Threonine-FX dosimeter for food irradiation

A detailed study for the spectrophotometric readout method for L-threonine powder, [CH₃CH(OH)CH(NH₂)COOH], was done. In this method, 400 mg unirradiated/irradiated L-threonine powder was dissolved in 10 ml of a solution which contains 3×10⁻⁴ mol dm⁻³ ferrous ammonium sulphate and 1.7×10⁻⁴ mol dm⁻³ xylenol orange (XO) in aerated aqueous 0.17 mol dm⁻³ sulphuric acid (FX). The peroxy radicals produced from irradiated threonine oxidize ferrous ions and XO forms a complex with ferric ions as well as controls the chain length of ferrous ion oxidation. The plot of absorbance at 556 nm against dose is linear in the dose range 20–400 Gy and doses down to about 1 Gy can be measured using 10-cm path cells. Response of the dosimeter is independent of irradiation temperature above 20. A dose of 50 Gy–10 kGy can be measured dissolving 50 mg threonine powder in 10 ml of a solution which contains 3×10⁻⁴ mol dm⁻³ ferrous ammonium sulphate and 1.3×10⁻⁴ mol dm⁻³ XO in aerated aqueous 0.06 mol dm⁻³ sulphuric acid (FX). The plot of absorbance at 552 nm against dose is non-linear. However dosimeter shows linear dose response up to 1000 Gy. Irradiated threonine powder is stable for about 3 months. The reproducibility of the method is better than ±2%. This dosimeter is very useful as transfer dosimeter for food irradiation programme.     

Gamma-ray dosimetry by spectrofluorimetry of phenylacetic acid solution

Aqueous solutions of phenylacetic acid have been evaluated for possible use in γ-ray dosimetry. When aerated aqueous phenylacetic acid solutions are irradiated, photoflourescent species are formed and identified as hydroxyphenylacetic acid. When excited by ultraviolet light at 280 nm, the radiation-induced product shows an emission spectrum with a maximum at 307 nm. The intensity of the emission peak at 307 nm (as well as the area under the peak from 290 to 350 nm) is a linear function of absorbed dose from 0.5 to 25 Gy. This aqueous dosimeter is about ten times more sensitive than that of the conventional ferrous sulfate solution (Fricke) dosimeter. The differences in response at dose rates in the range 0.0055–67 Gy/min are negligible. Conversely, at higher dose rates (170 Gy/min), although the response is linear with dose up to 135 Gy and with proper calibration can be used up to 350 Gy, the photofluorescence signal is somewhat greater than in the lower dose rate range. The estimated random uncertainty limits (1σ) of readings of absorbed dose by the dosimeter are approximately ±2% at a dose of 10 Gy. The fluorescence signal is very much affected by the hydrogen ion concentration of the solution and the intensity of the signal is greatest in the pH range 5–9.5. The radiation chemical yield of the fluorescing species is little influenced by moderate changes in the concentration of phenylacetic acid or by deaeration of the solution. The signal is stable up to at least four weeks, if the solution after irradiation is stored at low temperature (ca. 5°C). However, when stored at room temperature, and in room light, the signal is stable only up to about four days.     

Sensitivity and stability of the Fricke–gelatin–xylenol orange gel dosimeter

Spectrophotometric measurements of the Fricke–gelatin–xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25 Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy dosimetry measurements contains 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3.0% by weight gelatin.     

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.     

A novel approach towards development of real time chemical dosimetry using pulsating sensor-based instrumentation

The paper presents an innovative approach towards development of real time dosimetry using a chemical dosimeter for measurement of absorbed radiation dose in the range between 1 and 400 Gy. Saturated chloroform solution in water, a well known chemical dosimeter, is used to demonstrate the concept of online measurement of radiation dose. The measurement approach involves online monitoring of increase in conductivity of saturated chloroform solution due to progressive build up of traces of highly conducting HCl during exposure to gamma irradiation. A high performance pulsating sensor-based conductivity monitoring instrument has been used to monitor such real time change in conductivity of solution. A relation between conductivity shift and radiation dose has been established using radiochemical yield value (G value) of HCl. The G value of HCl in saturated chloroform dosimeter has been determined using laboratory developed pulsating sensor-based devices. In this connection dose rate of Co-60 gamma chamber was determined using Fricke dosimeter following a simple potentiometric measurement approach developed in-house besides conventional spectrophotometry. Results obtained from both measurement approaches agreed well. Complete instrumentation package has also been developed to measure real time radiation dose. The proposed real time radiation dosimeter is successfully tested in several measurement campaigns in order to assure its performance prior to its deployment in field.     

Gamma-ray response of a clear,crosslinked PMMA dosimeter,Radix W

Radix W, a clear poly(methyl-methacrylate) (PMMA) dosimeter was developed with improved properties compared to the conventional clear PMMA dosimeter, Radix RN15. PMMA with a glass transition temperature (T_g) higher than 120 °C was selected making it possible to measure doses in a wide range of 1 to 150 kGy. Dose rates of 2.5–10 kGy/h were tested and did not affect significantly the dose response. The influence of irradiation temperature was reduced compared with Radix RN15.     

Evaluation of an indigenously manufactured Garfilm-EM—250 μm thick polyester film as a dosimeter for high-dose applications

Dosimetric characteristics of indigenously manufactured ‘Garfilm-EM’—a 250 μm thick polyester film—were evaluated spectrophotometrically for its possible application as a routine film dosimeter in gamma radiation processing. Available commercially in large batches, this film is cheap, has a good clarity, consistent thickness, is scratch resistant and is easy to handle. Radiation-induced changes in the absorption spectra of Garfilm were analysed and based on the results obtained, 340 nm was chosen as the wavelength of absorption measurements. The reproducibility of the response of these films for cobalt-60 gamma rays was found to be within ±2.7% (1σ). In the present study, influence of environmental conditions during irradiation like irradiation temperature, relative humidity, oxygen content and dose rate on dose response of Garfilm were also investigated systematically. From the studies carried out, Garfilm-EM has been found to have a good potential for its use as a dosimeter in the absorbed dose range 20–220 kGy due to its linear dose–response relationship, good pre- and post-irradiation stability and reproducibility.     

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.     

Optimizing the sensitivity and radiological properties of the PRESAGE® dosimeter using metal compounds

The aim of this study is to investigate the radiation-modifying effects of incorporating commercially available bismuth-, tin- and zinc-based compounds in the composition of the PRESAGE^® dosimeter, and the feasibility of employing such compounds for radiation dose enhancement. Furthermore, we demonstrate that metal compounds can be included in the formulation to yield water-equivalent PRESAGE^® dosimeters with enhanced dose response. Various concentrations of the metal compounds were added to a newly developed PRESAGE^® formulation and the resulting dosimeters were irradiated with 100 kV and 6 MV photon beams. A comparison between sensitivity and radiological properties of the PRESAGE^® dosimeters with and without the addition of metal compounds was carried out. Optical density changes of the dosimeters before and after irradiation were measured using a spectrophotometer. In general, when metal compounds were incorporated in the composition of the PRESAGE^® dosimeter, the sensitivity of the dosimeters to radiation dose increased depending on the type and concentration of the metal compound, with the bismuth compound showing the highest dose enhancement factor. In addition, these metal compounds were also shown to improve the retention of the post-response absorption value of the PRESAGE^® dosimeter over a period of 2 weeks. Thus, incorporating 1–3 mM (ca. 0.2 wt%) of any of the three investigated metal compounds in the composition of the PRESAGE^® dosimeter is found to be an efficient way to enhance the sensitivity of the dosimeter to radiation dose and stabilize its post-response for longer times. Furthermore, the addition of small amounts of the metal compounds also accelerates the polymerization of the PRESAGE^® dosimeter precursors, significantly reducing the fabrication time. Finally, a novel water-equivalent PRESAGE^® dosimeter formula optimized with metal compounds is proposed for clinical use in both kilovoltage and megavoltage radiotherapy dosimetry.     

Some Physico-Technical Aspects of the New Generation of Self-Calibrated Alanine/EPR Dosimeter and Results from the International Intercomparison trial

Some physico-technical parameters of the self-calibrated alanine/EPR dosimeters are described. Principally, this new type of solid state/EPR dosimeter contains radiation sensitive diamagnetic material (in the present case, alanine), some quantity of EPR active, but radiation insensitive, substance (for example, Mn²⁺/MgO) playing roles of an internal standard and a binding material. Thus with this dosimeter the EPR spectra of alanine and the internal standard Mn²⁺ are recorded simultaneously and the dose response is represented as a ratio of EPR signal intensities of alanine versus Mn²⁺ as a function of absorbed dose. As a result, the data of the present study have shown that there is practically no interference of the dosimeter EPR response (expressed as the ratio I _alanine/I _Mn) from the way of preparation (homogeneity), behavior after irradiation (fading of EPR signals with time, influence of different meteorological conditions) as well as specific spectrometer setting conditions. These dosimeters show satisfactory reproducibility of preparation and reading as well as stability on keeping. Thus, fulfilling the described physico-technical data of this type of dosimeters, the reproducibility of the readings is significantly improved particularly when intercomparison among different laboratories is performed. This conclusion is confirmed by independent studies of the described self-calibrated alanine/EPR dosimeters in several laboratories in Europe. Results of which are also reported.     

Effect of inorganic salt on the dose sensitivity of polymer gel dosimeter

The effect of inorganic salts, non-transition metal chlorides, on the dose sensitivity of methacrylic-acid-based polymer gel dosimeter is investigated. Dose-R₂ responses are obtained from magnetic resonance imaging data. Temperature increase due to exothermic polymerization reaction in the gel is also measured directly during irradiation. As a result, substantial increases in R₂ response are observed in the polymer gel dosimeter containing inorganic salt, especially with MgCl₂. The sensitivity of the gel with 1.0 M MgCl₂ is approximately 2.8 times higher than that of without MgCl₂. As the salt concentration increases, an increase of polymerization rate is also observed via the temperature measurements. These results indicate that inorganic salt acts as an accelerator for radiation-induced free-radical polymerization in methacrylic-acid-based gel.     

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。     

A new dosimetry system using a portable reader

A new dosimeter material has been developed which consists of a radiation sensitive layer on a reflective base, and utilises a portable microdensitometer for response measurement. The instrument, modified from a readily available hand-held unit, is a standard in the printing industry. The system was designed with the demands of ‘in plant’ use in mind, and is equally suitable for either gamma or electron beam irradiation. The dosimeter material develops an easily visible colour change, which is quantitative, highly reproducible and stable over the dose range of approximately 5–45 kGy. The results presented demonstrate the calibration and characteristics of the dosimetry system, and explore some of its potential.     

A new label dosimetry system

A new label dosimeter which changes its color by large radiation doses has been developed. The green color of the unirradiated dosimeter gradually turns to brown then to red at high doses. The label dosimeter was prepared with a peal-off paper backing, allowing it to stick by self-adhesion to a product box. Three types of dosimeters having different sensitivities to radiation doses were prepared. Correlations were established between absorbed doses and color scale or the green/red axis of the irradiated dosimeters, using a micro color unit equipped with a data station. The data were analyzed to determine the reproducibility of the reflectance measured from the label dosimeters exposed to different doses of γ radiation. These dosimeters showed great stability on extended storage before and after irradiation.Detailed measurements of absorbed dose extremes (D_min and D_max) in product boxes, processed in the Egypt Mega Gamma I radiation processing facility, were obtained using these dosimeters. These dosimeters are currently available in large quantities and are inexpensive, which makes them suitable for routine high-dose applications in radiation processing of materials.     

Temperature response of a number of plastic dosimeters for radiation processing

Various plastic dosemeters are employed for dosimetry control of radiation processing within gamma and electron irradiation facilities.

The temperature response of a dosimeter is important when the dose to such a dosimeter is accumulated under varying irradiation temperatures. Such measurements would be significant for proper assessment of the dose for better process control, as well as, performance evaluation of dosimetry systems.

In this work we have developed a high current peltier junction temperature controller system for our Gammacell-220. This system has been designed to regulate the operating temperature of the irradiation chamber in the range of 0 to 80 C this system has been applied to measure the temperature response of the red perspex, a local clear PMMA, Gammex, Gammachrome, and Gafchromic dosimeters. The curves of relative performance or variation of the induced optical densities of the above dosemeters versus the irradiation temperature at fixed dose values are obtained.     

Ammonium dithionate- a new material for highly sensitive EPR dosimetry

Polycrystalline ammonium dithionate has been examined for its radiation response in the low dose range (<5Gy) using EPR technique. The SO(3)(-) radical ion was detected as a single EPR line with a peak-to-peak derivative width of ca. 0.44mT in irradiated samples and its intensity was found to vary linearly with dose. At equal and moderate settings of microwave power and modulation amplitude ammonium dithionate was at least seven times more sensitive than l-alanine which is the most common EPR dosimeter standard. Pulse experiments were performed on the powder samples to obtain the longitudinal relaxation time. These and microwave saturation experiments served to indicate the optimal microwave power to be applied during measurements as an EPR dosimeter for best sensitivity of this material. It is thus claimed that ammonium dithionate has excellent potential to become an EPR dosimeter with a low limit of the measurable dose for cases where tissue equivalence is not required or can be corrected for.     

Thermoluminescence characteristics of neodymium-doped silicon dioxide optical fibers subjected to X-ray

In this article, we investigate thermoluminescence properties of Nd³⁺ doped silicon dioxide optical fiber. The samples were exposed to 10 MV X-ray using a linear accelerator. The optical fiber was read out using Harshaw 3500 TLD reader. Nd-doped optical fiber displays a linear TL response for the absorbed dose. The sensitivity of Nd-doped optical fiber is 82.87 nC. mg^–1 Gy^–1, which is more sensitive to the other types of optical fiber. Nd⁺³-doped optical fiber displays clear single glow peak around 180°C. The peak shape method analysis reveals that the peaks obey general order kinetics. The activation energy of Nd-doped optical fiber is found to be nearly 0.5 eV less than TLD-100 (1.6 eV). Z_eff of neodymium-doped silicon dioxide optical fiber is 13.48 that is near to the human bone. All of these TL characteristics indicate that Nd107-doped optical fiber as a potential TL dosimeter, for measuring photon irradiation.     

Effect of γ-irradiation on the physicochemical and sensory properties of hazelnuts (Corylus avellana L.)

The present study evaluated the quality of hazelnuts as a function of irradiation dose to determine dose levels causing minimal undesirable changes to hazelnuts. Physicochemical (color, peroxide value (PV), hexanal content, fatty acid composition and volatile compounds) and sensory (color, texture, odor and taste) properties were determined.Results showed a twenty fold increase in peroxide value and twenty-eight fold increase in hexanal content after irradiation at a dose of 7 kGy. An increase was also observed in saturated fatty acids (10%–23%) with a parallel decrease in unsaturated fatty acids (90–77%). Volatile compounds such as ketones, alkanes, alcohols, aldehydes, furans, aromatic hydrocarbons, bicyclic monoterpenes and acids were produced mostly comprising secondary oxidation products of hazelnut lipids after irradiation. Color parameter b* increased (p<0.05) after irradiation at a dose of ⩾5 kGy, while color parameters L* and a* remained unchanged by irradiation. Sensory evaluation showed that texture and color were not affected by irradiation. Taste, the most sensitive sensory attribute showed that hazelnuts retain acceptable sensory quality when irradiated up to a dose of 1.5 kGy.     

Preliminary investigation of a new type of propylene based gel dosimeter (DEMBIG)

Radiotherapy widely uses the polymer gel dosimeter. The advantage of polymer gel dosimetry is the mapped 3D absorbed dose distribution that other dosimeters cannot achieve. The Acrylamide (AAm) is a frequently used monomer; however, the extreme toxicity of Acrylamide (ORL-RAT LD50: 124 mg/kg) raises a concern. Therefore, this study developed a new type of Propylene acid based gel dosimeter, named DEMBIG gel. The following outlines the aim of this study: (1) using two-point formulation to find the optimal scan parameter of MRI according to the best sensitivity and linearity (correlation coefficient) of DEMBIG gel, (2) using the optimal scan parameter of MRI to observe the properties of DEMBIG gel, and (3) verifying the three-dimensional (3D) dose distributions of radiotherapy. This study obtained three major results: 1. The scan protocol of MRI was established. 2. The preliminary results of DEMBIG gel were: (1) The range of absorbed dose of DEMBIG gel: 0–20 Gy. (2) The sensitivity and correlation coefficient of DEMBIG gel at verification as slope: 0.181 sGy^?1, R ²:0.997. (3) There is no energy dependency of the DEMBIG gel. 3. The dose difference was 3% in the three-dimensional (3D) isocenter dose in clinical radiotherapy. These data show that DEMBIG gel is a potential candidate for the 3D dosimeter.     

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