Accidental and retrospective dosimetry using TL method

Retrospective dosimetry is one of the most important tools of accidental dosimetry for dose estimation when dose measurement was not planned. In the affected area many objects can be applied as natural dosimeters. The paper discusses our recent investigations on various electronic components and common salt (NaCl) having useful thermoluminescence (TL) properties. Among materials investigated the electronic components of cell phones seem promising for retrospective dosimetry purposes, having high TL responses, proper glow curve peaks and the intensity of TL peaks vs. gamma dose received provided nearly linear response in the dose range of 10 mGy–1.5 Gy.     

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.     

Effects of different matrixes on the dosimetric response of α-terthiophene films from the kGy to MGy range

Films of polymethylmethacrylate (PMMA) and polystyrene (PS) containing α-terthiophene (3T) undergo a radiochromic effect when exposed to electrons and gamma rays. The films turn either red–green or red, due to the formation of oligomeric radical cations. In both matrixes, absorbance at 465 nm grows linearly with dose when α-terthiophene concentration reaches 12%. Explored range goes up to ∼2×10⁶ Gy, with dose rates spanning over three orders of magnitude. Concerning their application as dosimeters, a higher sensitivity characterises the 3T–PMMA moiety, suggesting its suitability from the kGy range up to 1 MGy. Above this value films become fragile. 3T–PS films are less sensitive, but more radiation resistant. Therefore they better suit the medium-to-high dose dosimetry range. Dose rate influences the response sensitivity in a complex way, however above 80 and up to 3.6×10⁴ Gy/min an approximate linearity exists between log(dose rate) and sensitivity, as in the analogous cellulose triacetate system.     

Powder state alanine ESR dosimeter for measuring the absorbed dose of electron beam

This paper describes the application of powder state alanine/ESR dosimeter for measurement of the absorbed dose of electron beam, for transfer the dose standards and for quality controls of the products processed by electron beam irradiation.The dosimeter is a sealed plastic container containing pre-treated alanine powder. Spectra of the internal standard and the alanine sample are measured simultaneously by using dual - cavity of a ESR spectrometer. The internal standard is a CuCl₂. 2H₂O monocrystal which gives stable ESR signals. A diamond sample is regard as working standard. With these two standards, the measurement accuracy can be improved apparently. The standard dose value is determined with a electron beam calorimeter made in our laboratory for dose calibration purpose.The advantages and the dosimetry characteristics of the application of powder state alanine/ESR dosimeters are discussed. This method is proved accurate and easy to use. In the region of 10-10⁴Gy, the dose response show a linear relationship and the precision is better than ± 2%.     

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.     

A genipin-gelatin gel dosimeter for radiation processing

Genipin, a fruit extract from Gardenia jasminoides Ellis, forms cross-links in solutions of gelatin, to form a blue hydrogel that bleaches quantitatively upon irradiation and the colour change can be measured with a spectrophotometer. With the addition of sulphuric acid this dosimeter is sufficiently sensitive for quality assurance of radiotherapy level dosimetry. Without sulphuric acid the gel has a reduced sensitivity and responds linearly with dose between 100 and 1000 Gy, making it potentially useful as a dosimeter for radiation processing applications such as the phytosanitary irradiation treatment of food. We investigated the dose response characteristics of this new formulation and found that the darker gels are more sensitive to dose and have a reduced uncertainty.     

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.     

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.     

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.     

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.     

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.     

Radiochromic film containing methyl viologen for radiation dosimetry

Poly(vinyl alcohol) (PVA) films containing methyl viologen (MV²⁺) that colours blue upon exposure to ionizing radiation were investigated as possible dosimeters for use in radiation processing applications. In order to find the most suitable composition of the PVA-MV²⁺ film, different concentrations of the dye have been studied. The absorbance values at selected wavelengths, obtained from irradiation of the PVA film containing the most suitable MV²⁺ concentration, can be satisfactorily related to the absorbed dose over a wide range, from 50 Gy up to 40 kGy. The effects of dose, dose rate, humidity and temperature on the response of the PVA-MV²⁺ dosimeter film have been studied under laboratory conditions. We conclude that the PVA film containing MV²⁺ is a promising tool for the absorbed dose measurements in several industrial applications of ionizing radiations.     

Optimization of the sensitivity and stability of the PRESAGE™ dosimeter using trihalomethane radical initiators

The aim of this study is to investigate the effect of trihalomethane radical initiators on the radiological properties, radiation dose sensitivity and post response photo-stability of the PRESAGE dosimeter. Different PRESAGE dosimeters containing 50 and 100 mM of iodoform (CHI₃), bromoform (CHBr₃) or chloroform (CHCl₃) radical initiators where fabricated and irradiated with 6 MV photons for a range of radiation doses from 0 to 30 Gy. A comparison between sensitivity and radiological properties of the PRESAGE dosimeters with the different radical initiators was carried out. Optical density changes of the dosimeters before and after irradiation were measured using a spectrophotometer. The incorporation of different radical initiators in the composition of the PRESAGE dosimeter resulted in variation of the radiation dose sensitivity and radiological properties of the dosimeters depending on the type and concentration of the radical initiator used, with iodoform showing the highest dose-response slope followed by bromoform and chloroform. However, at 100 mM iodoform, the effective atomic number was significantly higher than water (Z_eff=16). This enhancement in dose-response was found to be directly related to the carbon–halogen bond dissociation energy and to the radiological properties of each individual radical initiator used in this study. Furthermore, the post-response stability of the PRESAGE dosimeters over two weeks remained stable regardless of the trihalomethane radical initiator employed, with negligible change in the post-response stability and linearity of the PRESAGE dosimeters.     

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.     

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.     

Magnesium lactate mixed with EVA polymer/paraffin as an EPR dosimeter for radiation processing application

The dosimetric characteristics of γ-radiation-induced defects in magnesium lactate (ML) rods (3.5 mm×10 mm) formulated by mixing ML with molten mixtures of paraffin wax and EVA copolymer have been investigated using electron paramagnetic resonance (EPR). The EPR spectrum of irradiated ML rods was characterized by a quartet signal with the spectroscopic splitting g-factor of 2.0048±0.0003 at 0.4 mT. The useful dose range of the rod dosimeter was 100 Gy to 80 kGy. The mass attenuation coefficient, μ/ρ, and the mass energy-absorption coefficient, μ_en/ρ, versus energy in the range of 10 keV to 20 MeV indicate that the prepared ML dosimeter is typically adipose tissue equivalent overall this energy range. The overall combined uncertainties (at 2σ) associated with routine dose monitoring in the dose range of 0.1–10 kGy and 10–80 kGy were found to be 6.14% and 6.36%, respectively.     

Generic phytosanitary irradiation treatments

The history of the development of generic phytosanitary irradiation (PI) treatments is discussed beginning with its initial proposal in 1986. Generic PI treatments in use today are 150 Gy for all hosts of Tephritidae, 250 Gy for all arthropods on mango and papaya shipped from Australia to New Zealand, 300 Gy for all arthropods on mango shipped from Australia to Malaysia, 350 Gy for all arthropods on lychee shipped from Australia to New Zealand and 400 Gy for all hosts of insects other than pupae and adult Lepidoptera shipped to the United States. Efforts to develop additional generic PI treatments and reduce the dose for the 400 Gy treatment are ongoing with a broad based 5-year, 12-nation cooperative research project coordinated by the joint Food and Agricultural Organization/International Atomic Energy Agency Program on Nuclear Techniques in Food and Agriculture. Key groups identified for further development of generic PI treatments are Lepidoptera (eggs and larvae), mealybugs and scale insects. A dose of 250 Gy may suffice for these three groups plus others, such as thrips, weevils and whiteflies.     

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.     

Formation of radical cations and dose response of α-terthiophene-cellulose triacetate films irradiated by electrons and gamma rays

The radiation-induced UV-vis spectrum of α-terthiophene radical cation in solid is reported. The radical cation initiates an oligomerization in the CTA matrix producing permanently coloured conjugated polarons. The specific net absorbance at 465 nm is linearly related with dose up to 2×10⁶ Gy, for electrons and gamma irradiation. The decrease of the UV typical absorption (355 nm) and of four IR bands of α-terthiophene is linear with dose, as well. Although sensitivity is influenced by dose rate, it turned out that a linear relationship holds between sensitivity and log dose rate, in the range from 2 to 10⁵ Gy/min. These findings suggest a potential application of the system for dosimetric purposes over a wide range of dose and dose rate.     

Temperature effects on egg shells investigated by XRD,IR and ESR techniques

Samples of egg shell powder were annealed in air in the temperature range 298–1173 K. Samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electron spin resonance (ESR). ESR measurements were made on annealed egg shells before and after gamma irradiation at 4 kGy. Annealing egg shells produced a range of organic radical with g-values from g=2.005 to 2.002. The thermal dependence of this signal may provide valuable information about the extent of the thermal treatment that the sample was subjected to. Samples irradiated from 3Gy to 10 kGy were analyzed by ESR in order to obtain the response curve and to show ESR signal behavior.