EPR study of table sugar rod and powder as high dose dosimeters

In order to improve the ease of sample handling, the reproducibility of signal detection and quantification, simple methods of incorporating a homogeneous mixture containing sugar powder (30%) with wax (35%) and rubber (35%) into rods has been adopted. The dose response, the time stability of the free radicals produced in table sugar dosimeters (in both rod and powder form) by gamma radiation and the effect of the temperature during irradiation were studied by EPR (Electron Paramagnetic Resonance). The peak-to-peak height (PPH) measurement of the EPR signal is studied as a function of the absorbed gamma dose in the range 0.1–58 kGy. For the two forms, a linear dependency is found between 0.1 and 26 kGy. At higher doses the EPR signal amplitude continues to grow but non-linear up to 58 kGy. The dependence of temperature during irradiation has been investigated in the temperature range 25–40 °C and the calculated correction coefficients were found (2.7 ± 0.2)% °C^?1 and (1.5 ± 0.3)% °C^?1, respectively, for powder and rod forms. The time stability of the stored sugar samples was investigated for 34 days at room temperature, a rapid decrease of EPR signal was showed immediately after irradiation followed by slowly decrease.     

TL and EPR studies of CaSO4:Dy phosphor to investigate its efficacy in measurement of food irradiation dose at sub-ambient temperatures

The effects of sub-ambient temperatures of irradiation and dose response of CaSO₄:Dy phosphor was investigated. The irradiation dose in the range 0.5–7.0 kGy was chosen to meet the requirement of commercial food irradiation at low temperature. Commercially available phosphor showed no significant change in glow curve structure with low temperature of irradiation. In order to enhance the sensitivity of the low temperature glow peak (142 °C), the phosphor was subjected to different post-preparation thermal treatments at 700–900 °C. The change in glows and improvement in dose response characteristics were explained by Electron Paramagnetic Resonance (EPR) spectroscopy. At sub-ambient temperature of irradiation, the behavior of thermally treated CaSO₄:Dy phosphor with increasing dose revealed improved linear response of the low temperature glow peak and could be an efficient dosimetry system for the food commodities irradiated at low temperatures.     

Photostimulated luminescence of corrugated fiberboard as an additional screening method for detecting radiated foods

In this study, PSL of non-irradiated and irradiated corrugated fiberboards (CFs) was investigated to evaluate the possibility that CFs can be used as alternative specimens for the screening detection method of food irradiation. The irradiation at a dose of only 0.15 kGy increased PSL signals of the CF over 1 order of magnitude. The PSL signals increased with increasing in gamma irradiation dose and became almost saturated at a dose of 5 kGy. The core of CFs showed PSL signals sufficient for distinguishing irradiated from non-irradiated at least 6 months after irradiation even though the CF was exposed to light and the environmental temperature increased to 50 °C. These results suggest that the PSL property of the core of CFs is useful for detecting irradiation. However, the large variation of PSL signals among CFs made it difficult to set a well-defined “positive” threshold limit to distinguish irradiated from non-irradiated completely. All of the non-irradiated CFs showed PSL signals above 10³ counts, which is much higher than that detected for foods. It is apparent that the threshold limit of EN 13751 is not applicable to detecting irradiated CFs. More detailed collaborative research with large number of samples is needed to establish new threshold limits involving “intermediate” classification.     

Usability of tartaric acid in dose measurements: an ESR study

Unirradiated tartaric acid samples do not exhibit any ESR signal. However, the ESR spectra of irradiated samples contain many resonance signals. The dose–responce curves of the resonance signals, denoted as I ₁, I ₂, I ₃ and I ₄ in the present study, were found to increase linearly with the applied radiation dose in the range of 0.04–25 kGy. Adjusting the microvawe power and modulation amplitudes of 1.0 mW and 1.0 mT, respectively, was found to increase the sensitivity of tartaric acid. From the dose–response curves and room temperature decay data, it was concluded that the I ₃ resonance signal of tartaric acid can be used for dose measurements at intermediate (0.04–0.4 kGy) and high dose (0.5–25 kGy) levels.     

Investigation of the optical absorption characteristics of slow-cooled LiF:Mg,Ti (TLD-100)

The optical absorption (OA) spectrum of LiF:Mg,Ti has been studied as a function of dose at two different cooling rates following the 400 °C pre-irradiation anneal in order to further investigate the role of cooling rate in the thermoluminescence (TL) mechanisms of this material. “Slow-cooling” following the pre-irradiation 400 °C anneal substantially decreases the OA bands at 3.25 eV and 4.0 eV, in agreement with the overall loss in TL peaks 2–5 intensity using slow-cooling routines. Slow-cooling appears to shift the maximum intensity of peak 5 to lower temperatures (a behaviour which has been attributed to an enhanced intensity of peak 5a), however, no difference in the shape of the 4.0 eV OA band is detected following “slow-cooling”. Apparently the OA band related to peak 5a is too close in energy to the peak 5 OA band to be observed due to lack of sufficient resolution and spectral deconvolution process or it is not present at room temperature (RT) and formed during heating of the sample. The intensity of the 4.0 eV OA band does not change if the sample (prior to irradiation to a standard dose of 200 Gy) is irradiated to 4 kGy followed by a 500 °C/1 h post-irradiation anneal. This result demonstrates that the loss of intensity at high levels of dose (so-called radiation damage) of TL glow peak 5 results from alteration of the LCs or to the creation of additional competitive centers and is not correlated with the dose behaviour of the TCs.     

A radiochromic film based on leucomalachite green for high-dose dosimetry applications

A colorless polyvinyl butyral film (PVB) based on radiation-sensitive dye of leucomalachite green (LMG) was investigated as a high-dose dosimeter for gamma radiation processing applications in the dose range of 3–150 kGy. The useful applications for such dose range are food irradiation treatment, medical devices sterilization and polymer modification. Gamma irradiation of the film induces a significant intensity of green color, which can be characterized by a main absorption band at 627 nm and a small band at 425 nm. The variation in response of irradiated film stored in the dark and under laboratory light illumination was less than 3% during the first 6 days of storage. The response of film during irradiation was slightly influenced by relative humidity in the range of 12–76%; however, it was significantly affected by temperature in the range of 5–40 °C. The radiation chemical yield was reported to be 6.76 × 10⁻⁶ mol/J at the absorbed dose of 30 kGy for the film containing 6.5% of LMG dye. The overall uncertainty associated with routine dose monitoring would be less than 6% at a 95% confidence level if the dosimeter was being corrected for irradiation conditions and being calibrated with reference standard dosimeter in the production facility.     

Thermoluminescence and optically stimulated luminescence studies on LiMgPO4 crystallized by micro pulling down technique

LiMgPO₄ (LMP) crystals were grown by micro pulling down technique. Samples were irradiated with different β-particle doses of the ⁹⁰Sr/⁹⁰Y source. Thermally and optically stimulated luminescence spectra were measured with the automatic Risø TL/OSL-DA20 reader under the different modes of stimulation. The dose–response dependence, reproducibility, the lowest measurable dose and short-time fading were investigated. TL and OSL dose–response of LiMgPO₄ crystals was found to be linear up to around 1 kGy, what makes this material suitable for high dose measurements. Discrepancies between successive measurements did not exceed 10%, regardless of the applied growth parameters. The lowest measurable dose, defined as three standard deviations of the signal of unexposed detector, was determined around 0.5 mGy. About 73% of the initial OSL signal value was measured 24 h after the irradiation. For longer periods of time the level of signal stabilizes so that there was no further loss of signal observed. In case of TL, the level of signal does not stabilize and decreases to 69% within 2 weeks after the irradiation. The obtained results tend to suggest that LiMgPO₄ crystals may be considered as promising dosimeters for both personal and high dose dosimetry.     

Feasibility of radiation sterilization and dosimetric features of ampicillin: an electron spin resonance study

In the present work, it was aimed to identify radical species produced by gamma irradiation (3–34?kGy) of solid ampicillin, to determine its spectroscopic, dosimetric, stability and kinetic behavior, and to investigate feasibility of the radiation sterilization feature of ampicillin by using electron spin resonance (ESR) spectroscopy. ESR experiments were performed at low and high temperatures (130–400?K) to examine the characteristic properties of the radical intermediates that are produced in ampicillin by gamma radiation treatment. Unirradiated ampicillin presented no ESR signal but irradiated samples exhibited ESR spectra with four resonance peaks spread over a magnetic field range of 8?mT. The spectral parameters of the central resonance line of the spectrum are g?=?2.0044 and ΔH_pp?=?0.08?mT. An exponential growth function of the applied dose was found to describe best the experimental dose–response data and it was found that ampicillin did not exhibit the feature of a good dosimetric material as its ESR intensity was relatively weak even for the samples irradiated at high level of doses. G_mean value of gamma-irradiated ampicillin was found to be 4.6?±?0.9?×?10^?9?mol/J, which is very small compared to irradiated alanine solid sample. However, the discrimination of irradiated ampicillin from unirradiated one was possible even ～3 months after storage at normal conditions. The simulation calculations indicated that gamma irradiation created two different radical species in solid ampicillin. Decay activation energy of the radical species which is mostly responsible from central intense resonance line is calculated to be 55.6?±?3.2?kJ/mol by using the signal intensity decay data derived from annealing studies. It was concluded that ampicillin could be sterilized by gamma radiation and ESR spectroscopy can be used as a potential technique to monitor its radiosterilization process.     

Electron beam induced modifications in crystalline structure of polyvinylidene fluoride/nanoclay composites

PVDF/nanoclay nanocomposites were prepared via melt mixing method. The intercalated dispersion of the nanoclay in PVDF matrix was confirmed by XRD. According to FTIR, DSC and XRD results, the presence of nanoclay facilitated transition from α-to-β crystalline phase. Electron beam irradiation decreased the melting point of the nanocomposites. The decrease in melting point of the nanocomposites was about 11 °C at 500 kGy. The crystallinity of nanocomposites increased at an irradiation dose of 100 kGy and decreased at higher irradiation doses. The extent of crosslinking of the nanocomposites increased significantly with irradiation up to 300 kGy. The nanoclay intensified the increase in yield strength with irradiation doses up to 300 kGy. The combination of nanoclay and irradiation had a synergistic effect on the increase of yield strength.     

Development of dry polymer electrolyte based on polyethylene oxide with co-bridging agent crosslinked by electron beam

Polyethylene oxide (PEO)-based electrolytes were crosslinked using electron beam (EB) irradiation. The gel contents of a polymer film were increased after irradiation doses of 0, 140, 280, and 420 kGy, with ionic conductivities of 0.831, 1.55, 6.08, and 7.95 (× 10^? 5) S cm^? 1 at 40 °C, respectively. The slight decrease in conductivity at higher temperatures after irradiation is due to the retardation of polymer motion by crosslinking. The electrolyte with higher EB dose amount exhibits higher conductivity due to stabilization of the amorphous state. The EB crosslinking with a co-bridging agent shows enhanced conductivities of 4.71, 6.59, and 7.18 (× 10^? 5) S cm^? 1 at 40 °C, after irradiation with 140, 280, and 420 kGy. Addition of the co-bridging agent is effective for developing a crosslinked structure with a smaller EB dose. Tensile strength becomes two to three times higher with irradiation compared to the non-treated polymer. Combination of the EB technique with a co-bridging agent is a simple and effective method to prepare strong dry polymer electrolyte films with improved room temperature conductivity.     

Uncertainty and routine use of Aerial l-alanine – Electron spin resonance dosimetry system

Aerial l-alanine pellet dosimeter is characterized by MiniScope MS300 electron spin resonance spectrometer measurements using Aer'EDE Version 2.0.4. software for dose calculation. The measurement traceability is achieved by Aerial dosimetry laboratory where dosimeters for calibration curve were irradiated by electron beam accelerator. Dose determinations in Aerial are traceable to National Physical Laboratory (NPL). The software used for construction of calibration curve gives also the standard deviation of the residuals of measurements for calibration that is used for dose uncertainty calculation. In aim to determine whether this value can actually be taken as absorbed dose uncertainty during usage of this dosimetry system, alanine dosimeters were irradiated with doses between 5 and 32 kGy by ⁶⁰Co laboratory source for internal calibration. The dose rate at the places for irradiation was (20 ± 0.5) mGy s⁻¹ determined by Fricke dosimeter. Measurement of each irradiated dosimeter was repeated ten times in ten days. The results of measurements were analyzed to identify the sources of uncertainty, as well as their quantification in evaluation of total measurement uncertainty. In addition to statistical effects, the very low dose rate that was used for the irradiation of alanine dosimeters affects the measurements of absorbed dose, particularly for higher absorbed doses where the measured dose can be up to 3% lower than the real.     

Radiation sensitivity and dosimetric features of sultamicillin tosylate: an electron spin resonance study

Particular interest now centers on the preparation of sterile unit-dose preparations. When preparations are purified from microorganisms using classic sterilization techniques, serious degradations may occur, especially in temperature sensitive drugs and drug active components. Sultamicillin is the tosylate salt of the double ester of sulbactam plus ampicillin. Sultamicillin (SULT) tosylate has previously been shown to be clinically and bacteriologically effective in a variety of infections. The use of high-energy radiation, such as gamma rays, for the sterilization of pharmaceuticals offers considerable interest because of the clear advantages this process has compared with other methods of sterilization. However, radiosensitivity of irradiated pharmaceuticals is important in this respect. Thus, radiosensitivity of SULT and its potential use as a dosimetric material were investigated by electron spin resonance (ESR) spectroscopy in the present work. Samples of SULT powder were irradiated at doses of 3, 6, 10 and 15 kGy and ESR spectra were recorded at room and at different temperatures. Variations of different spectroscopic parameters with irradiation dose, temperature and storage time were evaluated using data derived from experimental ESR spectra which exhibited five different resonance peaks. Stabilities of the radiolytic intermediates at high temperatures were also investigated through annealing studies performed at 340, 345 and 350 K. Rapid decreases in resonance peak heights above 325 K were considered a manifestation of the unstable character of the radiolytical intermediates at high temperature, although they decayed relatively slowly at room temperature. Seven different mathematical functions have been tried to fit the experimental dose–response data, and a power function of the applied dose was found to describe best the dose–response data.     

Thermoluminescence in two varieties of jadeite: Irradiation effects and application to high dose dosimetry

The thermoluminescence properties of white (WJ) and green (GJ) mineral jadeite have been investigated with a view to be of use in high dose dosimetry. WJ presented glow curve with 110, 190 and 235 °C peaks. All these peaks grow with radiation dose. The glow curve of GJ the green variety has TL peaks at 140, 210, 250 and 330 °C. We also observed that there is a difference between the TL glow curves for both samples, irradiated with gamma and electron. As expected the green jadeite can be used for measurement of dose as high as 50 kGy.     

The Chain Segment Motion and Traps in γ‐Irradiation Crystalline Nylon 1010

The chain segment motion, charge trapping and detrapping in γ‐irradiated nylon 1010 films (doses in the range 0–2,000 kGy were used) have been investigated by means of thermally stimulated depolarization current (TSDC). There are three current peaks (named α, ρ₁ and ρ₂, respectively) in the TSDC spectra, corrected by spontaneous current, above room temperature. By analyzing the characteristic parameters of the three peaks, it is found that the chain segment motion in the amorphous regions becomes more difficult at low irradiation dose (<100 kGy) and then becomes easier with further increasing irradiation dose. The stability of the traps at the crystalline‐amorphous interfaces increases at low irradiation dose (<500 kGy) and then decreases with further increasing irradiation dose; the irradiation promotes the creation of traps and the stability of traps in the crystalline regions.     

Spectral characteristic of high-dose high-temperature emission from LiF:Mg,Cu,P (MCP-N) TL detectors

High-temperature emission spectra of LiF:Mg,Cu,P (MCP-N) TL detectors, irradiated above the nominal saturation level, up to the hundreds of kGy, have been measured. Emission spectra integrated over the whole temperature range, as well as the spectra recorded at the temperatures corresponding to the TL peaks maxima, were analyzed. With increasing dose of γ-radiation no significant changes were observed in the short wavelength emission range (220–450 nm) of the measured spectra. For doses of 4 kGy and higher the long wavelength emission (450–800 nm) started to be visible. All recorded spectra have been expressed in a form of the sum of several Gaussian-shape bands in the energy domain, which parameters remain in a general agreement with the measurements of Mandowska et al. (2010). Spectra of the low-temperature, main, high-temperature and “B” TL peaks were investigated. In the ranges of the low-temperature and the main dosimetric peaks, that is 100–125 and 210–230 °C, respectively, the short wavelength emission disappeared with increasing dose and for the highest doses the long wavelength emission became dominant. Both the high-temperature (290–320 °C) and the “B” (370–425 °C) peaks emission spectra exhibited somewhat different behavior with increasing dose. Initially, an even growth of the whole spectrum was observed and for doses higher than 16 kGy the intensity of the spectrum decreased, but the short wavelength emission band fell significantly faster, in case of the high-temperature TL peaks. In case of the “B” peak emission spectra the long wavelength emission did not play any role in the analyzed dose range. The spectra measured at the TL peaks maxima were also fitted with several Gaussian-shape bands. Dose-intensity dependences for all Gaussian-shape bands fitted to the measured spectra are also included in this paper.     

Commercial pharmaceutical glass containers as probes for the post-sterilization dosimetry of liquid drugs

Drug sterilization with ionizing radiation is a well-established technology, which is gaining ground the last decades since it allows the adequate sterilization of heat-sensitive pharmaceutical preparations. In a previous study (Kazakis et al., 2015a), the possibility to identify irradiated liquid-state drugs by means of TL measurements on their glass containers was explored with very promising findings.The present work constitutes a continuation and extension of the previous work, employing additional TL measurements, along with new OSL measurements, on the same glass containers of two widely used liquid drugs, (Hexalen^® and Voltaren^®), for beta-doses up to 30 kGy, while an investigation of the presence of very deep traps (VDT), i.e., traps with their peak maximum temperature beyond the 500 °C, also took place.Results indicate that dose estimation, after the ionizing sterilization of a liquid drug, using the glass containers is possible in many ways. Both direct OSL and TL dose response can be fitted with a linear function for doses up to 6 kGy and 14 kGy for Hexalen and Voltaren respectively. For higher doses, up to 30 kGy, the intensity continues to increase, though in a lower rate, and the response can be fitted with a linear function as well, indicating that no saturation is reached. Presence of VDT is evident in both glasses with their thermally assisted OSL (TA-OSL) and subsequent photo-transferred residual TL (RTL) dose response exhibiting linear behavior in two distinctive dose areas. In any case, no saturation of the VDT is observed for doses up to 25 kGy. The above is very important, since it would allow the estimation of the sterilization dose even if the glass container has been exposed to light or heated to temperatures up to 500 °C.Thus, all findings are very promising and support the idea of using the glass containers of commercial liquid drugs as probes for the post-sterilization dosimetry of these drugs and for normal and/or accidental dosimetry.     

The study of gamma irradiation effects on poly (glycolic acid)

We have investigated the effects of gamma irradiation on chemical structure, thermal and morphological properties of biodegradable semi-crystalline poly (glycolic acid) (PGA). PGA samples were subjected to irradiation treatment using a ⁶⁰Co gamma source with a delivered dose of 30, 60 and 90?kGy, respectively. Gamma irradiation induces cleavage of PGA main chains forming ～O?H₂ and ?H₂COO～ radicals in both amorphous and crystalline regions. The free radicals formed in the amorphous region abstract atmospheric oxygen and convert them to peroxy radicals. The peroxy radical causes chain scission at the crystal interface through hydrogen abstraction from methylene groups forming the ～?HCOO～ (I) radical. Consequently, the observed electron spin resonance (ESR) doublet of irradiated PGA is assigned to (I). The disappearance of the ESR signal above 190°C indicates that free radicals are formed in the amorphous region and decay below the melting temperature of PGA. Fourier transform infrared and optical absorption studies confirm that the groups are not influenced by gamma irradiation. Differential scanning calorimetry (DSC) studies showed that the melting temperature of PGA decreased from 212°C to 202°C upon irradiation. Degree of crystallinity increased initially and then decreased with an increase in radiation as per DSC and X-ray diffraction studies. Irradiation produced changes in the physical properties of PGA as well as affecting the morphology of the material.     

Space-selective modification of the magnetic properties of transparent Fe3+-doped glass by femtosecond-laser irradiation

We have demonstrated spatially selective modification of the magnetic properties of transparent iron-oxide-doped glass by femtosecond- (fs-) laser irradiation and subsequent annealing. A near-infrared fs-laser beam with a wavelength of 775 nm was focused 1 mm below the surfaces of glass samples. This produces absorption peaks due to the formation of hole-trap centers in the irradiated region. Transparency was recovered after annealing at 450°C. A ferrimagnetic component was observed in the M–H curve even at room temperature, whereas the diamagnetic component dominated in the M–H curve of the as-prepared glass sample. This indicates that fs-laser irradiation enhanced the magnetization in the irradiated area. The irradiated and annealed glass sample also exhibited superparamagnetic blocking in the temperature dependence of the magnetization with a blocking temperature higher than room temperature. This change in magnetism is presumably due to local crystallization of ferrimagnetic nanoparticles, such as magnetite, induced by fs-laser irradiation and annealing. The magnetic and optical properties of glass that had been annealed but not irradiated by a fs-laser beam remained unchanged.     

Leuco crystal violet/poly(vinyl butyral) thin film as a high-dose dosimeter

A polyvinyl butyral film incorporating a radiochromic leuco crystal violet dye (LCV) and a UV-absorber of tinuvin-P has been investigated as a high-dose dosimetry for ⁶⁰Co radiation processing in the dose range of 1–100 kGy. Upon γ-ray exposure, the prepared film undergoes visual color change to deep purple color characterized with an absorption band peaking at 594 nm with a shoulder around 552 nm. The response of films stored in dark place at room temperature overall a period of 55 days exhibited good stability, that the increase in response of irradiated and unirradiated films did not exceed 2% and 4%, respectively overall this storage period. The results indicate that no further protection of films from laboratory fluorescent light during the measurement of irradiated film is required. The effect of temperature and relative humidity on the performance of film during irradiation and the overall uncertainty associated with absorbed dose monitoring were investigated in the present study.     

Characterization of deep energy level defects in α-Al2O3:C using thermally assisted OSL

Commercially available α-Al₂O₃:C powder was studied for deep energy level defects by a newly suggested method using thermally assisted optically stimulated luminescence (TA-OSL) phenomenon. The method involves simultaneous application of continuous wave optically stimulated luminescence (CW-OSL) as well as thermal stimulation up to 400 °C, using a linear heating rate of 4 K/s. By using this method, two well-defined peaks at 121 °C and 232 °C were observed. These TA-OSL peaks have been correlated to two different types of deeper defects which can be bleached at 650 °C and 900 °C respectively on thermal treatment. These deeper defects, having larger thermal trap depth and relatively lower photoionization cross-section at room temperature for stimulation with blue LED (470 nm), are stable up to 500 °C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or temperature. As only a fraction of signal is bleached during TA-OSL readout, multiple readouts could be performed on an exposed sample using this technique. The dose vs TA-OSL response from deep traps of α-Al₂O₃:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry. The value of thermally assisted energy (E_A) associated with these traps in α-Al₂O₃:C has been determined to be 0.268 eV and 0.485 eV respectively and the corresponding values of photoionization cross-section at room temperature (25 °C), for optical stimulation with blue light (470 nm), are 5.82 × 10^?20 and 3.70 × 10^?22 cm², respectively. The process of thermally assisted OSL has been formulated analytically as well as theoretically for describing the temperature dependence of optical cross-section and evaluation of thermally assisted energy associated with deep traps.