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Optically stimulated luminescence investigation of chicken bones towards their use at food post-sterilization and retrospective dosimetry
Applied Radiation and Isotopes 154 (2019) 108899
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: http://www.elsevier.com/locate/apradiso
Optically stimulated luminescence investigation of chicken bones towards their use at food post-sterilization and retrospective dosimetry Nikolaos A. Kazakis *, Nestor C. Tsirliganis Laboratory of Archaeometry and Physicochemical Measurements, R.C. ‘Athena’, P.O. Box 159, Kimmeria University Campus, 67100, Xanthi, Greece
A R T I C L E I N F O
A B S T R A C T
Keywords: Chicken Bones Hydroxyapatite Retrospective dosimetry Post-sterilization dosimetry Optically stimulated luminescence
The present work explores the luminescence behavior of animal bones and more specifically, chicken bones, using OSL in order to investigate whether they can be used for the dose assessment in the case of an accident or as dosimeters at the post-sterilization dosimetry of foods. Results indicate that the OSL sensitivity is rather low and the lower detection limit is ~18 Gy eliminating the possibility of using bones as emergency dosimeter. However, the OSL dose response is linear for doses up to ~1.0 kGy, while response over the entire dose range, up to several kGy, can be fitted with an exponential saturation curve. When bones are kept in dark, half of the initial OSL signal is lost seven days after irradiation, with no further loss for longer time periods up to two months post-irradiation. Since bones are heat-sensitive and exhibit sensitization, a dose recovery test was also conducted using the SARHS protocol in order to investigate if the protocol is capable of calculating the sterilization/accidental dose of irradiated chicken/poultry. The “unknown” doses were successfully recovered even when fading was considered. Considering the fact that bones are not directly exposed to light (protected by the skin and the flesh) or to high temperatures, it seems that they could be used at retrospective dosimetry and the identification of irradiated food products containing bone (food post-sterilization dosimetry).
1. Introduction Release of radiation in the environment can take place during acci dents or leakages due to human error or equipment failure (e.g. Pradhan et al., 2012). Despite all precautionary measures taken, nuclear power plants always have the risk of the inadvertently release of radiation in low or extremely high doses, with the most representative examples those of the Chernobyl Nuclear Power Plant Disaster in Ukraine in 1986 and the recent Fukushima Daiichi Nuclear Disaster, in Japan in 2011. In addition, the use of nuclear weapons or their implementation in terrorist events increase the possibility of a radiation related incident. For this purpose, estimation of the radiation dose as early as possible is imperative in order measures for the protection of population and human health to be taken (Mrozik et al., 2014). This is the research object of retrospective dosimetry, which seeks for materials that can be used as probes for the dose assessment by means of several methods, such as Electron Paramagnetic Resonance, Thermoluminescence, Opti cally Stimulated Luminescence etc. Numerous materials used in daily life have been studied up to
present towards this direction using the above methods (e.g. Mesterhazy et al., 2012; Wieser et al., 1994). However, few are the studies which investigate the potential use of biological materials as dosimeters for retrospective dosimetry. Such examples constitute tooth enamel (e.g. Meriç et al., 2015; Romanyukha et al., 2014) and fingernails (e.g. Sahiner et al., 2015; Trompier et al., 2007). However, all of the relative studies focus on human biological materials. Future studies should seek for non-human biological materials, which can be found in nature in abundance or in/on other living or ganisms, which will also be exposed to radiation in case of an accident. Towards this direction, in a recent study (Kazakis et al., 2016) the possibility of using insects, and specifically their wings, as retrospective dosimeters was investigated by means of OSL with encouraging results. To the same respect, the present work explores the luminescence behavior of animal bones and more specifically, chicken bones, using OSL in order to examine whether they can be used for the dose assess ment. Animal bones’ composition is similar to that of human and they could be a good substitute, since death and/or amputation is required in order to be able to measure human bones in the case of an accident (e.g.
* Corresponding author. E-mail addresses: [email protected], [email protected] (N.A. Kazakis), [email protected] (N.C. Tsirliganis). https://doi.org/10.1016/j.apradiso.2019.108899 Received 18 July 2019; Received in revised form 3 September 2019; Accepted 19 September 2019 Available online 20 September 2019 0969-8043/© 2019 Elsevier Ltd. All rights reserved.
N.A. Kazakis and N.C. Tsirliganis
Applied Radiation and Isotopes 154 (2019) 108899
Desrosiers, 1993; Breen and Battista, 1995). The inorganic component of bones, as of the tooth enamel as well, is mainly hydroxyapatite (crystalline calcium phosphate), which has been studied as material individually (e.g. Polymeris et al., 2011; Roman- Lopez et al., 2014; Zarate-Medina et al., 2015). Few researchers have studied the luminescence behavior of human bones after their death or amputation (e.g. Breen and Battista, 1995), while more studies were also accomplished mainly for dating purposes using human remains (e.g. Driver, 1979; Meric et al., 2008). To the authors’ best knowledge, studies on natural animal bones are handful and target at using the inorganic hydroxyapatite of the bones of animal remains for dating evaluation (e.g. Roman-Lopez et al., 2014) with discouraging results. In addition, the results of the present work can also contribute to wards the use of animal bones as dosimeters at the post-sterilization dosimetry of foods. Sterilization by means of gamma irradiation gains ground the last decades in the food industry, since it permits the fast and heat-free sterilization of heat-sensitive foodstuffs (Sulaxana Kumari Chauhan et al., 2009). Since exposure of foods to ionizing radiation may lead to their degradation, putting in jeopardy the health of the con sumer, there is a need to establish a method to identify irradiated foods (post-sterilization dosimetry) for regulatory compliance purposes. Few are the previous studies that explored the possibility of identi fying irradiated meat (among them chicken) by measuring the bones individually, but most of them used ESR (e.g. Desrosiers and Simic, 1988; Delinc�ee, 1993; Chawla and Thomas, 2004) or gas chromatog raphy (e.g. Morehouse et al., 1991; Morehouse and Ku, 1993). Works with thermoluminescence to the same direction are only handful (e.g. Oduko and Spyrou, 1990; Atta et al., 2001). Oduko and Spyrou (1990) were of the first who used Thermoluminescence to study bone samples from foodstuffs, but their work was not so detailed and limited to tem peratures up to 300 οC due to their heat-sensitivity. However, they observed that the method can be used to distinguish irradiated from unirradiated bone even after 8 weeks post the radiation exposure. To the Author’s best knowledge, there is not a recent similar work investigating the dosimetric properties of bones employing luminescence techniques and especially OSL. According to the above, the scope of the present study is to investi gate the luminescence behavior of chicken bones by means of OSL in order to explore their potential use as accidental/retrospective/forensic and/or food post-sterilization dosimeters.
2.2. Instruments and methods In all cases the mass of the measured sample was about 8.0 mg. All continuous-wave OSL measurements were conducted using a Riso TL/ OSL reader (model TL/OSL-DA-15). A 9235QA photomultiplier tube with the appropriate filter, namely a Hoya U-340 with maximum transmittance at approximately 340 nm and full width at half maximum (FWHM) about 80 nm, was used for light detection. All sample carriers (stainless steel cups) used in the study were first cleaned with the method suggested by Kazakis et al. (2015) and then measured empty at a beta-dose of 100 Gy to ensure that no contaminant signal is recorded. In the present study, doses from 0.05 up to 8.5 kGy were applied, which is comparable to that used during the sterilization process with ionizing radiation. 3. Results and discussion 3.1. CW-OSL features Fig. 1 presents a typical CW-OSL decay curve recorded immediately after exposure to 3.0 kGy for a chicken-bone sample. An initial quickly decaying part in the first 4–5 s of stimulation is observed. The curve then smoothly decays and reaches the background level in relatively short time (less than 100 s), indicating the involvement of fast and probably easy-to-bleach components. 3.2. Sensitization of OSL decay curve In order to investigate the potential sensitization of the OSL decay curve a single aliquot was subjected to ten consecutive cycles of irra diation and subsequent OSL measurement, after the zero-dose response was acquired: Step 1: Step 2: Step 3: Step 4:
OSL for 400 s (zero-dose response) Irradiation with test dose (150 Gy or 750 Gy) OSL for 400 s Repeat Steps 2 and 3 for nine more times
Sensitization was investigated on two different aliquots for two different doses (150 Gy and 750 Gy). Results are depicted in Fig. 2.
2. Experimental procedure 2.1. Sample preparation Several fresh chicken legs were procured by a butcher shop and the flesh and skin were removed in the laboratory using a scalpel in order to isolate the bone of each leg. The bones were then washed with distilled water in a supersonic bath to remove any contamination. Then the legs were gently broken in the middle so as the internal part of the bone, and specifically the bone marrow, to become exposed. Using a thin stainless steel wire an effort was made to create paths inside the bone marrow and to remove most of it. The above is crucial for the next cleaning/prepa ration stage. The bones were then placed in beakers and were washed several times with hydrogen peroxide (H2O2 3%) in a supersonic bath until no foam and/or contamination was observed on the solution’s surface. Then they were left inside the H2O2 solution overnight (~16 h). With this procedure the bone marrow was completely removed in addition to the collagen, the organic part of the bones. The clean bones were then dried in an oven at 50 � C. Finally, the dried bones were gently ground in an agate mortar to produce small particles. The latter were further sieved and bone grains of size 75–150 μm were selected for the measurements. Fig. 1. Typical OSL decay curves for chicken bone; dose 3.0 kGy. 2
N.A. Kazakis and N.C. Tsirliganis
Applied Radiation and Isotopes 154 (2019) 108899
Fig. 3. Dose response study; the inset shows the linear behavior of the lower dose range; integration time for response calculation is 1 s.
Fig. 2. Sensitization study for test dose of 150 Gy and 750 Gy.
Based on this study, it was found that a detectable signal was acquired for doses >50 Gy. The above limit is not low enough to allow the use of bones as emergency dosimeters. In such cases, doses as low as a fraction of a gray have to be determined. However, chicken or animal bones in general could possibly be used for the estimation of doses in case of nuclear accidents and/or for retrospective/forensic purposes, where higher doses are involved. The same is also supported by Zdravkova et al. (2004), who calculated a minimum detectable dose of ~60 Gy conducting in vivo EPR measurements on a human finger.
Integration time was the first 1.5 s and 4 s of stimulation for the dose of 150 Gy and 750 Gy respectively. It must be noted that all data were normalized with respect to the data of the first cycle and that in all cases the respective background signal was subtracted from the original signal. Sensitization is independent of the dose applied, since behavior is similar for both doses (150 Gy and 750 Gy). The response increases rapidly for up to 50% in the first two consecutive cycles and then re mains practically stable for the next irradiation/stimulation cycles. That would probably mean that the population of the competitors (i.e., deep traps) is not large and they approach saturation after the first 2–3 irra diations. Thus, in the next cycles the same shallow traps, which are more susceptible to the light stimulation are filled and emptied over and over in every irradiation/stimulation cycle, leading to a practically negligible change in the normalized OSL response.
3.4. Fading of the signal with storage in dark The fading of the OSL signal was studied for various time periods (from 24 h up to 2 months). A dose of 1.5 kGy was administered to a number of aliquots and the OSL was measured immediately after the irradiation. Then a similar dose of 1.5 kGy was administered to the ali quots and they were subsequently stored in dark in room temperature (~20 � C) for various time periods. At the end of each time period the aliquot was stimulated with blue light and the remaining OSL signal was recorded. The OSL response was calculated and normalized with the one acquired immediately after the initial irradiation. Fading results are presented in Fig. 4 for the various time durations. Bone loses almost half of its initial signal during the first week. Over the next days, fading of the signal seems negligible. Although strong fading of the OSL signal is evident, yet, an appreciable signal remains stored in the bones and could be used for the detection of irradiated chicken (or poultry) and/or the estimation of the sterilization and/or accidental dose. In addition, the experimental normalized OSL decay data of the fading study can be explained best by a second-order kinetic decay function:
3.3. OSL dose response and lower detection limit A dose response study also took place for a wide range of doses (0.05–6 kGy) and the results are illustrated in Fig. 3. OSL response in creases with a relatively high rate for doses up to ~2 kGy. For higher doses, the response still increases, but with lower rate until saturation takes place (dose>5–6 kGy). It should be noted that in the USA the recommended gamma-dose for sterilization of poultry is between 1.5 and 3.0 kGy (e.g. Pelicia et al., 2015; Sulaxana Kumari Chauhan et al., 2009). Thus, the above results of the dose response are promising for the use of bones in the post-sterilization dosimetry of chicken, poultry or other bone-containing food products in general. It is obvious that the OSL response of the bone displays a perfect linear response in the range 0.05–1 kGy, while response over the entire dose range can be fitted with an exponential saturation curve of the form I ¼ m1 ⋅½1 e D=m2 �, where I is the OSL response, D the dose and m1 and m2 are constants. The lower limit of detection was also calculated and it was consid ered as three times the standard deviation of the background signal (zero dose reading). According to the above, it was found that the lower limit of detection is ~18 Gy. To validate the above, the dose response was also studied in a narrow range (10–100 Gy) using a small increment (10 Gy).
If ¼ I∞ þ
I ’o ’ I o ⋅kd ⋅tstor
þ1
(1)
where (I∞ þI’o Þ; If and I∞ represent the normalized response at zero (tstor ¼ 0), any time and at infinite respectively, while kd and tstor repre sent the decay constant and the storage time respectively. In the case of the chicken bones, it was found that I∞ ¼ 0:49; I’o ¼ 0.50 and kd ¼ 1.23 days 1. Obviously, the fading factor for any storage time post-irradiation can 3
N.A. Kazakis and N.C. Tsirliganis
Applied Radiation and Isotopes 154 (2019) 108899
3.5.1. Dose recovery test with the SARHS protocol neglecting fading after exposure to radiation A first dose recovery test was conducted without considering fading after exposure to radiation. Thus, a chicken-bone sample was irradiated with the unknown sterilization dose of 2.2 kGy and the corresponding OSL decay curve was acquired directly. Then the steps of the SARHS protocol were followed to construct the calibration curve (see Fig. 3 in Kazakis et al., 2017). Fig. 5a illustrates the calibration data and the fitted curve used for the calculation of the “unknown” sterilization and test dose, while Table 1 presents the results of the recovery test. The calibration data were perfectly fitted with an exponential satu ration curve (as previously discussed). In addition, the SARHS protocol can be used for the correct calculation of the sterilization dose with a small error (difference between the calculated and the actual dose) in the case of heat-sensitive chicken bones. In the same respect, the test dose was also determined with minor error. 3.5.2. Dose recovery test with the SARHS protocol considering fading after exposure to radiation A dose recovery test was also conducted taking into account fading of the OSL signal after exposure to radiation. For this purpose, a different chicken-bone sample was irradiated with the sterilization dose of Fig. 4. Fading of the normalized OSL response for the bone and its fitting (solid line) with Eq. (1).
be calculated directly using Eq. (1) and the calculated values. The time of irradiation can be estimated by the LOT number which is written on the package of the product(s) and provides information about the “his tory” of the production. 3.5. Dose recovery test All the above luminescence features of the chicken bones are promising indicating that irradiated poultry or other animals could be identified using OSL. In order to investigate whether the sterilization/ accidental dose is also possible to be determined, a dose recovery test was also conducted using the SARHS protocol (Kazakis et al., 2017). The SARHS protocol is a single aliquot regenerative-dose protocol suitable for heat-sensitive materials exhibiting sensitization for the estimation of the equivalent dose by means of OSL. The protocol elim inates any sensitization effects without encompassing any heating of the sample. In short, the SARHS protocol introduces an optical bleaching procedure under a solar simulator between the repeated irradiation/ stimulation cycles during the construction of the calibration curve, ensuring that all traps are completely emptied and the sample is restored to its initial state each time, e.g. before its exposure to radiation. Based on the above, chicken samples were first irradiated with an “unknown” sterilization dose (few kGy) and then the SARHS protocol was followed (for details see Fig. 3 in Kazakis et al., 2017). The optimum bleaching time is determined for the highest (maximum) laboratory dose to be used for the construction of the calibration curve (8.5 kGy in the present case). That would assure that the determined bleaching time is adequate to restore the sample to its initial state after its bleaching be tween the repeated irradiation/stimulation cycles for lower doses as well. Three different values of bleaching time were tested (30, 60 and 90 min). It was found that the optimum bleaching time is 60 min. Be sides the sterilization dose, after the construction of the calibration curve and the end of the protocol, a lower test dose was also applied (which was not taken into account in the calibration curve) in order to investigate any potential degradation of the bones. The sterilization and test dose selected were 2.2 kGy (e.g. Pelicia et al., 2015; Sulaxana Kumari Chauhan et al., 2009) and 0.6 kGy respectively.
Fig. 5. Dose recovery test using the SARHS protocol for chicken bone: (a) neglecting fading, (b) considering fading 24 h after exposure to radiation; integration time for response calculation is 3 s; the thick line corresponds to the fitted calibration curve. 4
N.A. Kazakis and N.C. Tsirliganis
Applied Radiation and Isotopes 154 (2019) 108899
Table 1 Determination of the sterilization and test dose (dose recovery test) using the SARHS protocol for chicken-bone samples; functions of the corresponding calibration curves are presented in Fig. 5. Fading
“Sterilization” dose (Gy)
Recovered dose (Gy)
Difference (%)
Test dose (Gy)
Recovered dose (Gy)
Difference (%)
No 24 h
2198.8 2198.8
2229.4 1987.1
1.39 9.63
599.2 599.2
511.3 540.8
14.67 9.74
2.2 kGy. However, the corresponding OSL readout took place 24 h after the exposure to radiation, during which the aliquot was kept in dark. As a result, an underestimated value of the real “sterilization” dose was calculated due to fading. This value was then used as a test dose for the determination of the fading factor as dictated by the SARHS (see Fig. 4 in Kazakis et al., 2017). Finally, the value was corrected using the esti mated fading factor. The calibration data and the “unknown” doses are presented in Fig. 5b, while results of the dose recovery test considering the fading of the OSL signal 24 h after the exposure to radiation are presented in Table 1. It is evident that the SARHS protocol can again calculate correctly the fading factor and the sterilization/test doses in the case of the chicken bones within an acceptable error.
References Atta, S., Sattar, A., Ahmad, A., Ali, I., Nagra, S.A., Ahmad, T., 2001. Suitability of thermoluminescence for the detection of irradiated chicken and fish. J. Radioanal. Nucl. Chem. 250 (3), 537–540. Breen, S.L., Battista, J.J., 1995. Radiation dosimetry in human bone using electron paramagnetic resonance. Phys. Med. Biol. 40, 2065–2077. Chauhan, Sulaxana Kumari, Kumar, R., Nadanasabapathy, S., Bawa, A.S., 2009. Detection methods for irradiated foods. Compr. Rev. Food Sci. Food Saf. 8, 4–16. Chawla, S.P., Thomas, P., 2004. Identification of irradiated meat using electron spin resonance spectroscopy: results of blind trials. Int. J. Food Sci. Technol. 39, 653–660. Delinc� ee, H., 1993. Control of irradiated food: recent developments in analytical detection methods. Radiat. Phys. Chem. 42 (1–3), 351–357. Desrosiers, M.F., 1993. EPR bone dosimetry: a new approach to spectral deconvolution problems. Appl. Radiat. Isot. 44 (1–2), 81–83. Desrosiers, M.F., Simic, M.G., 1988. Post-irradiation dosimetry of meat by electron spin resonance spectroscopy of bones. J. Agric. Food Chem. 36, 601–603. Driver, H.S.T., 1979. The preparation of thin slices of bone and shell for thermoluminescence. PACT 3, 290–297. Kazakis, N.A., Kitis, G., Tsirliganis, N.C., 2015. A cleaning method to minimize contaminant luminescence signal of empty sample carriers using off-the-shelf chemical agents. Appl. Radiat. Isot. 95, 226–232. Kazakis, N.A., Tsetine, Anastasia Th, Kitis, G., Tsirliganis, N.C., 2016. Insect wings as accidental/retrospective dosimeters: an optically stimulated luminescence investigation. Radiat. Meas. 89, 74–81. Kazakis, N.A., Tsetine, A.Th, Kitis, G., Tsirliganis, N.C., 2017. A SAR protocol for heatsensitive materials exhibiting sensitization (SARHS) for the estimation of the equivalent dose. Radiat. Meas. 99, 1–9. Meric, N., Kos¸al, M., Atlıhan, M.A., Yüce, Ü.R., 2008. OSL properties of anthropological bone and tooth. Radiat. Phys. Chem. 77, 685–689. Meriç, N., Yuce, U.R., Sahiner, E., Damianidis, A., Polymeris, G.S., 2015. Dose response and fading studies on de-proteinated tooth enamel after de-convolution using the sum of general order kinetics and a component for tunnelling recombination. Radiat. Meas. 26, 297–305. Mesterhazy, D., Osvay, M., Kovacs, A., Kelemen, A., 2012. Accidental and retrospective dosimetry using TL method. Radiat. Phys. Chem. 8, 1525–1527. Morehouse, K.M., Ku, Y., 1993. Identification of irradiated foods by monitoring radiolytically produced hydrocarbons. Radiat. Phys. Chem. 42 (1–3), 359–362. Morehouse, K.M., Ku, Y., Albrecht, H.L., Yang, G.C., 1991. Gas chromatographic and electron spin resonance investigations of gamma-irradiated frog legs. Radiat. Phys. Chem. 38, 61–68. Mrozik, A., Marczewska, B., Bilski, P., Gieszczyk, W., 2014. Investigation of OSL signal of resistors from mobile phones for accidental dosimetry. Radiat. Meas. 71, 466–470. Oduko, J.M., Spyrou, N.M., 1990. Thermoluminescence of irradiated foodstuffs. Int. J. Radiat. Appl. Instrum. C Radiat. Phys. Chem. 36 (5), 603–607. Pelicia, K., Garcia, E.A., Molino, A.B., Santos, G.C., Vieira Filho, J.A., Santos, T.A., Berto, D.A., 2015. Chicken meat submitted to gamma radiation and packed with or without oxygen. Brazilian Journal of Poultry Science 17 (2), 255–262. Polymeris, G.S., Goudouri, O.M., Kontonasaki, E., Paraskevopoulos, K.M., Tsirliganis, N. C., Kitis, G., 2011. Thermoluminescence as a probe in bioactivity studies; the case of 58S sol-gel bioactive glass. J. Phys. D Appl. Phys. 44 (39), 1–8. Pradhan, A.S., Kim, J.L., Lee, J.I., 2012. Use of ubiquitous materials for the estimation of accidental exposures. J. Med. Phys. 37 (3), 121–123. Roman-Lopez, J., Correcher, V., Garcia-Guinea, J., Rivera, T., Lozano, I.B., 2014. Thermal and electron stimulated luminescence of natural bones, commercial hydroxyapatite and collagen. Spectrochim. Acta A Mol. Biomol. Spectrosc. 120, 610–615. Romanyukha, A., Trompier, F., Reyes, R.A., Christensen, D.M., Iddins, C.J., Sugarman, S. L., 2014. Electron paramagnetic resonance radiation dose assessment in fingernails of the victim exposed to high dose as result of an accident. Radiat. Environ. Biophys. 53 (4), 755–762. Sahiner, E., Meriç, N., Polymeris, G.S., 2015. Impact of different mechanical pretreatment to the EPR signals of human fingernails towards studying dose response and fading subjected to UV exposure or beta irradiation. Radiat. Meas. 82, 40–46. Trompier, F., Kornak, L., Calas, C., Romanyukha, A., Leblanc, B., Mitchell, C.A., Swartz, H., Clairand, I., 2007. Protocol for emergency EPR dosimetry in fingernails. Radiat. Meas. 42, 1085–1088.
4. Conclusions Chicken bones were investigated with optically stimulated lumi nescence in order to identify their potential luminescent properties which would allow their use as dosimeters in accidental/retrospective/ forensic and/or food post-sterilization dosimetry. In general the OSL sensitivity is low. In addition, bones exhibit sensitization in the first two consecutive cycles up to 50% which remains practically stable for the next irradiation/stimulation cycles. In any case optical bleaching of the sample for 60 min under the light of a solar simulator is capable to empty all traps and restore the sample to its initial state (before any irradiation). Results indicate that the OSL dose response is linear for doses up to ~1.0 kGy, while response over the entire dose range up to several kGy can be fitted with an exponential saturation curve. The lower limit of detection has been found equal to ~18 Gy which is quite high in order to use chicken bones as emergency dosimeter. Loss of the OSL signal is about 50% seven days after irradiation, when samples are kept in dark (fading). The remained stored signal remains stable for longer time periods up to two months post-irradiation in dark conditions. This is important, since bones are not directly exposed to light (protected by the skin and flesh) or to high tempera tures, thus they could be used at post-sterilization and retrospective dosimetry. Moreover, the fading behavior could be fitted using a secondorder kinetic decay function. A dose recovery test was also conducted using the SARHS protocol in order to investigate if the protocol is capable of calculating the sterili zation/accidental dose of irradiated chicken/poultry. The “sterilization” doses were recovered with small errors, thus further validating the protocol. The findings are very promising towards the use of bones in order to identify irradiated food containing bones and/or the use of chicken bones as accidental dosimeters, while the SARHS protocol can be applied for the correct estimation of the sterilization/accidental dose. Acknowledgement The present work was supported by the project "Computational Science and Technologies: Data, Content and Interaction"/"Technolo gies for Content Analysis in Culture", MIS code 5002437, co-financed by Greece (General Secretariat for Research & Technology) and European Union in the framework of the Operational Programme "Competitive ness, Entrepreneurship and Innovation" 2014-2020.
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Wieser, A., Goksu, H.Y., Regulla, D.F., Vogenauer, A., 1994. Limits of retrospective accident dosimetry by EPR and TL with natural materials. Radiat. Meas. 23 (2–3), 509–514. Zarate-Medina, J., Sandoval-Cede~ no, K.J., Barrera-Villatoro, A., Lemus-Ruiz, J., RiveraMontalvo, T., 2015. Thermal effect on thermoluminescence response of hydroxyapatite. Appl. Radiat. Isot. 100, 50–54.
Zdravkova, M., Crokart, N., Trompier, F., Beghein, N., Gallez, B., Debuyst, R., 2004. Non invasive determination of the irradiation dose in fingers using low frequency EPR. Phys. Med. Biol. 49, 2891–2898.
6
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: http://www.elsevier.com/locate/apradiso
Optically stimulated luminescence investigation of chicken bones towards their use at food post-sterilization and retrospective dosimetry Nikolaos A. Kazakis *, Nestor C. Tsirliganis Laboratory of Archaeometry and Physicochemical Measurements, R.C. ‘Athena’, P.O. Box 159, Kimmeria University Campus, 67100, Xanthi, Greece
A R T I C L E I N F O
A B S T R A C T
Keywords: Chicken Bones Hydroxyapatite Retrospective dosimetry Post-sterilization dosimetry Optically stimulated luminescence
The present work explores the luminescence behavior of animal bones and more specifically, chicken bones, using OSL in order to investigate whether they can be used for the dose assessment in the case of an accident or as dosimeters at the post-sterilization dosimetry of foods. Results indicate that the OSL sensitivity is rather low and the lower detection limit is ~18 Gy eliminating the possibility of using bones as emergency dosimeter. However, the OSL dose response is linear for doses up to ~1.0 kGy, while response over the entire dose range, up to several kGy, can be fitted with an exponential saturation curve. When bones are kept in dark, half of the initial OSL signal is lost seven days after irradiation, with no further loss for longer time periods up to two months post-irradiation. Since bones are heat-sensitive and exhibit sensitization, a dose recovery test was also conducted using the SARHS protocol in order to investigate if the protocol is capable of calculating the sterilization/accidental dose of irradiated chicken/poultry. The “unknown” doses were successfully recovered even when fading was considered. Considering the fact that bones are not directly exposed to light (protected by the skin and the flesh) or to high temperatures, it seems that they could be used at retrospective dosimetry and the identification of irradiated food products containing bone (food post-sterilization dosimetry).
1. Introduction Release of radiation in the environment can take place during acci dents or leakages due to human error or equipment failure (e.g. Pradhan et al., 2012). Despite all precautionary measures taken, nuclear power plants always have the risk of the inadvertently release of radiation in low or extremely high doses, with the most representative examples those of the Chernobyl Nuclear Power Plant Disaster in Ukraine in 1986 and the recent Fukushima Daiichi Nuclear Disaster, in Japan in 2011. In addition, the use of nuclear weapons or their implementation in terrorist events increase the possibility of a radiation related incident. For this purpose, estimation of the radiation dose as early as possible is imperative in order measures for the protection of population and human health to be taken (Mrozik et al., 2014). This is the research object of retrospective dosimetry, which seeks for materials that can be used as probes for the dose assessment by means of several methods, such as Electron Paramagnetic Resonance, Thermoluminescence, Opti cally Stimulated Luminescence etc. Numerous materials used in daily life have been studied up to
present towards this direction using the above methods (e.g. Mesterhazy et al., 2012; Wieser et al., 1994). However, few are the studies which investigate the potential use of biological materials as dosimeters for retrospective dosimetry. Such examples constitute tooth enamel (e.g. Meriç et al., 2015; Romanyukha et al., 2014) and fingernails (e.g. Sahiner et al., 2015; Trompier et al., 2007). However, all of the relative studies focus on human biological materials. Future studies should seek for non-human biological materials, which can be found in nature in abundance or in/on other living or ganisms, which will also be exposed to radiation in case of an accident. Towards this direction, in a recent study (Kazakis et al., 2016) the possibility of using insects, and specifically their wings, as retrospective dosimeters was investigated by means of OSL with encouraging results. To the same respect, the present work explores the luminescence behavior of animal bones and more specifically, chicken bones, using OSL in order to examine whether they can be used for the dose assess ment. Animal bones’ composition is similar to that of human and they could be a good substitute, since death and/or amputation is required in order to be able to measure human bones in the case of an accident (e.g.
* Corresponding author. E-mail addresses: [email protected], [email protected] (N.A. Kazakis), [email protected] (N.C. Tsirliganis). https://doi.org/10.1016/j.apradiso.2019.108899 Received 18 July 2019; Received in revised form 3 September 2019; Accepted 19 September 2019 Available online 20 September 2019 0969-8043/© 2019 Elsevier Ltd. All rights reserved.
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Desrosiers, 1993; Breen and Battista, 1995). The inorganic component of bones, as of the tooth enamel as well, is mainly hydroxyapatite (crystalline calcium phosphate), which has been studied as material individually (e.g. Polymeris et al., 2011; Roman- Lopez et al., 2014; Zarate-Medina et al., 2015). Few researchers have studied the luminescence behavior of human bones after their death or amputation (e.g. Breen and Battista, 1995), while more studies were also accomplished mainly for dating purposes using human remains (e.g. Driver, 1979; Meric et al., 2008). To the authors’ best knowledge, studies on natural animal bones are handful and target at using the inorganic hydroxyapatite of the bones of animal remains for dating evaluation (e.g. Roman-Lopez et al., 2014) with discouraging results. In addition, the results of the present work can also contribute to wards the use of animal bones as dosimeters at the post-sterilization dosimetry of foods. Sterilization by means of gamma irradiation gains ground the last decades in the food industry, since it permits the fast and heat-free sterilization of heat-sensitive foodstuffs (Sulaxana Kumari Chauhan et al., 2009). Since exposure of foods to ionizing radiation may lead to their degradation, putting in jeopardy the health of the con sumer, there is a need to establish a method to identify irradiated foods (post-sterilization dosimetry) for regulatory compliance purposes. Few are the previous studies that explored the possibility of identi fying irradiated meat (among them chicken) by measuring the bones individually, but most of them used ESR (e.g. Desrosiers and Simic, 1988; Delinc�ee, 1993; Chawla and Thomas, 2004) or gas chromatog raphy (e.g. Morehouse et al., 1991; Morehouse and Ku, 1993). Works with thermoluminescence to the same direction are only handful (e.g. Oduko and Spyrou, 1990; Atta et al., 2001). Oduko and Spyrou (1990) were of the first who used Thermoluminescence to study bone samples from foodstuffs, but their work was not so detailed and limited to tem peratures up to 300 οC due to their heat-sensitivity. However, they observed that the method can be used to distinguish irradiated from unirradiated bone even after 8 weeks post the radiation exposure. To the Author’s best knowledge, there is not a recent similar work investigating the dosimetric properties of bones employing luminescence techniques and especially OSL. According to the above, the scope of the present study is to investi gate the luminescence behavior of chicken bones by means of OSL in order to explore their potential use as accidental/retrospective/forensic and/or food post-sterilization dosimeters.
2.2. Instruments and methods In all cases the mass of the measured sample was about 8.0 mg. All continuous-wave OSL measurements were conducted using a Riso TL/ OSL reader (model TL/OSL-DA-15). A 9235QA photomultiplier tube with the appropriate filter, namely a Hoya U-340 with maximum transmittance at approximately 340 nm and full width at half maximum (FWHM) about 80 nm, was used for light detection. All sample carriers (stainless steel cups) used in the study were first cleaned with the method suggested by Kazakis et al. (2015) and then measured empty at a beta-dose of 100 Gy to ensure that no contaminant signal is recorded. In the present study, doses from 0.05 up to 8.5 kGy were applied, which is comparable to that used during the sterilization process with ionizing radiation. 3. Results and discussion 3.1. CW-OSL features Fig. 1 presents a typical CW-OSL decay curve recorded immediately after exposure to 3.0 kGy for a chicken-bone sample. An initial quickly decaying part in the first 4–5 s of stimulation is observed. The curve then smoothly decays and reaches the background level in relatively short time (less than 100 s), indicating the involvement of fast and probably easy-to-bleach components. 3.2. Sensitization of OSL decay curve In order to investigate the potential sensitization of the OSL decay curve a single aliquot was subjected to ten consecutive cycles of irra diation and subsequent OSL measurement, after the zero-dose response was acquired: Step 1: Step 2: Step 3: Step 4:
OSL for 400 s (zero-dose response) Irradiation with test dose (150 Gy or 750 Gy) OSL for 400 s Repeat Steps 2 and 3 for nine more times
Sensitization was investigated on two different aliquots for two different doses (150 Gy and 750 Gy). Results are depicted in Fig. 2.
2. Experimental procedure 2.1. Sample preparation Several fresh chicken legs were procured by a butcher shop and the flesh and skin were removed in the laboratory using a scalpel in order to isolate the bone of each leg. The bones were then washed with distilled water in a supersonic bath to remove any contamination. Then the legs were gently broken in the middle so as the internal part of the bone, and specifically the bone marrow, to become exposed. Using a thin stainless steel wire an effort was made to create paths inside the bone marrow and to remove most of it. The above is crucial for the next cleaning/prepa ration stage. The bones were then placed in beakers and were washed several times with hydrogen peroxide (H2O2 3%) in a supersonic bath until no foam and/or contamination was observed on the solution’s surface. Then they were left inside the H2O2 solution overnight (~16 h). With this procedure the bone marrow was completely removed in addition to the collagen, the organic part of the bones. The clean bones were then dried in an oven at 50 � C. Finally, the dried bones were gently ground in an agate mortar to produce small particles. The latter were further sieved and bone grains of size 75–150 μm were selected for the measurements. Fig. 1. Typical OSL decay curves for chicken bone; dose 3.0 kGy. 2
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Applied Radiation and Isotopes 154 (2019) 108899
Fig. 3. Dose response study; the inset shows the linear behavior of the lower dose range; integration time for response calculation is 1 s.
Fig. 2. Sensitization study for test dose of 150 Gy and 750 Gy.
Based on this study, it was found that a detectable signal was acquired for doses >50 Gy. The above limit is not low enough to allow the use of bones as emergency dosimeters. In such cases, doses as low as a fraction of a gray have to be determined. However, chicken or animal bones in general could possibly be used for the estimation of doses in case of nuclear accidents and/or for retrospective/forensic purposes, where higher doses are involved. The same is also supported by Zdravkova et al. (2004), who calculated a minimum detectable dose of ~60 Gy conducting in vivo EPR measurements on a human finger.
Integration time was the first 1.5 s and 4 s of stimulation for the dose of 150 Gy and 750 Gy respectively. It must be noted that all data were normalized with respect to the data of the first cycle and that in all cases the respective background signal was subtracted from the original signal. Sensitization is independent of the dose applied, since behavior is similar for both doses (150 Gy and 750 Gy). The response increases rapidly for up to 50% in the first two consecutive cycles and then re mains practically stable for the next irradiation/stimulation cycles. That would probably mean that the population of the competitors (i.e., deep traps) is not large and they approach saturation after the first 2–3 irra diations. Thus, in the next cycles the same shallow traps, which are more susceptible to the light stimulation are filled and emptied over and over in every irradiation/stimulation cycle, leading to a practically negligible change in the normalized OSL response.
3.4. Fading of the signal with storage in dark The fading of the OSL signal was studied for various time periods (from 24 h up to 2 months). A dose of 1.5 kGy was administered to a number of aliquots and the OSL was measured immediately after the irradiation. Then a similar dose of 1.5 kGy was administered to the ali quots and they were subsequently stored in dark in room temperature (~20 � C) for various time periods. At the end of each time period the aliquot was stimulated with blue light and the remaining OSL signal was recorded. The OSL response was calculated and normalized with the one acquired immediately after the initial irradiation. Fading results are presented in Fig. 4 for the various time durations. Bone loses almost half of its initial signal during the first week. Over the next days, fading of the signal seems negligible. Although strong fading of the OSL signal is evident, yet, an appreciable signal remains stored in the bones and could be used for the detection of irradiated chicken (or poultry) and/or the estimation of the sterilization and/or accidental dose. In addition, the experimental normalized OSL decay data of the fading study can be explained best by a second-order kinetic decay function:
3.3. OSL dose response and lower detection limit A dose response study also took place for a wide range of doses (0.05–6 kGy) and the results are illustrated in Fig. 3. OSL response in creases with a relatively high rate for doses up to ~2 kGy. For higher doses, the response still increases, but with lower rate until saturation takes place (dose>5–6 kGy). It should be noted that in the USA the recommended gamma-dose for sterilization of poultry is between 1.5 and 3.0 kGy (e.g. Pelicia et al., 2015; Sulaxana Kumari Chauhan et al., 2009). Thus, the above results of the dose response are promising for the use of bones in the post-sterilization dosimetry of chicken, poultry or other bone-containing food products in general. It is obvious that the OSL response of the bone displays a perfect linear response in the range 0.05–1 kGy, while response over the entire dose range can be fitted with an exponential saturation curve of the form I ¼ m1 ⋅½1 e D=m2 �, where I is the OSL response, D the dose and m1 and m2 are constants. The lower limit of detection was also calculated and it was consid ered as three times the standard deviation of the background signal (zero dose reading). According to the above, it was found that the lower limit of detection is ~18 Gy. To validate the above, the dose response was also studied in a narrow range (10–100 Gy) using a small increment (10 Gy).
If ¼ I∞ þ
I ’o ’ I o ⋅kd ⋅tstor
þ1
(1)
where (I∞ þI’o Þ; If and I∞ represent the normalized response at zero (tstor ¼ 0), any time and at infinite respectively, while kd and tstor repre sent the decay constant and the storage time respectively. In the case of the chicken bones, it was found that I∞ ¼ 0:49; I’o ¼ 0.50 and kd ¼ 1.23 days 1. Obviously, the fading factor for any storage time post-irradiation can 3
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3.5.1. Dose recovery test with the SARHS protocol neglecting fading after exposure to radiation A first dose recovery test was conducted without considering fading after exposure to radiation. Thus, a chicken-bone sample was irradiated with the unknown sterilization dose of 2.2 kGy and the corresponding OSL decay curve was acquired directly. Then the steps of the SARHS protocol were followed to construct the calibration curve (see Fig. 3 in Kazakis et al., 2017). Fig. 5a illustrates the calibration data and the fitted curve used for the calculation of the “unknown” sterilization and test dose, while Table 1 presents the results of the recovery test. The calibration data were perfectly fitted with an exponential satu ration curve (as previously discussed). In addition, the SARHS protocol can be used for the correct calculation of the sterilization dose with a small error (difference between the calculated and the actual dose) in the case of heat-sensitive chicken bones. In the same respect, the test dose was also determined with minor error. 3.5.2. Dose recovery test with the SARHS protocol considering fading after exposure to radiation A dose recovery test was also conducted taking into account fading of the OSL signal after exposure to radiation. For this purpose, a different chicken-bone sample was irradiated with the sterilization dose of Fig. 4. Fading of the normalized OSL response for the bone and its fitting (solid line) with Eq. (1).
be calculated directly using Eq. (1) and the calculated values. The time of irradiation can be estimated by the LOT number which is written on the package of the product(s) and provides information about the “his tory” of the production. 3.5. Dose recovery test All the above luminescence features of the chicken bones are promising indicating that irradiated poultry or other animals could be identified using OSL. In order to investigate whether the sterilization/ accidental dose is also possible to be determined, a dose recovery test was also conducted using the SARHS protocol (Kazakis et al., 2017). The SARHS protocol is a single aliquot regenerative-dose protocol suitable for heat-sensitive materials exhibiting sensitization for the estimation of the equivalent dose by means of OSL. The protocol elim inates any sensitization effects without encompassing any heating of the sample. In short, the SARHS protocol introduces an optical bleaching procedure under a solar simulator between the repeated irradiation/ stimulation cycles during the construction of the calibration curve, ensuring that all traps are completely emptied and the sample is restored to its initial state each time, e.g. before its exposure to radiation. Based on the above, chicken samples were first irradiated with an “unknown” sterilization dose (few kGy) and then the SARHS protocol was followed (for details see Fig. 3 in Kazakis et al., 2017). The optimum bleaching time is determined for the highest (maximum) laboratory dose to be used for the construction of the calibration curve (8.5 kGy in the present case). That would assure that the determined bleaching time is adequate to restore the sample to its initial state after its bleaching be tween the repeated irradiation/stimulation cycles for lower doses as well. Three different values of bleaching time were tested (30, 60 and 90 min). It was found that the optimum bleaching time is 60 min. Be sides the sterilization dose, after the construction of the calibration curve and the end of the protocol, a lower test dose was also applied (which was not taken into account in the calibration curve) in order to investigate any potential degradation of the bones. The sterilization and test dose selected were 2.2 kGy (e.g. Pelicia et al., 2015; Sulaxana Kumari Chauhan et al., 2009) and 0.6 kGy respectively.
Fig. 5. Dose recovery test using the SARHS protocol for chicken bone: (a) neglecting fading, (b) considering fading 24 h after exposure to radiation; integration time for response calculation is 3 s; the thick line corresponds to the fitted calibration curve. 4
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Table 1 Determination of the sterilization and test dose (dose recovery test) using the SARHS protocol for chicken-bone samples; functions of the corresponding calibration curves are presented in Fig. 5. Fading
“Sterilization” dose (Gy)
Recovered dose (Gy)
Difference (%)
Test dose (Gy)
Recovered dose (Gy)
Difference (%)
No 24 h
2198.8 2198.8
2229.4 1987.1
1.39 9.63
599.2 599.2
511.3 540.8
14.67 9.74
2.2 kGy. However, the corresponding OSL readout took place 24 h after the exposure to radiation, during which the aliquot was kept in dark. As a result, an underestimated value of the real “sterilization” dose was calculated due to fading. This value was then used as a test dose for the determination of the fading factor as dictated by the SARHS (see Fig. 4 in Kazakis et al., 2017). Finally, the value was corrected using the esti mated fading factor. The calibration data and the “unknown” doses are presented in Fig. 5b, while results of the dose recovery test considering the fading of the OSL signal 24 h after the exposure to radiation are presented in Table 1. It is evident that the SARHS protocol can again calculate correctly the fading factor and the sterilization/test doses in the case of the chicken bones within an acceptable error.
References Atta, S., Sattar, A., Ahmad, A., Ali, I., Nagra, S.A., Ahmad, T., 2001. Suitability of thermoluminescence for the detection of irradiated chicken and fish. J. Radioanal. Nucl. Chem. 250 (3), 537–540. Breen, S.L., Battista, J.J., 1995. Radiation dosimetry in human bone using electron paramagnetic resonance. Phys. Med. Biol. 40, 2065–2077. Chauhan, Sulaxana Kumari, Kumar, R., Nadanasabapathy, S., Bawa, A.S., 2009. Detection methods for irradiated foods. Compr. Rev. Food Sci. Food Saf. 8, 4–16. Chawla, S.P., Thomas, P., 2004. Identification of irradiated meat using electron spin resonance spectroscopy: results of blind trials. Int. J. Food Sci. Technol. 39, 653–660. Delinc� ee, H., 1993. Control of irradiated food: recent developments in analytical detection methods. Radiat. Phys. Chem. 42 (1–3), 351–357. Desrosiers, M.F., 1993. EPR bone dosimetry: a new approach to spectral deconvolution problems. Appl. Radiat. Isot. 44 (1–2), 81–83. Desrosiers, M.F., Simic, M.G., 1988. Post-irradiation dosimetry of meat by electron spin resonance spectroscopy of bones. J. Agric. Food Chem. 36, 601–603. Driver, H.S.T., 1979. The preparation of thin slices of bone and shell for thermoluminescence. PACT 3, 290–297. Kazakis, N.A., Kitis, G., Tsirliganis, N.C., 2015. A cleaning method to minimize contaminant luminescence signal of empty sample carriers using off-the-shelf chemical agents. Appl. Radiat. Isot. 95, 226–232. Kazakis, N.A., Tsetine, Anastasia Th, Kitis, G., Tsirliganis, N.C., 2016. Insect wings as accidental/retrospective dosimeters: an optically stimulated luminescence investigation. Radiat. Meas. 89, 74–81. Kazakis, N.A., Tsetine, A.Th, Kitis, G., Tsirliganis, N.C., 2017. A SAR protocol for heatsensitive materials exhibiting sensitization (SARHS) for the estimation of the equivalent dose. Radiat. Meas. 99, 1–9. Meric, N., Kos¸al, M., Atlıhan, M.A., Yüce, Ü.R., 2008. OSL properties of anthropological bone and tooth. Radiat. Phys. Chem. 77, 685–689. Meriç, N., Yuce, U.R., Sahiner, E., Damianidis, A., Polymeris, G.S., 2015. Dose response and fading studies on de-proteinated tooth enamel after de-convolution using the sum of general order kinetics and a component for tunnelling recombination. Radiat. Meas. 26, 297–305. Mesterhazy, D., Osvay, M., Kovacs, A., Kelemen, A., 2012. Accidental and retrospective dosimetry using TL method. Radiat. Phys. Chem. 8, 1525–1527. Morehouse, K.M., Ku, Y., 1993. Identification of irradiated foods by monitoring radiolytically produced hydrocarbons. Radiat. Phys. Chem. 42 (1–3), 359–362. Morehouse, K.M., Ku, Y., Albrecht, H.L., Yang, G.C., 1991. Gas chromatographic and electron spin resonance investigations of gamma-irradiated frog legs. Radiat. Phys. Chem. 38, 61–68. Mrozik, A., Marczewska, B., Bilski, P., Gieszczyk, W., 2014. Investigation of OSL signal of resistors from mobile phones for accidental dosimetry. Radiat. Meas. 71, 466–470. Oduko, J.M., Spyrou, N.M., 1990. Thermoluminescence of irradiated foodstuffs. Int. J. Radiat. Appl. Instrum. C Radiat. Phys. Chem. 36 (5), 603–607. Pelicia, K., Garcia, E.A., Molino, A.B., Santos, G.C., Vieira Filho, J.A., Santos, T.A., Berto, D.A., 2015. Chicken meat submitted to gamma radiation and packed with or without oxygen. Brazilian Journal of Poultry Science 17 (2), 255–262. Polymeris, G.S., Goudouri, O.M., Kontonasaki, E., Paraskevopoulos, K.M., Tsirliganis, N. C., Kitis, G., 2011. Thermoluminescence as a probe in bioactivity studies; the case of 58S sol-gel bioactive glass. J. Phys. D Appl. Phys. 44 (39), 1–8. Pradhan, A.S., Kim, J.L., Lee, J.I., 2012. Use of ubiquitous materials for the estimation of accidental exposures. J. Med. Phys. 37 (3), 121–123. Roman-Lopez, J., Correcher, V., Garcia-Guinea, J., Rivera, T., Lozano, I.B., 2014. Thermal and electron stimulated luminescence of natural bones, commercial hydroxyapatite and collagen. Spectrochim. Acta A Mol. Biomol. Spectrosc. 120, 610–615. Romanyukha, A., Trompier, F., Reyes, R.A., Christensen, D.M., Iddins, C.J., Sugarman, S. L., 2014. Electron paramagnetic resonance radiation dose assessment in fingernails of the victim exposed to high dose as result of an accident. Radiat. Environ. Biophys. 53 (4), 755–762. Sahiner, E., Meriç, N., Polymeris, G.S., 2015. Impact of different mechanical pretreatment to the EPR signals of human fingernails towards studying dose response and fading subjected to UV exposure or beta irradiation. Radiat. Meas. 82, 40–46. Trompier, F., Kornak, L., Calas, C., Romanyukha, A., Leblanc, B., Mitchell, C.A., Swartz, H., Clairand, I., 2007. Protocol for emergency EPR dosimetry in fingernails. Radiat. Meas. 42, 1085–1088.
4. Conclusions Chicken bones were investigated with optically stimulated lumi nescence in order to identify their potential luminescent properties which would allow their use as dosimeters in accidental/retrospective/ forensic and/or food post-sterilization dosimetry. In general the OSL sensitivity is low. In addition, bones exhibit sensitization in the first two consecutive cycles up to 50% which remains practically stable for the next irradiation/stimulation cycles. In any case optical bleaching of the sample for 60 min under the light of a solar simulator is capable to empty all traps and restore the sample to its initial state (before any irradiation). Results indicate that the OSL dose response is linear for doses up to ~1.0 kGy, while response over the entire dose range up to several kGy can be fitted with an exponential saturation curve. The lower limit of detection has been found equal to ~18 Gy which is quite high in order to use chicken bones as emergency dosimeter. Loss of the OSL signal is about 50% seven days after irradiation, when samples are kept in dark (fading). The remained stored signal remains stable for longer time periods up to two months post-irradiation in dark conditions. This is important, since bones are not directly exposed to light (protected by the skin and flesh) or to high tempera tures, thus they could be used at post-sterilization and retrospective dosimetry. Moreover, the fading behavior could be fitted using a secondorder kinetic decay function. A dose recovery test was also conducted using the SARHS protocol in order to investigate if the protocol is capable of calculating the sterili zation/accidental dose of irradiated chicken/poultry. The “sterilization” doses were recovered with small errors, thus further validating the protocol. The findings are very promising towards the use of bones in order to identify irradiated food containing bones and/or the use of chicken bones as accidental dosimeters, while the SARHS protocol can be applied for the correct estimation of the sterilization/accidental dose. Acknowledgement The present work was supported by the project "Computational Science and Technologies: Data, Content and Interaction"/"Technolo gies for Content Analysis in Culture", MIS code 5002437, co-financed by Greece (General Secretariat for Research & Technology) and European Union in the framework of the Operational Programme "Competitive ness, Entrepreneurship and Innovation" 2014-2020.
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Wieser, A., Goksu, H.Y., Regulla, D.F., Vogenauer, A., 1994. Limits of retrospective accident dosimetry by EPR and TL with natural materials. Radiat. Meas. 23 (2–3), 509–514. Zarate-Medina, J., Sandoval-Cede~ no, K.J., Barrera-Villatoro, A., Lemus-Ruiz, J., RiveraMontalvo, T., 2015. Thermal effect on thermoluminescence response of hydroxyapatite. Appl. Radiat. Isot. 100, 50–54.
Zdravkova, M., Crokart, N., Trompier, F., Beghein, N., Gallez, B., Debuyst, R., 2004. Non invasive determination of the irradiation dose in fingers using low frequency EPR. Phys. Med. Biol. 49, 2891–2898.
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