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The potential of luminescence signals from electronic components for accident dosimetry
Radiation Measurements 56 (2013) 384e388
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
The potential of luminescence signals from electronic components for accident dosimetry A. Pascu, S. Vasiliniuc*, M. Zeciu-Dolha, A. Timar-Gabor Faculty of Environmental Science and Engineering, Babes-Bolyai University, Fantanele 30, 400294 Cluj-Napoca, Romania
h i g h l i g h t s OSL investigations of electronic components as accident dosimeters. Resistors and chip card modules exhibit highly linear dose response. Initial fading measurements for resistors support accident dosimetry applications. Chip card modules are highly sensitive and relatively homogeneous.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 October 2012 Received in revised form 12 January 2013 Accepted 19 March 2013
This study investigated the optically stimulated luminescence of a large number of electronic components extracted from both old and new generation mobile phones and chip modules of phone cards. Most resistors and all chip modules studied present a linear dose response (R > 0.99) in the dose range investigated (200 mGy up to 6 Gy, respectively 10 Gy), while capacitors, inductors and integrated circuits generally have a non-linear growth (exponential or cubic). For our experimental setup, an average specific luminescence of w20,000 cts in 2 s/Gy (n ¼ 10) and w6000 cts in 2 s/Gy (n ¼ 14) was obtained for two types of chip modules with a relatively high degree of homogeneity (relative standard deviation of 23% and 31%) and a minimum detectable dose of 7 mGy for immediate measurement. The investigated signals show small sensitivity changes (generally <10%) after repeated cycles of irradiation and readout. Preliminary fading measurements are presented. It can be concluded that most mobile phones and phone card components have a significant potential as retrospective luminescence dosimeters. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: OSL Electronic components Chip card modules Accident dosimetry
1. Introduction In the aftermath of a radiological accident or terrorist attack, rapid and accurate assessments of absorbed doses of exposed individuals are imperative for an appropriate triage before medical treatment. The methods used in accident dosimetry for dose reconstruction include biological, physical, and computational techniques (Ainsbury et al., 2010). The established luminescence methods used for retrospective dose assessment use ceramic materials containing quartz and feldspars, such as bricks, tiles and porcelains collected from local buildings (Bailiff, 1997; Bailiff et al., 2000, 2004a,b; Banerjee et al., 2000; Göksu and Bailiff, 2006; Hashimoto et al., 2006). In addition to building materials, several studies suggest the potential usage of household and workplace * Corresponding author. Tel.: þ42 0 774 130 863; fax: þ40 264 307 032. E-mail addresses: [email protected], [email protected] (S. Vasiliniuc). 1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.03.013
chemicals for accident dosimetry (Thomsen et al., 2002; Spooner et al., 2012). Furthermore, a variety of personal objects were proposed in the past ten years to serve as fortuitous dosimeters. Chip card modules found in mobile phones, bankcards, ID or health insurance cards (Göksu, 2003; Mathur et al., 2007; Woda and Spöttl, 2009; Cauwels et al., 2010; Woda et al., 2012) and electronic components, such as resistors, capacitors, inductors, resonators, and diodes removed from mobile phones, portable media player and USB flash drive (Inrig et al., 2008; Beerten et al., 2009; Woda et al., 2009, 2010; Fiedler and Woda, 2011; Ekendahl and Judas, 2012; Trompier et al., 2012) were investigated as emergency dosimeters using luminescence techniques. This study focuses on the pertinent optically stimulated luminescence (OSL) properties of various electronic components and chip card modules, in order to contribute to the documentation of such materials for accident dosimetry purposes. The advantages of such objects (mobile phones, bankcards, wrist watches) are given by their general public use and close proximity of the body.
A. Pascu et al. / Radiation Measurements 56 (2013) 384e388
2. Materials and methods Electronic components extracted from eleven mobile phones, one wrist watch and 31 phone cards (SIM cards) were analysed in this study. The mobile phones belong to different brands and models, nine of them of old generation (2001e2007) and two more recent (2010). Sample preparation was done by removing the electronic components from the circuit board of the mobile phones, and the chip modules from the cards, without using any chemical treatments. The components extracted from mobile phones were resistors, capacitors, inductors, integrated circuits and one light emitting diode (LED). After mechanical extraction, the samples were classified according to their type and manufacturer and placed in stainless steel cups. For each aliquot a variable number of components were used, depending on the size of the components being studied. Electronic components containing an alumina substrate were measured with the radiation sensitive side facing upwards. OSL measurements of the samples were performed with a Risø TL/OSL Luminescence Reader model TL/OSL-DA-20. Optical stimulation was performed using 28 blue LEDs, emitting at 470 nm with a total power of 36 mW/cm2. The stimulation time was 100 s and no thermal treatments were applied as it was desired to use the same measurement protocol for all investigated components. While in the case of alumina rich components (resistors, inductors, and resonators) most studies available in literature used a thermal treatment (10 s preheat at 120 C e Inrig et al., 2008; 10 s preheat at 100 C Beerten et al., 2009; Woda et al., 2010) and stimulation at approximately 100 C in the case of chip card modules, previous studies recommend using no thermal treatments (Woda and Spöttl, 2009). The light detection system consists of a bialkali EMI 9235QA photomultiplier tube (PMT), and a UV detection filter (Hoya U-340; 270e370 nm). Irradiations were performed using the built-in 90 Sr/90Y beta source whose dose rate was calibrated using
385
calibration quartz from Risø. The dose rate was roughly estimated at 0.1 Gy/s considering that Woda and Spöttl (2009) explained that at least in the case of chip card modules using the same dose rate as for coarse calibration quartz is an appropriate approximation. The signals used for calculations were integrated over the first 2 s of stimulation minus a background evaluated from the last 2 s. A similar integration window was used by Cauwels et al. (2010) observing that the fast component, responsible for 60% of the OSL signal, is found in the first 2.1 s of the OSL curve. 3. Results and discussion 3.1. Preliminary tests We analysed a representative selection of electronic components removed from the circuit boards of the old generation mobile phones. In addition, we selected seven phone cards and one microchip removed from a wrist watch. The total number of samples investigated was 41. All the samples investigated exhibited OSL signal after irradiation with 1 Gy, the brightness of the signal varying widely between the types of the components. In order to construct the dose response curve, a modified single-aliquot regenerative-dose (SAR) protocol was used (see Murray and Wintle, 2000; Banerjee et al., 2000). For each sample five doses were applied using the integrated beta source, namely 0.5, 1, 2, 4 and 6 Gy, followed by the measurement of the signal for a nil dose (0 Gy) and a repeat dose (2 Gy). The resistors and the newer generation SIM cards described a linear dose response curve for doses from 0.5 Gy up to 6 Gy, meanwhile the remaining electronic components response showed either cubic or exponentially saturating behaviour. The zero dose signal measured after constructing the dose response growth is used to evaluate the recuperation of the signal following multiple irradiationereadout cycles. Most of the
Fig. 1. OSL decay curves of (a) Samsung GTB3310 resistors and (b) LG KU990i capacitors. The OSL signal of unexposed sample (native signal) is compared to that obtained following beta-irradiation with 1.2 Gy. OSL dose response growth curve of (c) Samsung GTB3310 resistors and (d) LG KU990i capacitors in the dose range of interest (0.3e10 Gy). Resistors type “2” represent intermediate size (code 2, 2 1 mm).
386
A. Pascu et al. / Radiation Measurements 56 (2013) 384e388
tested samples (38) showed an OSL recuperation signal under 10% in comparison with the signal measured following a 1 Gy irradiation. The lack of significant OSL signals to a zero dose administered in the measurement protocol following an irradiation to a high dose in the case of most components sustain the choice of the measurement protocol. 3.2. Electronic components removed from new generation mobile phones 3.2.1. OSL signal and dose response Resistors, capacitors and integrated circuits extracted from two new generation mobile phones (LG KU990i and Samsung GTB3310) showed a considerable OSL signal after irradiation with 1.2 Gy with values between 860 and 694,000 cts in 0.4 s/Gy. Representative OSL signals are presented in Fig. 1a and b for resistors and capacitors, respectively. The resistors exhibit a linear dose response characteristic in the studied dose range (0.3e10 Gy; Fig. 1c) similar to the dose response observed by Inrig et al. (2008). For the investigated integrated circuits, the dose response was cubic, while the capacitors showed three different behaviours e linear (Fig. 1d), exponentially saturating and exponentially associated. The zero-dose signal obtained after constructing the dose response growth curve was approximately 10% of the 1.2 Gy dose signal for resistors while the capacitors showed signal recuperation considerably smaller, less than 1%. 3.2.2. Signal repeatability In order to check the possible presence of sensitivity variations caused by irradiation, after raising the growth curves up to 10 Gy the samples were subjected to eleven repeated irradiationereadout cycles using a constant dose of 2 Gy and no delay time between irradiations and read-out. The signal in each measurement cycle was then normalized to the initial response, which was obtained when constructing the growth curve, the results indicating small sensitivity changes for all the tested samples (generally less than 10%, see Fig. 2). 3.2.3. Fading Laboratory fading measurements were performed for the resistors extracted from new generation mobile phones. The samples were irradiated with a dose of 2 Gy and stored in the darkroom to avoid any light induced signal loss. The optical stimulation was performed after varying delay times following irradiation (1, 2, 5 and 6 days, respectively). In addition, sensitivity variations caused by irradiation were monitored using two prompt irradiations of 2 Gy delivered after each delayed readout process. The results indicate a pronounced signal loss during the first day after irradiation (up to w70% of the initial signal; Table 1) while sensitivity changes are below 5%. 3.3. Chip modules from SIM cards 3.3.1. OSL signal and dose response Chip modules extracted from two batches of unused phone cards (Orange SIM1, n ¼ 10 and Orange SIM2, n ¼ 14) were further investigated. These samples exhibit an intense OSL signal following 1 Gy irradiation (see Fig. 3a). For both types negligible signals of unexposed samples were observed in accordance with Cauwels et al. (2010). Dose linearity was observed as reported in previous studies (see Mathur et al., 2007; Cauwels et al., 2010; Woda et al., 2012). Fig. 3b presents the average dose response curves for SIM2 type of chip modules. Signal recuperation calculated using the response to a nil dose (see Section 3.1) was 2.83 0.3% (n ¼ 10;
Fig. 2. Sensitivity variations of (a) Samsung GTB3310 resistors and (b) LG KU990i capacitors following repeated irradiationereadout cycles using a constant dose of 2 Gy. Reported values represent normalized data to the first measurement during the construction of the doseeresponse curve. The dashed lines (eye guide) indicate a 10% deviation from unity.
SIM1) of the signal recorded at 1 Gy, and 8.3 1.1% (n ¼ 14; SIM2) respectively. 3.3.2. Sensitivity and homogeneity The sensitivity of the chip modules corresponds to the slope of the dose response, as it was found that they follow a linear growth for the dose interval of interest. An average specific luminescence of w20,000 (n ¼ 10) and w6000 (n ¼ 14) cts in 2 s/Gy was calculated for SIM1 and SIM2 chip modules respectively, with a relatively high degree of homogeneity (relative standard deviation of 23 and 31%, respectively). Table 1 Signal loss determined following varying storage periods for the resistors removed from new generation mobile phones. Resistors type “1” are small size (code 1, 1 0.5 mm), while type “2” represent intermediate size (code 2, 2 1 mm). Electronic components
Signal loss after different time delays since irradiation (days) 1
2
5
6
Resistors1 LG KU990i Resistors2 LG KU990i Resistors1 Samsung GTB3310
70% 74% 67%
71% 76% 73%
76% 81% 74%
77% 82% 79%
A. Pascu et al. / Radiation Measurements 56 (2013) 384e388
387
potentially be used as accident dosimeters. A high linearity of the dose response together with negligible sensitivity changes were observed for resistors extracted from mobile phones and chip card modules. While further investigations on the optimization of the measurement protocol regarding thermal treatments, fading behaviour and correction methods remain to be done, it can be concluded that this type of components would allow a reliable extrapolation of signal loss over short irradiationereadout time intervals in large-scale accident scenarios. Acknowledgements A. Pascu gratefully acknowledges the financial support from a scientific performance grant of Babes-Bolyai University, ClujNapoca. The authors thank Dr. Robert Begy for technical assistance during sample preparation. References
Fig. 3. (a) OSL decay curve of Orange SIM2 chip module. The OSL signal of unexposed sample (native signal) is compared to that obtained following beta-irradiation with 1 Gy (b) OSL dose response. Each data point represents an average signal obtained on fourteen aliquots. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3.3.3. Minimum detectable dose As no signals of unexposed samples have been observed, the minimum detectable dose was estimated (for SIM 1) as the dose for which the signal is three times the standard deviation of the background. The background signal was averaged for the ten investigated chip card modules in the flat region of the OSL signal (last 2 s of stimulation) (see Mathur et al., 2007; Sholom et al., 2011). A value of 7 mGy was obtained for immediate read-outs. This value is in accordance with other previous studies on chip cards modules (Woda and Spöttl, 2009e3 mGy; Cauwels et al., 2010e2 mGy). 3.3.4. Signal reproducibility In order to verify the signal reproducibility, the dose response of SIM2 modules was constructed using decreasing doses from 6 to 0.2 Gy, followed by the measurement of the signal for a nil dose (0 Gy) and a repeat dose (2 Gy). The results indicate the same linear doseeresponse relationship as for increasing irradiations, with R2 > 0.99. 4. Conclusions The luminescence characteristics of different types of electronic components from personal objects indicate that such materials can
Ainsbury, E.A., Bakhanova, E., Barquinero, J.F., Brai, M., Chumak, V., Correcher, V., Darroudi, F., Fattibene, P., Gruel, G., Guclu, I., Horn, S., Jaworska, A., Kulka, U., Lindholm, C., Lloyd, D., Longo, A., Marrale, M., Monteiro Gil, O., Oestreicher, U., Pajic, J., Rakic, B., Romm, H., Trompier, F., Veronese, I., Voisin, P., Vral, A., Whitehouse, C.A., Wieser, A., Woda, C., Wojcik, A., Rothkamm, K., 2010. Review of retrospective dosimetry techniques for external ionising radiation exposures. Rad. Prot. Dosim. 147, 1e20. Bailiff, I.K., 1997. Retrospective dosimetry with ceramics. Radiat. Meas. 27, 923e941. Bailiff, I.K., Bøtter-Jensen, L., Correcher, V., Delgado, A., Göksu, H.Y., Jungner, H., Petrov, S.A., 2000. Absorbed dose evaluations in retrospective dosimetry: methodological developments using quartz. Radiat. Meas. 32, 609e613. Bailiff, I.K., Stepanenko, V.F., Göksu, H.Y., Bøtter-Jensen, L., Brodski, L., Chumak, V., Correcher, V., Delgado, A., Golikov, V., Jungner, H., Khamidova, L.G., Kolizshenkov, T.V., Likhtarev, I., Meckbach, R., Petrov, S.A., Sholom, S., 2004a. Comparison of retrospective luminescence dosimetry with computational modelling in two highly contaminated settlements down-wind of the Chernobyl NPP. Health Phys. 86, 25e41. Bailiff, I.K., Stepanenko, V.F., Göksu, H.Y., Jungner, H., Balmukhanov, S.B., Balmukhanov, T.S., Khamidova, L.G., Kisilev, V.I., Kolyado, I.B., Kolizshenkov, T.V., Shoikhet, Y.N., Tsyb, A.F., 2004b. The application of retrospective luminescence dosimetry in areas affected by fallout from the Semipalatinsk nuclear test site: an evaluation of potential. Health Phys. 87, 625e634. Banerjee, D., Bøtter-Jensen, L., Murray, A.S., 2000. Retrospective dosimetry: estimation of the dose to quartz using the single-aliquot regenerative-dose protocol. Appl. Radiat. Isot. 52, 831e844. Beerten, K., Woda, C., Vanhavere, F., 2009. Thermoluminescence dosimetry of electronic components from personal objects. Radiat. Meas. 44, 620e625. Cauwels, V., Beerten, K., Vanhavere, F., Lievens, L., 2010. Accident dosimetry using chipcards. In: Third European IRPA Congress 2010, Helsinki, Finland. Ekendahl, D., Judas, L., 2012. Retrospective dosimetry with alumina substrates from electronic components. Radiat. Prot. Dosim. 150, 134e141. Fiedler, I., Woda, C., 2011. Thermoluminescence of chip inductors from mobile phones for retrospective and accident dosimetry. Radiat. Meas. 46, 1862e1865. Göksu, H.Y., 2003. Telephone chip-cards as individual dosimeters. Radiat. Meas. 37, 617e620. Göksu, H.Y., Bailiff, I.K., 2006. Luminescence dosimetry using building materials and personal objects. Radiat. Prot. Dosim. 119, 413e420. Hashimoto, T., Fujita, H., Sakaue, H., Nakata, Y., Nomura, S., 2006. Comparison of accumulated doses in quartz and feldspar extracts from atomic bombexposed roof tiles using several luminescence methods. Radiat. Meas. 41, 1015e1019. Inrig, E.L., Godfrey-Smith, D.I., Khanna, S., 2008. Optically stimulated luminescence of electronic components for forensic, retrospective, and accident dosimetry. Radiat. Meas. 43, 726e730. Mathur, V.K., Barkyoumb, J.H., Yukihara, E.G., Göksu, H.Y., 2007. Radiation sensitivity of memory chip module of an ID card. Radiat. Meas. 42, 43e48. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiat. Meas. 32, 57e73. Sholom, S., DeWitt, R., Simon, S.M., Bouville, A., McKeever, S.W.S., 2011. Emergency optically stimulated luminescence dosimetry using different materials. Radiat. Meas., 1866e1869. Spooner, N.A., Smith, B.W., Creighton, D.F., Questiaux, D., Hunter, P.G., 2012. Luminescence from NaCl for application to retrospective dosimetry. Radiat. Meas. 47, 883e889. Thomsen, K.J., Bøtter-Jensen, L., Murray, A.S., 2002. Household and workplace chemicals as retrospective luminescence dosemeters. Radiat. Prot. Dosim. 101, 515e518. Trompier, F., Fattibene P., Woda, C., Bassinet, C., Bortolin, E., De Angelis, C., Della Monaca, S., Viscomi, D., Wieser, A., 2012. Retrospective dose assessment in a
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radiation mass casualty by EPR and OSL in mobile phones. In: 13th International Congress of the International Radiation Protection Association, Glasgow, United Kingdom. Woda, C., Spöttl, T., 2009. On the use of OSL of wire-bond chip card modules for retrospective and accident dosimetry. Radiat. Meas. 44, 548e553. Woda, C., Bassinet, C., Trompier, F., Bortolin, E., Della Monaca, S., Fattibene, P., 2009. Radiation-induced damage analysed by luminescence methods in
retrospective dosimetry and emergency response. Ann. Ist. Super. Sanità 45, 297e306. Woda, C., Greilich, S., Beerten, K., 2010. On the OSL curve shape and preheat treatment of electronic components from portable electronic devices. Radiat. Meas. 45, 746e748. Woda, C., Fiedler, I., Spӧttl, T., 2012. On the use of OSL of chip card modules with molding for retrospective and accident dosimetry. Radiat. Meas. 47, 1068e1073.
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
The potential of luminescence signals from electronic components for accident dosimetry A. Pascu, S. Vasiliniuc*, M. Zeciu-Dolha, A. Timar-Gabor Faculty of Environmental Science and Engineering, Babes-Bolyai University, Fantanele 30, 400294 Cluj-Napoca, Romania
h i g h l i g h t s OSL investigations of electronic components as accident dosimeters. Resistors and chip card modules exhibit highly linear dose response. Initial fading measurements for resistors support accident dosimetry applications. Chip card modules are highly sensitive and relatively homogeneous.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 October 2012 Received in revised form 12 January 2013 Accepted 19 March 2013
This study investigated the optically stimulated luminescence of a large number of electronic components extracted from both old and new generation mobile phones and chip modules of phone cards. Most resistors and all chip modules studied present a linear dose response (R > 0.99) in the dose range investigated (200 mGy up to 6 Gy, respectively 10 Gy), while capacitors, inductors and integrated circuits generally have a non-linear growth (exponential or cubic). For our experimental setup, an average specific luminescence of w20,000 cts in 2 s/Gy (n ¼ 10) and w6000 cts in 2 s/Gy (n ¼ 14) was obtained for two types of chip modules with a relatively high degree of homogeneity (relative standard deviation of 23% and 31%) and a minimum detectable dose of 7 mGy for immediate measurement. The investigated signals show small sensitivity changes (generally <10%) after repeated cycles of irradiation and readout. Preliminary fading measurements are presented. It can be concluded that most mobile phones and phone card components have a significant potential as retrospective luminescence dosimeters. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: OSL Electronic components Chip card modules Accident dosimetry
1. Introduction In the aftermath of a radiological accident or terrorist attack, rapid and accurate assessments of absorbed doses of exposed individuals are imperative for an appropriate triage before medical treatment. The methods used in accident dosimetry for dose reconstruction include biological, physical, and computational techniques (Ainsbury et al., 2010). The established luminescence methods used for retrospective dose assessment use ceramic materials containing quartz and feldspars, such as bricks, tiles and porcelains collected from local buildings (Bailiff, 1997; Bailiff et al., 2000, 2004a,b; Banerjee et al., 2000; Göksu and Bailiff, 2006; Hashimoto et al., 2006). In addition to building materials, several studies suggest the potential usage of household and workplace * Corresponding author. Tel.: þ42 0 774 130 863; fax: þ40 264 307 032. E-mail addresses: [email protected], [email protected] (S. Vasiliniuc). 1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.03.013
chemicals for accident dosimetry (Thomsen et al., 2002; Spooner et al., 2012). Furthermore, a variety of personal objects were proposed in the past ten years to serve as fortuitous dosimeters. Chip card modules found in mobile phones, bankcards, ID or health insurance cards (Göksu, 2003; Mathur et al., 2007; Woda and Spöttl, 2009; Cauwels et al., 2010; Woda et al., 2012) and electronic components, such as resistors, capacitors, inductors, resonators, and diodes removed from mobile phones, portable media player and USB flash drive (Inrig et al., 2008; Beerten et al., 2009; Woda et al., 2009, 2010; Fiedler and Woda, 2011; Ekendahl and Judas, 2012; Trompier et al., 2012) were investigated as emergency dosimeters using luminescence techniques. This study focuses on the pertinent optically stimulated luminescence (OSL) properties of various electronic components and chip card modules, in order to contribute to the documentation of such materials for accident dosimetry purposes. The advantages of such objects (mobile phones, bankcards, wrist watches) are given by their general public use and close proximity of the body.
A. Pascu et al. / Radiation Measurements 56 (2013) 384e388
2. Materials and methods Electronic components extracted from eleven mobile phones, one wrist watch and 31 phone cards (SIM cards) were analysed in this study. The mobile phones belong to different brands and models, nine of them of old generation (2001e2007) and two more recent (2010). Sample preparation was done by removing the electronic components from the circuit board of the mobile phones, and the chip modules from the cards, without using any chemical treatments. The components extracted from mobile phones were resistors, capacitors, inductors, integrated circuits and one light emitting diode (LED). After mechanical extraction, the samples were classified according to their type and manufacturer and placed in stainless steel cups. For each aliquot a variable number of components were used, depending on the size of the components being studied. Electronic components containing an alumina substrate were measured with the radiation sensitive side facing upwards. OSL measurements of the samples were performed with a Risø TL/OSL Luminescence Reader model TL/OSL-DA-20. Optical stimulation was performed using 28 blue LEDs, emitting at 470 nm with a total power of 36 mW/cm2. The stimulation time was 100 s and no thermal treatments were applied as it was desired to use the same measurement protocol for all investigated components. While in the case of alumina rich components (resistors, inductors, and resonators) most studies available in literature used a thermal treatment (10 s preheat at 120 C e Inrig et al., 2008; 10 s preheat at 100 C Beerten et al., 2009; Woda et al., 2010) and stimulation at approximately 100 C in the case of chip card modules, previous studies recommend using no thermal treatments (Woda and Spöttl, 2009). The light detection system consists of a bialkali EMI 9235QA photomultiplier tube (PMT), and a UV detection filter (Hoya U-340; 270e370 nm). Irradiations were performed using the built-in 90 Sr/90Y beta source whose dose rate was calibrated using
385
calibration quartz from Risø. The dose rate was roughly estimated at 0.1 Gy/s considering that Woda and Spöttl (2009) explained that at least in the case of chip card modules using the same dose rate as for coarse calibration quartz is an appropriate approximation. The signals used for calculations were integrated over the first 2 s of stimulation minus a background evaluated from the last 2 s. A similar integration window was used by Cauwels et al. (2010) observing that the fast component, responsible for 60% of the OSL signal, is found in the first 2.1 s of the OSL curve. 3. Results and discussion 3.1. Preliminary tests We analysed a representative selection of electronic components removed from the circuit boards of the old generation mobile phones. In addition, we selected seven phone cards and one microchip removed from a wrist watch. The total number of samples investigated was 41. All the samples investigated exhibited OSL signal after irradiation with 1 Gy, the brightness of the signal varying widely between the types of the components. In order to construct the dose response curve, a modified single-aliquot regenerative-dose (SAR) protocol was used (see Murray and Wintle, 2000; Banerjee et al., 2000). For each sample five doses were applied using the integrated beta source, namely 0.5, 1, 2, 4 and 6 Gy, followed by the measurement of the signal for a nil dose (0 Gy) and a repeat dose (2 Gy). The resistors and the newer generation SIM cards described a linear dose response curve for doses from 0.5 Gy up to 6 Gy, meanwhile the remaining electronic components response showed either cubic or exponentially saturating behaviour. The zero dose signal measured after constructing the dose response growth is used to evaluate the recuperation of the signal following multiple irradiationereadout cycles. Most of the
Fig. 1. OSL decay curves of (a) Samsung GTB3310 resistors and (b) LG KU990i capacitors. The OSL signal of unexposed sample (native signal) is compared to that obtained following beta-irradiation with 1.2 Gy. OSL dose response growth curve of (c) Samsung GTB3310 resistors and (d) LG KU990i capacitors in the dose range of interest (0.3e10 Gy). Resistors type “2” represent intermediate size (code 2, 2 1 mm).
386
A. Pascu et al. / Radiation Measurements 56 (2013) 384e388
tested samples (38) showed an OSL recuperation signal under 10% in comparison with the signal measured following a 1 Gy irradiation. The lack of significant OSL signals to a zero dose administered in the measurement protocol following an irradiation to a high dose in the case of most components sustain the choice of the measurement protocol. 3.2. Electronic components removed from new generation mobile phones 3.2.1. OSL signal and dose response Resistors, capacitors and integrated circuits extracted from two new generation mobile phones (LG KU990i and Samsung GTB3310) showed a considerable OSL signal after irradiation with 1.2 Gy with values between 860 and 694,000 cts in 0.4 s/Gy. Representative OSL signals are presented in Fig. 1a and b for resistors and capacitors, respectively. The resistors exhibit a linear dose response characteristic in the studied dose range (0.3e10 Gy; Fig. 1c) similar to the dose response observed by Inrig et al. (2008). For the investigated integrated circuits, the dose response was cubic, while the capacitors showed three different behaviours e linear (Fig. 1d), exponentially saturating and exponentially associated. The zero-dose signal obtained after constructing the dose response growth curve was approximately 10% of the 1.2 Gy dose signal for resistors while the capacitors showed signal recuperation considerably smaller, less than 1%. 3.2.2. Signal repeatability In order to check the possible presence of sensitivity variations caused by irradiation, after raising the growth curves up to 10 Gy the samples were subjected to eleven repeated irradiationereadout cycles using a constant dose of 2 Gy and no delay time between irradiations and read-out. The signal in each measurement cycle was then normalized to the initial response, which was obtained when constructing the growth curve, the results indicating small sensitivity changes for all the tested samples (generally less than 10%, see Fig. 2). 3.2.3. Fading Laboratory fading measurements were performed for the resistors extracted from new generation mobile phones. The samples were irradiated with a dose of 2 Gy and stored in the darkroom to avoid any light induced signal loss. The optical stimulation was performed after varying delay times following irradiation (1, 2, 5 and 6 days, respectively). In addition, sensitivity variations caused by irradiation were monitored using two prompt irradiations of 2 Gy delivered after each delayed readout process. The results indicate a pronounced signal loss during the first day after irradiation (up to w70% of the initial signal; Table 1) while sensitivity changes are below 5%. 3.3. Chip modules from SIM cards 3.3.1. OSL signal and dose response Chip modules extracted from two batches of unused phone cards (Orange SIM1, n ¼ 10 and Orange SIM2, n ¼ 14) were further investigated. These samples exhibit an intense OSL signal following 1 Gy irradiation (see Fig. 3a). For both types negligible signals of unexposed samples were observed in accordance with Cauwels et al. (2010). Dose linearity was observed as reported in previous studies (see Mathur et al., 2007; Cauwels et al., 2010; Woda et al., 2012). Fig. 3b presents the average dose response curves for SIM2 type of chip modules. Signal recuperation calculated using the response to a nil dose (see Section 3.1) was 2.83 0.3% (n ¼ 10;
Fig. 2. Sensitivity variations of (a) Samsung GTB3310 resistors and (b) LG KU990i capacitors following repeated irradiationereadout cycles using a constant dose of 2 Gy. Reported values represent normalized data to the first measurement during the construction of the doseeresponse curve. The dashed lines (eye guide) indicate a 10% deviation from unity.
SIM1) of the signal recorded at 1 Gy, and 8.3 1.1% (n ¼ 14; SIM2) respectively. 3.3.2. Sensitivity and homogeneity The sensitivity of the chip modules corresponds to the slope of the dose response, as it was found that they follow a linear growth for the dose interval of interest. An average specific luminescence of w20,000 (n ¼ 10) and w6000 (n ¼ 14) cts in 2 s/Gy was calculated for SIM1 and SIM2 chip modules respectively, with a relatively high degree of homogeneity (relative standard deviation of 23 and 31%, respectively). Table 1 Signal loss determined following varying storage periods for the resistors removed from new generation mobile phones. Resistors type “1” are small size (code 1, 1 0.5 mm), while type “2” represent intermediate size (code 2, 2 1 mm). Electronic components
Signal loss after different time delays since irradiation (days) 1
2
5
6
Resistors1 LG KU990i Resistors2 LG KU990i Resistors1 Samsung GTB3310
70% 74% 67%
71% 76% 73%
76% 81% 74%
77% 82% 79%
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potentially be used as accident dosimeters. A high linearity of the dose response together with negligible sensitivity changes were observed for resistors extracted from mobile phones and chip card modules. While further investigations on the optimization of the measurement protocol regarding thermal treatments, fading behaviour and correction methods remain to be done, it can be concluded that this type of components would allow a reliable extrapolation of signal loss over short irradiationereadout time intervals in large-scale accident scenarios. Acknowledgements A. Pascu gratefully acknowledges the financial support from a scientific performance grant of Babes-Bolyai University, ClujNapoca. The authors thank Dr. Robert Begy for technical assistance during sample preparation. References
Fig. 3. (a) OSL decay curve of Orange SIM2 chip module. The OSL signal of unexposed sample (native signal) is compared to that obtained following beta-irradiation with 1 Gy (b) OSL dose response. Each data point represents an average signal obtained on fourteen aliquots. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3.3.3. Minimum detectable dose As no signals of unexposed samples have been observed, the minimum detectable dose was estimated (for SIM 1) as the dose for which the signal is three times the standard deviation of the background. The background signal was averaged for the ten investigated chip card modules in the flat region of the OSL signal (last 2 s of stimulation) (see Mathur et al., 2007; Sholom et al., 2011). A value of 7 mGy was obtained for immediate read-outs. This value is in accordance with other previous studies on chip cards modules (Woda and Spöttl, 2009e3 mGy; Cauwels et al., 2010e2 mGy). 3.3.4. Signal reproducibility In order to verify the signal reproducibility, the dose response of SIM2 modules was constructed using decreasing doses from 6 to 0.2 Gy, followed by the measurement of the signal for a nil dose (0 Gy) and a repeat dose (2 Gy). The results indicate the same linear doseeresponse relationship as for increasing irradiations, with R2 > 0.99. 4. Conclusions The luminescence characteristics of different types of electronic components from personal objects indicate that such materials can
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