Effects of elevated temperatures during interruption of irradiation on Harwell Red 4034 PMMA and Kodak Biomax alanine film dosimetry systems

In the industrial setting it is not uncommon for a process interruption to occur during irradiation. In this event, dosimeters may be exposed to prolonged periods of elevated temperature without exposure to ionizing radiation. Once the process is restarted, the same dosimeters are exposed to ionizing radiation in order to achieve target dose. The goal of this experiment was to simulate a process interruption within limits and quantify the effects of a combination of factors (heat, time, and fractionation) on dosimeter response. We present an in-depth experimental study on the response of dosimeters that have been irradiated, stored for a fixed period of time at several temperatures, and then re-irradiated. This study was performed using Harwell Red 4034 polymethylmethacrylate (PMMA) and Kodak BioMax alanine film dosimeters.     

AlanineESR Dosimetry system for routine use in radiation processing

A new alanine-polystyrene (PS) dosimeter prepared with simplified molding procedure and an automatic desk-top dose-reader of alanine dosimeter were developed for the purpose of routine use. Combination of these two allows us to apply a reliable alanine/ESR dosimetry system to routine dosimetric process control in industrial gamma radiation processing.     

Recent progress in JAERI alanineESR dosimetry system

Alanine/ESR (electron spin resonance) dosimetry system has been developed on the basis of precise, mass-productive alanine dosimeters of various shapes, and easy-handling ESR reading system. Polymers as binders enable us to mass-produce homogeneous and dimensionally uniform alanine dosimeters of different shapes and thickness relative to penetration range of radiations, for instance, rods for gamma and X-rays, and thin films for electrons and heavy charged particles. They also allow us to simplify parameters of ESR operation exclusively for specific dosimeters and to achieve good reproducibility of measurement. An easy-handling ESR spectrometric reading system was developed on the basis of custom-made ESR spectrometer with a permanent magnet, and automated with auxiliary interfaces and a personal computer. Alanine/ESR dosimetry in JAERI works for domestic and international transfer dosimetry, for simple and reliable routine dosimetry in radiation processing, and for dosimetry of short-penetration range radiations.     

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.     

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.     

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.     

Applicability study on existing dosimetry systems to high-power Bremsstrahlung irradiation

Applicability of the existing dosimetry systems to high-power Bremsstrahlung irradiation was investigated through a dose intercomparison study, where several dosimeters were irradiated in the dose range 4–12 kGy in identical polyethylene phantoms in a Bremsstrahlung beam obtained from a 5-MeV electron accelerator. Included in the study were alanine dosimeters molded by three different binders, three types of liquid dosimeters—ceric-cerous, dichromate and ethanol-chlorobenzen (ECB), and glutamine powder. The dosimeter responses for Bremsstrahlung radiation were analyzed at the issuing laboratories, and the dose values determined using calibration based on cobalt-60 gamma-ray irradiation. Dose values for all the three dose levels for all dosimetry systems were in good agreement—better than 3%. The results of the study demonstrate that these existing dosimetry systems have a potential for application to high-power Bremsstrahlung irradiation.     

Uncertainties in absorbed dose as measured using PMMA dosimeters

Some Harwell quality-control data on red 4034 PMMA dosimeters are presented, showing that gaussian distribution and probability apply to the specific absorption measurements used to derive dose.

Uncertainties of calibration and use are listed, quantified, and combined in simple quadrature, for an example batch of dosimeters. The overall uncertainty of calibration derived from this listing is shown to agree with the average uncertainty found in a closed-loop inter-laboratory comparison exercise.     

Use of maximum temperature for correction of alanine dosimetry in electron beams

Alanine dosimetry is well characterized for irradiation temperature response. In use, alanine absorbed dose response is corrected for the irradiation temperature. The temperature used to correct alanine dosimetry absorbed dose response in electron beams has historically been the mean temperature occurring during irradiation (Sharpe and Miller, 2009). At lower absorbed doses, the change in temperature is relatively low; thus the absorbed dose response correction due to temperature is small. However, industrial electron beam processing often requires higher absorbed dose measurements where the change in temperature can be very large and the corresponding dose response correction for alanine becomes significant. This paper compares the impact of the temperature correction based on the use of a mean irradiation temperature (Sharpe and Miller, 2009) versus the use of a maximum irradiation temperature on the absorbed dose measurement. The results of this comparison indicate that the use of a mean temperature correction for higher absorbed doses measured with temperature corrected alanine dosimetry introduces a bias in the absorbed dose estimate.     

Uncertainty estimation in Co gamma-ray dosimetry at JAERI involving a two-way dose intercomparison study with NPL in the dose range 1–50 kGy

The uncertainties in ⁶⁰Co gamma-ray dosimetry at JAERI have been estimated by reviewing irradiation and calibration procedures. The uncertainty in dose delivered by the JAERI calibration system has been estimated to be 2.2% (2σ) and the uncertainty in dose measurement using JAERI alanine/ESR transfer dosimeters has been estimated to be 3.4% (2σ). A two-way dose intercomparison study between NPL and JAERI employing alanine-PS, alanine-paraffin, and dichromate dosimeters as transfer dosimeters was performed to confirm the estimated uncertainty over the dose range 1–50 kGy. Dose intercomparison results using both alanine and dichromate dosimeters show agreement within about 2%, which gives confidence in the estimated uncertainty in ⁶⁰Co gamma-ray dosimetry at JAERI.     

A study of some parameters relevant to the response of harwell PMMA dosimeters to gamma and electron irradiation

The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.

This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life.     

Standardization and regulatory control on radiation processing dosimetry in China

In 1983, in order to suit the rapid development of radiation processing, a programme of high dose standardization was initiated in China. As a result, a high dose measurement system for gamma - rays including primary standards, transfer standards and working dosimeters, has been established. In this paper, the scheme of dosimetry traceability to national standards for gamma - rays is illustrated. The aspects of standardization and the progress of dosimetry of radiation processing are also outlined.

In order to implement “the Law on Metrology of the Peoples Republic of China” and to guarantee the product quality of radiation processing. SBTS and SCTS have jointly issued “the Provisional Regulation of Metrological Supervision and Management for Radiation Processing”. A series of national standards, verification regulations and technical norms have been enacted and issued on the radiation processing dosimetry and on the approval of irradiation facilities. These documents are expected to play significant roles in the dose measurement standardization and the regularity control.     

Solid state "self-calibrated" EPR-dosimeters-advantageous and shortcomings

EPR dosimetry method with alpha-alanine as radiation sensitive material (RSM) is widely used in high dose dosimetry laboratories. However, it is not suitable for routine industrial applications mainly because of difficult EPR measurement procedure. In order to simplify quantitative EPR dosimetry measurements Yordanov and Gancheva developed so-called "self-calibrated" (sc) dosimeters consists of RSM (alpha-alanine, sugar, other ones), Mn2+/MgO as internal EPR intensity standard (IES) and a binder. The aim of this work was to check dosimetric properties of two experimental batches of sc EPR dosimeters with alpha-alanine and sugar as RSM, Mn2+/MgO as IES and paraffin as a binder. The percentage content of the components was 60, 5 and 35% (w/w), respectively. It was established that the investigated alanine sc-dosimeters are about two times more sensitive than the sugar ones. The dose-response coefficient, K(dr) of sc-alanine dosimeters was stable in all investigated dose range from 1 to 23 kGy. The K(dr)-value of sugar sc-dosimeters decreased with the dose what was in a contradiction to the results pointed to the high stability of radiation generated sugar radicals. The observed effect arose probably from the special chemical procedure used for the sc-sugar dosimeters production. The results confirmed an expectation that the position of sc dosimeter in the cavity is not important factor for accurate dose evaluation. It allows to read-out dosimetric signals in shorter time, with lower uncertainty and on less sophisticate EPR-spectrometers than that commonly used till now. The main shortcomings of sc dosimeters are: (a) the limitation of RSM suitable for sc dosimeters to these ones having strictly linear signal to dose characteristic; (b) necessity to assure very good homogeneity of dosimeter material; and (c) the cost of IES present in the amount of some percent in each sc dosimeter.     

Measurement of dose given by Co-60 in radiotherapy with TLD-500

The uses of dosimeters based on optically stimulated luminescence technique have become widespread in clinical applications. In the present study, the dose values given by Cobalt-60 radiotherapy machine were measured with optically stimulated luminescence (OSL) technique using TLD-500 and compared with those of commonly used ionization chamber dosimeter system. The percentage depth dose (DD%) values and graphs were formed. OSL system with TLD-500 can be reliably used as medical and personal dosimeter.     

Effects of humidity and light on dosimetric properties of clear polymethylmethacrylate

Effects of humidity and light conditions /fluoroscent light, sunlight and diffuse sunlight/ on the response of 2 mm thick clear polymethylmethacrylate /PMMA/ dosimeter during irradiation and during postirradiation storage were determined spectrophotometrically at 305 and 314 nm. The results showed that irradiation of dosimeters at 12–97% relative humidity did not result in any change in the response upto 2 weeks of post-irradiation storage. However, there is some decrease in the response at higher humidities />76%/ for longer storage time. Post-irradiation storage and dosimeters at constant relative humidity conditions between 35 and 97% had no effect on the response up-to 3 weeks. Post-irradiation storage at lower relative humidity /12%/ showed some decrease in the response for longer periods. The response of dosimeter is not very sensitive to short time exposure to diffuse sunlight and fluorescent light. However, a significant increase in the optical density was observed during exposure of dosimeters to direct sunlight.     

Application of egs4 computer code for determination of gamma ray spectrum and dose rate distribution in gammacell 220

The EGS4 a Monte Carlo electron-photon transport simulation package together with a locally developed computer program “GCELL” has been used to simulate the transport of the gamma rays in Gammacell 220. An additional lead attenuator has been inserted in the chamber, has been included for those cases where lower dose rates were required.

For three cases of 0, 1.35 and 4.0 cm thickness of added lead attenuators, the gamma spectrum, and dose rate distribution inside the chamber have been determined. For the case of no attenuator present, the main shield around the source cage has been included in the simulation program and its albedo effects have been investigated.

The calculated dose rate distribution in the Gammacell chamber has been compared against measurements carried out with Fricke, PMMA and Gafchromic film dosimeters.     

Advancements in internationally accepted standards for radiation processing

Three subcommittees of the American Society for Testing and Materials (ASTM) are developing standards on various aspects of radiation processing. Subcommittee E10.01 “Dosimetry for Radiation Processing” has published 9 standards on how to select and calibrate dosimeters, where to put them, how many to use, and how to use individual types of dosimeter systems. The group is also developing standards on how to use gamma, electron beam, and x-ray facilities for radiation processing, and a standard on how to treat dose uncertainties. Efforts are underway to promote inclusion of these standards into procedures now being developed by government agencies and by international groups such as the United Nations' International Consultative Group on Food Irradiation (ICGFI) in order to harmonize regulations and help avoid trade barriers.

Subcommittee F10.10 “Food Processing and Packaging” has completed standards on good irradiation practices for meat and poultry and for fresh fruits, and is developing similar standards for the irradiation of seafood and spices. These food-related standards are based on practices previously published by ICGFI.

Subcommittee E10.07 on “Radiation Dosimetry for Radiation Effects on Materials and Devices” principally develops standards for determining doses for radiation hardness testing of electronics. Some, including their standards on the Fricke and TLD dosimetry systems are equally useful in other radiation processing applications.     

Preparation of W1/O/W2 emulsion to limit the diffusion of Fe3+ in the Fricke gel 3D dosimeter

The irradiation of tumors in radiotherapy requires accurate 3D dosimetry. The Fricke 3D dosimeters, which were considered to be high potential of application in 3D dosimetry, suffer from a reduced temporal integrity of dose distribution caused by Fe³⁺ ions diffusion. To overcome the drawback, we firstly synthesized a kind of amphiphilic molecules with critical micelle concentration of 0.45 g/L and hydrophile‐lipophile balance value of 10, then prepared multiple emulsions by self‐assembling those molecules in Fricke solution under liquid paraffin, and finally obtained Fricke hydrogel embedded with the multiple emulsions. The diffusion coefficient of Fe³⁺ ions in the embedded Fricke hydrogel was measured to be 0.17 mm²/h. The hydrogel dosimeter exhibits considerable potential for use in dose verification applications.     

Process control and dosimetry in a multipurpose irradiation facility

Availability of the multipurpose irradiation facility at the Philippine Nuclear Research Institute has encouraged several local industries to use gamma radiation for sterilization or decontamination of various products. Prior to routine processing, dose distribution studies are undertaken for each product and product geometry. During routine irradiation, dosimeters are placed at the minimum and maximum dose positions of a process load.     

Non-disturbing thermoacoustic dosimetry of electron and bremsstrahlung beams

The thermoacoustic response of thin targets (TTs) to pulsed electron/gamma irradiation is analyzed in the context of determination of the radiation characteristics. Basic equations of thermoacoustic dosimetry linking thermoacoustic stress amplitude to deposited energy density are presented. Using these equations, it is possible to restore the particle distribution in the pulsed beam from the thermoacoustic response of one-dimensional (wire, rod) or two-dimensional (film, plate) TTs. Generation coefficients for the TT-based dosimeters are presented. The construction and principles of operation of thermoacoustic TT-based dosimeters for determination of the characteristics of pulsed electron beams are considered. The availability of thermoacoustic gamma dosimetry is analyzed. Specific features and merits of the method of thermoacoustic dosimetry are discussed.