetry since IMRP 7. Among them are the IAEA symposium on High Dose Dosimetry for Radiation Processing and the international Workshops on Dosimetry for Radiation Processing organized by the ASTM.

Several standards have been or are being published by the ASTM in this field, both on dosimetry procedures and on the proper use of specific dosimeter systems. Several individuals are involved in this international cooperation which contribute significantly to the broader understanding of the role of dosimetry in radiation processing.

The importance of dosimetry is emphasized in the standards on radiation sterilization which are currently drafted by the European standards organization CEN and by the international standards organization ISO. In both standards, dosimetry plays key roles in characterization of the facility, in qualification of the process and in routine process control.

As a function of the work on the standards, several issues are now receiving major attention. These include traceability and uncertainty limits of the dose measurements, calibration procedures, environmental influence and combination of influence factors such as dose rate and temperature.

The increased attention to these factors have increased the demands on existing dosimeter systems, and rather than new dosimeters, the latest years have seen improvements on established dosimeters.     

Studies on radiation grafting of methyl methacrylate onto natural rubber for improving modulus of latex film

Methyl methacrylate (MMA) can be grafted onto natural rubber (NR) in latex by gamma irradiation for improving the mechanical properties of the dry films. Physical blending of MMA-grafted NR latex with radiation vulcanized natural rubber latex (RVNRL) or simultaneous radiation grafting and crosslinking are found to be useful techniques for improving the properties of latex films. Moduli of the films are improved with increasing MMA content; however, tensile strength is reduced. High modulus without much reduction in tensile strength can be achieved if the MMA content is 50–60 parts per hundred rubber.     

Spring open two-plus-two electron storage in a disulfide-strapped methyl viologen derivative

The synthesis of a disulfide-strapped viologen derivative is described starting from 4,4'-bipyridinyl-3,3'-diol. The first two one-electron reduction potentials, as determined by cyclic voltammetry, occur at E(1/2) = -0.03 V and E(1/2) = -0.16 V vs Ag/AgCl. This is accompanied by two more well separated one-electron reductions at E(1/2) = -1.26 V and E(1/2) = -1.54 V vs Ag/AgCl and the breaking of the disulfide bridge. To alleviate electrostatic repulsion between the two thiolate ions the molecular system must twist or "spring open" to accommodate the final two electrons.     

A thickness independent radiochromic film dosimetry system

A new radiochromic thin film dosimeter has been developed for use in radiation processing. The dosimeter's properties are similar to those of the commercially available FWT-60-00 Radiochromic Detectors with three key differences: 1) a lower sensitivity allows reading the optical density at the peak of the absorbtion spectrum (ca. 600 nm) for absorbed doses to over 50 kGy, 2) a radiation-insensitive dye additive allows for automatic thickness correction, and 3) another additive extends to higher doses the agreement between gamma and E-beam calibrations. The dosimeter is analyzed for its sensitivity, temperature and humidity dependencies, stability, reproducibility, and agreement of gamma and E-beam calibrations.     

Radiochromic Hydrogen-Bonded Organic Frameworks for X-ray Detection

Porous materials have been investigated as efficient photochromic platforms for detecting hazardous radiation, while the utilization of hydrogen bonded organic frameworks (HOFs) in this field has remained intact. Herein, two HOFs were synthesized through self-assembly of tetratopic viologen ligand and formic acid (PFC-25, PFC-26), as a new class of “all-organic” radiochromic smart material, opening a gate for HOFs in this field. PFC-26 is active upon both X-ray and UV irradiation, while PFC-25 is only active upon X-ray irradiation. The same building block yet different radiochromic behaviors of PFC-25 and PFC-26 allow us to gain a deep mechanistic understanding of the factors that control the detection specificity. Theoretical and experimental studies reveal that the degree of π-conjugation of viologen ligand is highly related to the threshold energy of triggering a charge transfer, therefore being a vital factor for the particularity of radiochromic materials. Thanks to its convenient processibility, nanoparticle size, and UV silence, PFC-25 can be further fabricated into a portable naked-eye sensor for X-ray detection, which shows obvious color change with the merits of high transmittance contrast, good sensitivity (reproducible dose threshold of 3.5 Gy), and excellent stability. The work exhibits the promising practical potentials of HOF materials in photochromic technology.     

Temperature dependence of the absorption spectrum of the methyl viologen cation radical and use of methyl viologen as a scavenger for estimating yields of the primary radicals in the radiolysis of high-temperature water

The absorption spectrum of the methyl viologen cation radical in an aqueous solution was measured as a function of temperature up to 200°C. The absorption coefficients at the two maxima, 605 and 395 nm, were both found to decrease with temperature, though the integral intensity of each of these bands remained almost constant. A pulse-radiolysis experiment, aimed at examining temperature dependence of the yield of hydrated electron, was made by using methyl viologen as a scavenger. The observed yield of the cation radical indicated that the G value of hydrated electron increases by about 28% upon temperature elevation from 20 to 200°C.     

Progress on standardization of electron beam dosimetry for radiation processing

The high dose standards and dissemination system of electron beams are being established at NIM. The graphite and/ or water calorimeters and liquid chemical dosimeter are to be accepted as standards. The transfer dosimeter selected are alanine/ESR dosimeter and radiochromic film (FWT - 60). Several kinds of radiochromic films, undyed cellulose triacetate, polyethylene and blue cellophane will be recommended as working dosimeter. A series of intercomparison studies are conducted between calorimeter and dichromate dosimeter. Agreement is found within 2%. Water calorimeters and dichromate dosimeters are used to make absolute dosimetric measurements of electron beams. These calibrated beams are then used to calibrate several types of dosimeters, such as alanine, radiochromic films, undyed and dyed polyethylene. Preliminary studies show that water calorimeter and dichromate dosimeter are reproducible and sufficiently accurate for electron beam calibration. The estimated overall uncertainty of the measurement is better than 5% at 95% confidence level.