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.     

The operational benefits of integrated PC control of gamma irradiation plants

Compared with the traditional PLC control systems used on many gamma irradiation plants, the semi-intelligent decision making capabilities of a fully integrated PC control system can bring many benefits to the plant operator.

The authors will describe how plant operation is fully automatic with the PC control providing all the input-output data required to run the plant efficiently and safely. Detailed product tracking, with live on-screen data, can be incorporated to give both plant operator and product manufacturer complete confidence in the irradiation process. Advanced features such as on-line diagnostics and mechanical part failure prediction are also described.

Also available is automated dosimetry, reducing the opportunity for human error, whilst at the same time saving on staff costs and providing highly professional dose validation reports and comprehensive routine dosimetry documentation.

The benefits of PURIDEC's PC control system are not only available with its new plants. The system can be supplied as an upgrade to plants of all ages and design giving the current operator all the benefits described in the paper.     

Development of polystyrene calorimeter for application at electron energies down to 1.5 MeV

Polystyrene (PS) calorimeters developed at Riso National Laboratory for use below 4 MeV have been modified due to irradiation technology requirements concerning both design principles and dimensions. The temperature–time relationship after irradiation was measured, and two ways of dose measurement were tested: (1) real time temperature measurement during the irradiation and (2) pre- and post-irradiation temperature measurement. The advantages and drawbacks of these methods are discussed.Depth dose measurements have been carried out in the PS calorimeter to define the relationship between the average and the surface dose and to prove the applicability of the new low energy calorimeter for calibration purposes at 1.5 and 2 MeV electron energy. Alanine dosimeters of 2 mm thickness were used to calibrate the calorimeters and their use for nominal dose measurements was demonstrated in a series of intercomparisons. The use as routine dosimeters at electron accelerators operating in the energy range of 1.5–4 MeV was also demonstrated.     

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.     

Theoretical evaluation of dose distribution in product in radiation processing plants

An analytical method has been developed for the computation of dose rates at any number of points in the product material in a radiation processing plant in which radioactive source pencils are arranged in a rectangular vertical frame. Exposures from each individual source pencil and the movement of the product box was taken into consideration for the evaluation of absorbed dose. The validity of the computational method was tested for one of the existing irradiator already in operation. Excellent agreement was achieved between the computation and measured values of doses received by the product material. The method was then applied in the design of a new irradiator and was found very useful to arrive at optimum source size and target size. Hence, this method is being adopted for the design of all forthcoming ⁶⁰Co irradiation plants in India.     

Dyed polyvinyl chloride films for use as high-dose routine dosimeters in radiation processing

Characteristics of the polyvinyl chloride (PVC) films containing 0.11 wt% of malachite green oxalate or 6GX-setoglausine and about 100 μm in thickness were studied for use as routine dosimeters in radiation processing. These films show basically color bleaching under irradiation with ⁶⁰Co γ-rays in a dose range of 5–50 kGy. The sensitivity of the dosimeters and the linearity of dose-response curves are improved by adding 2.5% of chloral hydrate [CCl₃CH(OH)₂] and 0.15% hydroquinone [HOC₆H₄OH]. These additions extend the minimum dose limit to 1 kGy covering dosimetry requirements of the quality assurance in radiation processing of food and healthcare products. The dose responses of both dyed PVC films at irradiation temperatures from 20°C to 35°C are constant relative to those at 25°C, and the temperature coefficients for irradiation temperatures from 35°C to 55°C were estimated to be (0.43±0.01)%/°C. The dosimeter characteristics are stable within 1% at 25°C before and 60 days after the end of irradiation.     

Electron-beam processing for sterilization

High-powered, 10-MeV linear accelerators offer advantages for sterilization of medical products. A highly effective quality assurance program must be in place to ensure the appropriate dose is delivered to each product unit and that all required documentation is produced. The key elements of such a program are establishing the routine processing window for each product, maintaining process control and demonstrating compliance.     

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.     

The possibility of using radiation-reclaimed butyl rubber in the building industry

Studies are performed to demonstrate the possibility of the valuable replacement of butyl rubber by a radiation-induced degradation product for the production of different waterproofing and roofing materials in the building industry. The efficiency of using nitroso compounds, such as p-dinitrobenzene and quinol ether, as vulcanizing agents is investigated. It is shown that a reclaimed product obtained at an irradiation dose of 20 Mrad may be used as an efficient adhesive additive. The addition of such a reclaimed product to a solution-born mastic in an amount of 30 mass parts per 100 mass parts of rubber substantially enhances the adhesion to concrete, steel, polyethylene, etc. other properties remaining unchanged.     

正辛醇的γ辐照稳定性及辐解产物分析

在高放射性废液后处理的萃取工艺中, 正辛醇被认为是具有应用前景的稀释剂之一, 而研究其γ辐射效应对指导其实际应用具有重要意义. 本文对N2环境下γ辐照后的正辛醇进行了紫外-可见(UV-Vis)光谱和傅里叶变换红外(FTIR)光谱研究. 结果表明正辛醇在100 kGy以下辐照后化学结构未发生变化, 而吸收剂量增至300 kGy时有羰基化合物生成. 通过色谱(GC)和色质联用(GC-MS)进一步分析了高剂量(600 kGy)辐照后正辛醇的气体及液体辐解产物, 发现主要气体产物为H2, 并伴有微量的CO2和CH4; 主要液体产物为正辛醛, 其占未辐解正辛醇的质量百分含量小于1%, 并伴有少量正庚烷和8-羟基十五醇. 对辐照后正辛醇的化学结构及辐解产物的分析表明, 正辛醇在氮气下经γ辐照后, 主要发生α碳原子上的C—H键断裂,并伴有β碳原子上的C—C键断裂. 此外, 抽氢反应也是正辛醇辐解的重要途径.     

Dosimetric properties of commercial grade plexiglas as a possible routine dosimeter for radiation processing

Dyed and undyed polymethylmethacrylate (PMMA) are commercially available for high dose dosimetry in radiation processing applications. In order to investigate the properties of the locally available clear perspex as a subsitute routine dosimeter, we have looked into the optical and dosimetric properties of clear perspex sheets with a thickness of 2 mm.

The selected wavelength used for read out was 314 nm. Absorption spectra obtained showed a sharp cutoff at 260 nm wavelength. Post-irradiation studies at different doses indicate that the optical density decrease with storage time. No significant dose rate dependence in the range of 1.1 to 11 kGy/hr has been observed. The temperature response of the said clear perspex in the range of 0–30°C during irradiation has also been determined.

Comparison of the optical density versus dose for the local clear perspex against that of red perspex from Harwell, at an absorbed dose of 25 kGy, as obtained in our gamma irradiator, IR-136, showed a difference of 3%. The reproducibility of the local clear PMMA has been observed to be also less than 3% in an absorbed dose range of 5 to 50 kGy.     

Irradiation plant control upgrades and parametric release

This paper reviews an integrated PC irradiation plant control system which is one of the most advanced available. The system controls the entire irradiation process from ‘goods in’ through to dosimetry and the production of post-irradiation documentation. Product processing speeds are automatically calculated by reference to validation data which ensures that the dose requirements are met. Detailed product tracking and data logging of all plant activities ensures traceability of the entire irradiation process. The paper demonstrates how the system effectively enables parametric release of products since the critical processing parameters are automatically set, monitored and recorded and are directly linked to the validation of these parameters.     

Dosimetry characteristics of the nitro blue tetrazolium-polyvinylalcohol film for high dose applications

The dosimetry characteristics of a polyvinylalcohol based radiochromic dye film containing the ditetrazolium salt nitro blue tetrazolium chloride were studied with respect to the potential use of the films for routine dosimetry in radiation processing. The useful dose range for the dosimeter film for gamma and electron irradiation is 5–50 kGy depending on the concentration of the dye. The effects of irradiation temperature and humidity, as well as the stability of the response of the film before and after irradiation, were investigated and determined. Formulations for preparation of the films with different concentrations of the dye and with different pH were tested. The films were also tested in industrial gamma irradiation facilities for process control purposes by comparing their performance with transfer standard dosimeters.     

Improvement of plant parameters of the ROBO gamma irradiation facility due to design modification

Two industrial scale, “ROBO” type ⁶⁰Co gamma irradiation facilities have recently been put into operation in Syria and Peru, and the dosimetry commissioning of both plants have been carried out to determine dose distribution within products and to calculate plant parameters such as efficiency, dose uniformity ratio and throughput. There are some design modifications between the two plants in connection with the location of the carriers with respect to the source plaque and also to each other. The effect of these construction modifications on the plant parameters is discussed in the analysis of the dose distribution data measured in the carriers with depth and height among the four irradiation rows on both sides of the source plaque. The plant parameters were also calculated for different product densities using the technical data of the facilities, and the calculated and measured results were compared to each other.     

The efficacy and progress in using radiation as a quarantine treatment of tropical fruits—a case study in Hawaii

Most tropical fruits for export must be treated with an approved quarantine treatment. Three and a half decades of research have demonstrated the efficacy of irradiation as a quarantine treatment in terms of efficiency, effectiveness, and product quality retention. The USFDA and the USDA-APHIS approved irradiation to disinfest fresh foods/fresh papayas in 1986 and 1989, respectively. In early 1995, the Hawaii Department of Agriculture was granted a special permit from USDA-APHIS allowing untreated Hawaiian fruits to be irradiated on the US mainland. The objectives were to gain experience in commercial irradiation as a quarantine treatment and to gather data on shipping and handling procedures, and on product quality. In April 1995, the first shipment of Hawaiian fruit was irradiated at a minimum quarantine dose of 0.25 kGy in an Isomedix plant near Chicago, and then distributed to supermarkets in Illinois and Ohio. Continuous shipments, irradiation, and marketing of various tropical fruits in the US have shown commercial efficacy, quality retention, and excellent consumer acceptance. A commercial e-beam/converted X-ray facility was installed by Titan Corp. on the Island of Hawaii and was operational by late July 2000. Hawaii has become the first place in the world to use irradiation as a quarantine treatment of fruits.     

Polymerization as a limiting factor for light product yields in radiation cracking of heavy oil and bitumen

The kinetic model of radiation-thermal and low-temperature radiation cracking is developed subject to the specificity of radiation-induced processes and the effect of structure in extremely heavy hydrocarbon feedstock. Theoretical calculations are compared with the available experimental data. The dependences of the cracking product yields on temperature, dose and dose rate of ionizing irradiation are analyzed on the base of the developed model subject to the structural state of the feedstock. Radiation-induced polymerization and chemical adsorption are considered as the important factors limiting heavy oil conversion.     

Leakage radiations in a medical electron accelerator facility--measurement of neutrons and comparison with calculation

Neutron dose equivalent rates are measured in the irradiation room and the maze of a medical electron accelerator facility. An m-counter used for measurement is associated with a gate circuit to reject piled up signals caused by pulsed X-rays, so that it is possible to measure the neutrons without obstruction by the piled up signals even in the irradiation room. Counting loss of neutrons is mathematically corrected, and the correction factor comes nearly equal to 1.5 at dose points close to the entrance to the irradiation room when 14 MV X-rays are generated. The measurement in the maze agrees with the calculation reported in the preceding report in a factor less than 1.5 except for dose points close to the entrance to the irradiation room.     

Modification on liquid retention property of cassava starch by radiation grafting with acrylonitrile. I. Effect of γ-irradiation on grafting parameters

Radiation modification on liquid retention properties of native cassava starch, gelatinized at 85°C, by graft copolymerization with acrylonitrile was carried out by mutual irradiation to gamma-rays. A thin aluminum foil was used to cover the inner wall of the reaction vessel, so that the homopolymer concentration was reduced to be less than 1.0% with a distilled water retention value of 665 g/g of the dry weight of the saponified grafted product. Confirmation of graft copolymerization and saponification reactions was made by the infrared spectrophotometric technique. The combined effect of radiation parameters in terms of an irradiation time and a dose rate to the total dose on the extent of the grafting reaction expressed in terms of grafting parameters which directly influenced liquid retention values was evaluated in conjunction with statistical analysis.     

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.     

Sunna dosimeter: an integrating photoluminescent film and reader system; work in progress

A new radiation dosimeter, consisting of an optically-stimulated polymer film containing a photofluorescent sensor, can serve as a routine dosimeter and radiographic imaging medium for high-dose applications in the absorbed dose range 0.1–100 kGy. The flexible, colorless, opalescent film having a uniform thickness of 0.240 (±0.005) mm or certain other films in the thickness range 0.08–0.60 mm, are available in large batches. They can be read rapidly with a simple table-top spectrofluorimeter, excitation wavelength (λ=450 nm) and emission wavelength (λ=670 nm), giving a type A uncertainty of dose evaluation of <±5% at 95% confidence level. It supplies either single integrated dose readings or two-dimensional radiographic images with relatively high spatial resolution. The present work focuses on the following gamma-ray response characteristics of the system: inter- and intra-batch reproducibility, pre- and post-irradiation stability, and dependence of dose interpretations on absorbed dose rate and irradiation temperature.