Post-irradiation Stability Research Articles

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.

The suitability of a dyed plastic film for biologically effective UVB radiation measurement

A thin dyed plastic film (thickness, 0.08 mm) was developed and found to be suitable for use as a personal dosimeter for biologically effective solar UVB and UVC radiation. The dosimeter film was fabricated by casting an aqueous solution of poly(vinyl alcohol) and a mixture of colourless hexahydroxyethyl pararosaniline cyanide dye (HPR-CN) and sandolan yellow N-3GL dye (Acid Yellow 75). This flexible plastic film undergoes a colour change from yellow to blue on UV irradiation. The radiation-induced colour was analysed spectrophotometrically at the maximum of the absorption band peaking at 602 nm. The absorption spectra, dose response, dose rate effect, spectral sensitivity and post-irradiation stability of the film dosimeter are discussed. The maximum sensitivity of this new film lies between 280 and 315 nm, in the erythemal region, where most acute and chronic effects of sunlight exposure on biological systems are believed to occur.

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.

Post-irradiation stability of response of an aqueous coumarin dosimeter

Aqueous solution of coumarin (α-benzopyrone) has been evaluated spectrophotometrically as a γ-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.

The Use of Sugar Pellets in ESR Dosimetry

Table sugar (sucrose) is a convenient, common, tissue-equivalent material suitable for electron spin resonance (ESR) dosimetry of ionising radiation. The simple free radical signal in irradiated sugar is stabilised if the sugar is made into pellets using an inert silicone elastomer (Dow Corning 732). Such pellets, which offer greater convenience and signal stability and reproducibility, have been prepared and tested for their radiation response, sensitivity and post-irradiation stability. Irradiated sugar is detectable at ≥0.1 Gy, the signal intensity is linear with dose, and the fading of the signal, post-irradiation, is minimal for samples kept under ambient conditions

The gamma-ray response of clear polymethylmethacrylate dosimeter radix RN15®

Basic characteristics of different batches of Radix RN15® dosimeter, a commercially available undyed polymethylmethacrylate dosimeter, was studied for its application to process control of radiation sterilization. Radix has relatively small deviation of thickness, optical absorption spectrum, and optical density values before irradiation. The response curves, in terms of net optical density per unit thickness (ΔOD/mm) as a function of absorbed dose, D PMMA, are nearly linear up to 15 kGy and become sublinear at higher doses. Scattering of dose response in 5 dosimeter replicates is ± 1% (1 σ). The dose-response slope at 25 kGy while held at irradiation temperatures in the range 0–60°C, relative to those under 25°C, increases with temperature up to 40°C, the maximum point, and decreases at higher temperatures. Over the temperature range of 10–50°C, the variation with temperature of evaluated dose derived from the calibration curve at 25°C is less than 5% when using a dose rate of 6 kGy/h. At lower dose rates (e.g. 0.7 kGy/h) the irradiation temperature dependence is negligible over this temperature range. The temperature dependence at 40 kGy is less severe than that at 25 kGy. The post-irradiation stability of dose response is less than 5% for more than 100 h after 25 kGy irradiation and storage at 0–35°C. The change in optical density of unirradiated dosimeters 3 years after manufacturing is negligible when the dosimeters are stored at controlled laboratory conditions of temperature (25°C) and relative humidity (40%). The 3-year-old dosimeters by irradiation to a dose of 25 kGy show about 2% lower response than that at 25 kGy at the beginning of the 3-year period.

Fading characteristics of an alanine-polystyrene dosimeter

Alanine dosimetry is useful for transfer dosimetry by long distance mailing, because of its stability. It has the advantage that the measurement of electron spin resonance (ESR) spectral signal is non-destructive to the dosimeter, with the promise that the method may supply archival dosimetry data, depending on the degree of post-irradiation stability of the signal. The effects of temperature during irradiation and storage on fading of the ESR signal were studied using an alanine dosimeter molded with polystyrene (alanine-PS dosimeter). This investigation covered a long range of storage time (up to 160 days) after irradiation to absorbed doses in the range 1 to 100 kGy, for application to transfer dosimetry between Japan and neighboring Asian countries. Dose response of an alanine-PS dosimeter depends on the temperature during irradiation. The same temperature coefficient of +0.24%/°C was measured at different dose levels of 1, 10 and 100 kGy administered at a constant dose rate of 7 kGy/h. Fading of the dose response was measured under storage at various temperatures (5–40°C). The fading curve generally has two phases with fast and slow fading rates. The response of an alanine dosimeter is relatively stable for doses of 1.4 and 14 kGy, when stored at temperatures below 25°C. However, the degree of fading was roughly 3 and 5% under a storage temperature of 40°C for 5 and 100 days, respectively, after irradiation to 14 kGy. The fading percentages at 100 kGy were 2 and 4% (after 5 days) and 6 and 15% (after 100 days) under the storage temperature of 25 and 40°C, respectively. The fading rates have a relatively small dependence on irradiation temperature. This is observed even when irradiation are made at high temperatures (60°C) and for the doses 100 kGy and above. The mechanism of decay of radicals is discussed to explain the fading characteristics of the two phases of fading. The alanine-PS dosimeter is useful for transfer standard dosimetry up to a dose level of 10 kGy when stored after irradiation at temperature below 40°C. However, consideration of temperature effects during and after irradiation is vital for accurate transfer dosimetry of high doses, especially in the southern Asian countries.

Post-irradiation degradation of polypropylene: Comparison of hindered aromatic phenole and amine as gamma-stabilizer—I

Post-irradiation stability of 60Co-γ-ray irradiated isotactic PP has been studied at 25 and 50 kGy. The effectiveness of 2,6-di-tert-butyl-p-cresol (BHT) and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) at various concentrations is compared. The variation of crystallinity, carbonyl and hydroxyl index, mechanical properties, of stabilized and unstabilized PP was followed for 6 months after irradiation. Although the percentage of crystallinity of the unstabilized samples increased upon irradiation, but for all stabilized ones not only the initial value was retained but remained constant and lower to that of the unstabilized samples during storage. Tensile strength and bend strength was also retained. The extent of chain scission has been followed by measuring the change in apparent viscosity (μ a) and flowability parameters, ( K) and ( n), using power law equation. Although both types of stabilizers were highly effective, the amine type imparts more stability at a longer time after irradiation as the corresponding nitroxyl and hydroxyl amine groups are formed.

Evaluation of a commercial red-dyed plastic film for gamma-radiation monitoring

The radiation response characteristics of the radiation-induced bleaching of a commercially available plastic film tinted with red colour are investigated, as well as pre- and post-irradiation stability. By spectrophotometry of this film, a wide range of absorbed doses may be measured (10–600 kGy). The new film monitor is flexible, rugged and stable on extended storage before and after irradiation, although there is some short-term instability in the first few days after irradiation. A computer program has been used for regression analysis of thickness and dye variations in the plastic film. The results indicate a relatively uniform distribution and homogeneity of dye and thickness in the plastic material. This thin (0.03 mm) dyed-plastic radiation monitor is widely available in large quantities and inexpensive, which makes it suitable for routine high-dose photon applications in radiation processing of materials.

The effect of impact modifier and of nucleating agent on the radiation tolerance of polypropylene

The effect of two types of additives were investigated with respect to the oxidative post-irradiation stability of polypropylene: SBS thermoplastic rubbers as impact modifiers and benzoic acid as nucleating agent. Testing was performed by ultimate deformation on bending. The thermoplastic rubber additive increased the post-irradiation stability of polypropylene substantially.

Radiation dosimetry using clear PMMA and PVC in the range of 5–45 kGy

Some plastic sheets manufactured or commercially available in Pakistan have been tested as radiation dosimeters for cobalt-60 γ-rays. Radiation induced colouration in the plastics have been measured spectrophotometrically. The results show that 2 mm thick clear poly(methyl methacrylate) (PMMA) can be used as radiation dosimeter up to 45 kGy when absorption measurements are made at 305 nm and 314 nm; whereas 1 mm thick clear poly(vinylchloride) (PVC) is useful up to 30 kGy when measured at 396 nm. The response of PMMA dosimeter is stable for at least 15 days and that for PVC for 30 days, when stored under ambient conditions after irradiation. Post-irradiation stability at various temperatures (−10 to 55°C) has also been studied.

Cellulose diacetate film dosimeters

The radiation response characteristics of commercially available cellulose diacetate and cellulose triacetate films tinted with various colors are investigated, as well as the effects of dose rate, humidity, temperature, and pre- and post-irradiation stability. By using more than one color of film, a wide range of absorbed doses may be measured (10 4 - 2 × 10 6 Gy) with negligible dose-rate dependence. The films are reproducible and stable on extended storage before and after irradiation. Their responses, however, are dependent on temperature and relative humidity during irradiation. The wide availability and low price make these dosimeters candidates both for high-dose electron and photon applications and as routine monitors and dose-mapping systems for radiation curing and processing of materials.

A spectrophotometric readout method for free radical dosimetry

An accurate and inexpensive spectrophotometric readout method is given for free radical dosimetry. The stable free radicals in irradiated alanine/glutamine powder, when dissolved in a solution containing ferrous ammonium sulphate and xylenol orange in 0.05 N H 2SO 4(FX), oxidize ferrous ions and the xylenol orange forms a complex with ferric ions produced in the solution. The absorbance of the complex is measured at 525 nm for alanine and at 540 nm for glutamine. The influence of various parameters, such as size of the container, weight of the powder dissolved, xylenol orange concentration, purity of distilled water, postirradiation stability and dose-rate dependence on the response of the dosimetric technique, has been investigated. It was found that the dosimetric response is independent of dose-rate. Alanine does not show any significant postirradiation fading. Irradiated glutamine powder is stable for about a month, the fading is less than 2% up to three months later, and it increases to only about 5% over a period of six months. The reproducibility of the method is better than ±2%, and it offers an alternative to ESR and lyoluminescence techniques for free radical dosimetry. A dose of 0.01 to 4 kGy can be measured with an alanine dosimeter and 0.1 to 100 kGy with a glutamine dosimeter. Empirical relationships between absorbance and dose are given.

The aqueous coumarin system as a low range chemical dosimeter

A chemical dosimetric system, aqueous coumarin, has been developed. The dosimeter can be used to measure doses in the range 10–6000 rad using fluorescence method and in the range 5–56 krad using optical absorption measurements. The energy dependence of this dosimeter was studied and it was found that the response decreases by about 9% at energies encountered in deep X-ray therapy as compared to its value for cobalt-60 gamma rays. However, at diagnostic X-ray energies (80 kV), the response is less by about 36%. The dosimeter is independent of dose rate up to about 100 rad min −1 but the response decreases as the dose rate is increased. It is independent of temperature during irradiation up to 29°C but the response slightly increases beyond this temperature. The dosimeter also shows good pre- and post-irradiation stability.

Color stabilization of poly(vinyl chloride) against high‐energy electron irradiation

AbstractColor stability in irradiated PVC may be achieved by (1) structural modification to block dehydrochlorination, (2) addition of radiation protectors, or (3) addition of radical scavengers. This study explores the latter approaches. Twenty‐six compounds representing a variety of structural types were screened for their effectiveness as measured by subsequent color development. Fifteen of the compounds imparted partial or complete postirradiation stability. Possible stabilizer mechanisms are discussed.

Post-Irradiation Stability of Some Properties of Cotton Cellulose

Post-Irradiation Stability of Some Properties of Cotton Cellulose