Dose rate dependence of cellulose triacetate dosimeter and radiochromic film dosimeter

The doses of γ-rays and electron beams were evaluated by Fricke dosimetry and the responses of cellulose triacetate dosimeter (CTA) and radiochromic film dosimeter (RCF) to the two types of radiations were compared to investigate their dose rate dependence. Both the change in absorbance at 280 nm of CTA and that in absorbance at 510 nm of RCF caused by γ-irradiation were larger than those by electron-irradiation, when the dosimeters were irradiated to the same dose. The results in this study suggest that the responses of CTA and RCF are dependent upon dose rate.     

Mobility of some ions produced by tritium betas

The aqueous solution of coumarin has been studied spectrophotometrically as a -ray dosimeter and effects of temperature and light conditions on the stability of response during post-irradiation storage have been studied. Post-irradiation storage at room temperature in dark showed that after a very small increase in absorbance within the first 6 d, the response of the dosimeter was stable up to 42 d. At lower temperature (–15 °C), there was some decrease in absorbance within the first 24 h followed by a stable response up to 35 d. For post-irradiation storage at higher temperatures (40, 60 °C) the dosimeter, apart from some initial increase in absorbance, showed a nearly stable response up to 25 d. The effect of different light conditions during post-irradiation storage has also been studied. When stored in fluorescent light the response was almost stable from 6 d till about 40 d. In diffuse sunlight, the response was stable up to about 35 d at 360 nm and 370 nm but showed a somewhat unstable behavior at 347 nm. The dosimetric solutions were unstable when exposed to direct sunlight.     

Muscle and plastic equivalent glass dosimeter for high-dose dosimetry

The alkali-silicate glass dosimeter is made up of 66.8% SiO₂, 31.2% Li₂O, 2% K₂O. It is nearly colourless before irradiation and then takes on an amber colour with increasing doses of gamma-radiation. This colouration is represented by the appearance of broad absorption bands at 405 nm and 600 nm wavelengths. The change in absorbance is linear with the absorbed dose in the range 0.1–4.5 kGy, when measured at its 405 nm absorption band maximum. This glass dosimeter simulates low-z plastics and muscle tissue in terms of gamma-ray absorption properties over broad radiation spectra (0.1 MeV to 10 MeV).     

Characterization of aqueous solution of cresol red as food irradiation dosimeter

Dilute aqueous solution of cresol red has been evaluated spectrophotometrically as possible gamma rays dosimeter. A 0.10 mM solution of cresol red was irradiated by gamma rays using a cobalt-60 radiation source. The absorbance spectra of the unirradiated and irradiated solutions were recorded using double beam scanning spectrophotometer. The absorbance of the solution before and after irradiation was measured at 434 nm (λ_max) as well as at other wavelengths (415, 448 and 470 nm). Various parameters, such as Absorbance (A), ΔA, %A, -log A and log A_o/A_i were plotted against radiation dose, in order to check the response of cresol red solution and its possible use as chemical dosimeter. The response plots of A, ΔA, and %A versus absorbed dose showed that the solution can be used as a radiation dosimeter in a dose range up to 0.82 kGy. Using response plots of -log A and log A_o/A_i, the useful dose range can be extended up to 1.65 kGy; which are useful dose ranges for food irradiation applications. Stability studies of cresol red solution at different light and temperature conditions for pre- and post-irradiated storage of the dosimetric solutions suggested that aqueous solution of cresol red is highly stable in dark, under fluorescence light and at room temperature up to 150 days     

Effects of humidity and temperature during irradiation on the response of blue PMMA dosimeter

Effects of relative humidity conditions in the irradiation chamber and of temperature of the chamber on the response of 3 mm thick light blue poly (methyl methacrylate) sheets have been studied. The response was measured spectrophotometrically at 402, 450, 596 and 612 nm. The response of the dosimeter is independent of the relative humidity (12–97%) during irradiation if the response is measured within 24 h of irradiation. If the response is measured after longer storage time, the absorbance at 402 and 450 nm increases significantly. At these two wavelengths the response of the dosimeter is also independent of the temperature of the irradiation chamber in the range of 0 to 40 °C. However, at higher temperatures (60, 80 °C), the response is not uniform.     

Post-irradiation stability of response of an aqueous coumarin dosimeter

Aqueous solution of coumarin (-benzopyrone) has been evaluated spectrophotometrically as a -ray dosimeter. In the present study measurements have been made at peak wavelength of 347 nm as well as at two other wavelengths (i. e. 360 and 370 nm). The response of the dosimeter with respect to absorbed dose is linear in the range of 0.05 to 0.5 kGy when absorption measurements are made at 347 nm. However, this dose range can be increased up to 0.8 kGy if analyzed at longer wavelengths of 360 and 370 nm. Postirradiation stability at room temperature in the dark show that the response increases gradually till 6 d. Afterwards the response is almost stabilized up to 42 d at all the wavelengths studied.     

Characterization of aqueous rose bengal dye solution for the measurement of low doses of gamma radiation

Aqueous solution of rose bengal dye has been studied spectrophotometrically as a gamma-ray dosimeter for the measurement of low doses of radiation. The useful dose range was found to be from 50 to 1000 Gy when the measurements were made at 549 nm. The effects of temperature and light conditions on the stability of response during post-irradiation storage were also investigated. When stored in dark at room temperature, the dosimetric solutions showed a stable response up to 22 days. The storage of irradiated solutions in diffused sunlight showed a stable response only up to 6 days. When exposed to direct sunlight, very prominent and fast bleaching of dye solution occurred. At low storage temperature (ca. 11 °C), dosimetric response was found to be stable up to 22 days while at higher temperature (ca. 30 °C), the response of dosimetric solution was stable only up to 6 days. The rose bengal aqueous solution showed promising characteristics as a low dose radiation dosimeter when stored at lower temperatures (<25 °C) in dark.     

Application of clear polymethylmethacrylate dosimeter Radix W to a few MeV electron in radiation processing

Characteristics of clear PMMA dosimeter (Radix W) were studied for electron irradiation and compared with the response for gamma irradiation. The dose–response curves were nearly linear up to 30 kGy and become sublinear at higher doses. The radiation-induced absorbance was reduced with 6% within 4 h after irradiation. Dose comparisons were performed for 2, 3, 4 and 5 MeV electron irradiation using cellulose triacetate dosimeter (CTA) (FTR-125) and Radix W dosimeters which were independently calibrated for 2 MeV electrons and ⁶⁰Co gamma-rays using calorimeter and ionizing chamber, respectively. The doses estimated by CTA and Radix W were different by about 20%. The magnitude of this difference was, however, independent of electron energy.     

Characteristics study of clear polymethylmethacrylate dosimeter,Radix W,in several kGy range

Basic characteristics of Radix W, a commercially available undyed polymethylmethacrylate (PMMA) dosimeter conventionally used by readout at 320 nm, were studied in the dose range of 0.5–8 kGy, for its wide application especially for the evaluation of the sterilization dose and the quality assurance of food irradiation. The characteristics of dose response, the effect of irradiation temperature, and its stability after irradiation were examined over candidate readout wavelengths of 270–320 nm. The dose response readout at shorter wavelength is higher than that at longer wavelength, and 280 nm is the suitable readout wavelength for measurement of dose range of 0.5–8 kGy. The post-irradiation stability of dose response for 6 kGy is less than 1% within 24 h after irradiation at an irradiation temperature of 20 °C. Dose response is higher with temperature at irradiation temperatures in the range of −40 to 20 °C.     

Stability of response of the ferrous-cupric sulfate dosimeter at different temperatures

Aqueous solution of ferrous-cupric sulfate has been evaluated spectrophotometrically as radiation dosimeter and post-irradiation stability at different storage temperatures has been studied. The response curve drawn at a peak wavelength of 304 nm shows a linear response of up to 7 kGy. However, with proper calibration, the system can be used up to 14 kGy. At room temperature (ca. 25 °C) in the dark, the irradiated solution showed stable response up to about 12 h, followed by a small decrease in response up to 20 d. Post-irradiation storage at lower temperature (10 °C) shows no significant change in absorbance over a storage period of 6 d. However, for storage at higher temperature (40 °C) the dosimeter showed a stable response only up to a few hours and at longer storage times the response of the dosimeter increased.     

Optical waveguide dosimetry for gamma-radiation in the dose range 10-1 − 104 Gy

Two types of liquid-core optical waveguide (OWG) dosimeters are commercially available for dosimetry in the irradiation of foods and other products. “Opti-chromic” type FWT-70-40M has a useful range of about 10-10⁴ Gy and type FWT-70–83M about 10²−10⁴ Gy. 5 Within the limits of random uncertainty of the reading of the absorbed dose (±5%, 1σ), the response to γ-radiation is independent of dose rate over the range 10^-1−10⁴ Gy/h, when measured at the peak of the spectrum [absorption band maximum (600 nm wavelength)]. The response curve is linear with dose up to ≈10³ Gy, but is non-linear at higher doses, where the readings are made away from the absorption peak (656nm). Both dosimeter types when measured at 600 nm are temperature dependent over the temperatures ranges of -40 to 60°C during irradiation. The dosimeters cannot be used when exposed to temperatures > 60°C because of bubble formation and loss of light propagation. At doses < 10³ Gy (at600 nm), the dosimeters are stable (in terms of dose readings) for several months following irradiation, but at doses ≈ 10⁴ kGy (at 656 nm), they show a gradual absorbance increase (error in dose interpretation), over post-irradiation storage periods longer than 1 month. A special, sensitive OWG dosimeter (50-cm coil), designed for doses down to 10^-1 Gy, shows a linear response up to at least 15 Gy, a temperature dependence of response only at temperatures below ≈ 20°C, and no dose-rate dependence.     

Effect of post-irradiation thermal treatments on the stability of gamma-irradiated glass dosimeter

A commercial window glass has been investigated as a routine high dose dosimeter for gamma irradiation. The irradiated samples showed rapid fading at room temperature immediately after irradiation. This short-term rapid fading was followed by a slow fading at long-term. This strong initial fading is a problem for dosimetry purposes. However, when the dosimeter is measured at the same time interval after irradiation, it maintains proportionality to dose. Calibration curves have to be used for different time intervals after irradiation. In order to improve post-irradiation stability dosimeters were submitted to different post-irradiation thermal treatments from (−20) up to 150 °C. After that, optical absorbance measurements were carried out up to 2 months at room temperature. The heating at 150 °C for 20 min was found to be the most suitable procedure for the removal of unstable entities responsible for the initial rapid fading. Due to these heat treatments, variation of response was found almost negligible 24 h after irradiation for several months. Calibration curves demonstrated the applicability of this glass as routine dosimeter in the dose range of 0.5–90 kGy.     

Spectrophotometric determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic acid in pharmaceuticals

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV ⁺) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10⁴ L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.     

Hydrogen-bonding molecular ruler surfactants as probes of specific solvation at liquid/liquid interfaces

Resonance-enhanced, second harmonic generation (SHG) is used to measure the electronic structure of solutes sensitive to specific solvation adsorbed to liquid/liquid and liquid/solid interfaces. Here, specific solvation refers to solvent–solute interactions that are directional and localized. N-methyl-p-methoxyaniline (NMMA) is a solute whose first allowed electronic transition wavelength remains almost constant (∼315 nm) in non-hydrogen-bonding solvents regardless of solvent polarity. However, in hydrogen-bond-accepting solvents such as dimethylsulfoxide, NMMA’s absorbance shifts to longer wavelengths (320 nm), whereas in hydrogen-bond-donating solvents (e.g., water), the absorbance shifts to shorter wavelengths (∼300 nm). SHG experiments show that at alkane/silica interfaces, surface silanol groups serve as moderately strong hydrogen-bond donors as evidenced by NMMA’s absorbance of 307 nm. At the carbon tetrachloride/water interface, NMMA absorbance also shifts to slightly shorter wavelengths (298 nm) implying that water molecules at this liquid/liquid interface are donating strong hydrogen bonds to the adsorbed NMMA solutes. In contrast, experiments using newly developed molecular ruler surfactants with NMMA as a model hydrophobic solute and a hydrophilic, cationic headgroup imply that, as NMMA migrates across an aqueous/alkane interface, it carries with it water that functions as a hydrogen-bond-accepting partner.     

琼脂糖基类丁二炔凝胶剂量计的辐照响应行为

将类丁二炔(10, 12-二十五碳二炔酸)囊泡固载于琼脂糖凝胶制备出了新型辐射变色凝胶复合凝胶材料。利用γ射线辐照研究了所制备凝胶的辐照响应行为,结果显示:当γ辐射剂量在500-2000 Gy内,随着剂量增加,凝胶由无色逐渐变为蓝色,颜色不断加深,采用紫外-可见光分光光度计测试其吸收光谱,发现其主要吸收峰值在660 nm附近,且辐照前后凝胶的吸光度差值与剂量有良好线性关系(相关系数R² =0.9942)。进一步研究表明:所制备的凝胶材料对γ射线和电子束辐照有相同的剂量响应,且无明显的能量和剂量率依赖性;凝胶的辐射后效应较弱,辐照后24 h,吸光度基本恒定;分次辐照对凝胶剂量计准确性的影响极小;凝胶在0-30℃范围内的响应性基本保持稳定;在辐照后48 h内,并未观察到囊泡有明显扩散效应,显示出良好的稳定性。此外,琼脂糖具有价廉、无毒且易制备为任意形状凝胶的优点,因此该凝胶剂量计有望应用于真实场景的三维剂量分布测定。     

The response characteristics of tetrazolium violet solutions to gamma irradiation

The dosimetry characteristics of various solutions of tetrazolium violet, TV, (2,5-diphenyl-3-(1-naphthyl)-2H-tetrazolium chloride) to gamma irradiation are reported. The optical absorption spectra of these solutions show peaks between 400 and 600 nm with a shoulder at around 550 nm. The dose response of the optical absorbance values of aqueous and aqueous-alcoholic solutions containing different concentrations of TV was measured in the 250 Gy up to 75 kGy dose range. The formation of formazan product was observed due to radiolytic reduction in both solutions. Its formation was found more pronounced in N₂-saturated as well as in alkaline solutions. The results indicate that the 1 mM TV solution can be used for food irradiation and medical sterilization dosimetry at gamma irradiation facilities.     

Characterization of a new photo-fluorescent film dosimeter for high-radiation dose applications

Characterization studies on one of the first versions of the Sunna fluorescent dosimeter™ have been published by Kovács and McLaughlin. This present study describes testing results of a newer version of the dosimeter (Model γ, batch 0399-20). This dosimeter is a 1-cm×3-cm polymeric film of 0.5 mm thickness that emits a green fluorescence component at intensities almost linear with dose. The manufacturing method (injection molding) allows potential batch sizes on the order of a million while maintaining a signal precision on the order of ±1%. Studies include dose response, dose rate dependence, energy dependence, post-irradiation stability, environmental effects, and variation of response within a batch. Data for both food irradiation and sterilization dose levels were obtained. The results indicate that the green signal (0.3–250 kGy) works well for food irradiation dose levels, especially in refrigerated facilities that maintain tight temperature control. The green signal also works well in sterilization facilities because its irradiation temperature coefficient above room temperature is minimal at sterilization doses. If the user requires readout results in < 22 h after room temperature irradiation, the user can either calibrate for a specific post-irradiation readout time(s) or simply heat the dosimeters in a small laboratory oven to quickly stabilize the signal.     

Irradiation of ferrous ammonium sulfate for its use as high absorbed dose and low-temperature dosimeter

In the present paper, we study the response of crystalline ammonium ferrous sulfate as a function of the irradiation dose and temperature. The dose studied ranged from 33.5 to 546 kGy. The temperature regimen varied from 77 K (liquid nitrogen) to 311 K. The analysis of the samples was made by UV spectroscopy and EPR.The results show that the change in absorbance of the dosimeter was linear with respect to the absorbed dose in the range studied. There is a small influence of the irradiation temperature in the response of the iron salt. The dose rate and storage time after irradiation was of no importance in this application.     

Photoinactivation Sensitivity of Staphylococcus carnosus to Visible-light Irradiation as a Function of Wavelength

Inactivation properties of visible light are of increasing interest due to multiple possible fields of application concerning antibacterial treatment. For violet wavelengths, the generation of reactive oxygen species by porphyrins is accepted as underlying mechanism. However, there is still little knowledge about photosensitizers at blue wavelengths. While flavins were named as possible candidates, there is still no experimental evidence. This study investigates the photoinactivation sensitivity of Staphylococcus carnosus to selected wavelengths between 390 and 500 nm in 10- to 25-nm intervals. Absorption and fluorescence measurements in bacterial lysates confirmed inactivation findings. By means of a mathematical calculation in MATLAB^®, a fit of different photosensitizer absorption spectra to the measured action spectrum was determined to gain knowledge about the extent to which specific photosensitizers are involved. The most effective wavelength for S. carnosus at 415 nm could be explained by the involvement of zinc protoporphyrin IX. Between 450 and 470 nm, inactivation results indicated a broad plateau, statistically distinguishable from 440 and 480 nm. This observation points to flavins as responsible photosensitizers, which furthermore seem to be involved at violet wavelengths. A spectral scan of sensitivities might generally be an advantageous approach for examining irradiation impact.