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OSL studies of commonly available medicines for their use as retrospective dosimeters
Radiation Measurements 101 (2017) 7e12
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Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
OSL studies of commonly available medicines for their use as retrospective dosimeters S.N. Menon*, A.K. Singh, S.Y. Kadam, D.K. Koul, D. Datta Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai-85, India
h i g h l i g h t s Retrospective dosimetry using artificial materials. OSL from medicines. Medicines can be used as a fortuitous dosimeter.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 September 2016 Received in revised form 6 April 2017 Accepted 25 April 2017 Available online 27 April 2017
Luminescence properties of artificial objects have been reported worldwide for their potential application in retrospective dosimetry. In this study the feasibility of utilizing the optically stimulated luminescence (OSL) emission of four commonly available medicinal tablets in India for retrospective dosimetry was explored. The nature of OSL emission, dose response, reusability, dose recovery and absence of fading after 24 h of storage demonstrated the ability of the studied samples to act as emergency dosimeters in the dose range of 1e30 Gy. © 2017 Published by Elsevier Ltd.
Keywords: Retrospective dosimetry OSL Medicines Dose recovery
1. Introduction Stimulated luminescence phenomena, thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) dosimetry has been widely used in dosimetric applications. The phosphor once irradiated, naturally or artificially, produce luminescence by stimulation with heat and light called as TL and OSL respectively. The emissions occur due to recombination of charge, released from the traps due to these stimulations, with the luminescence centre. The various centres participating in the luminescence process are populated with charge due to irradiation, natural or artificial. The intensity of the emission depends on the magnitude of dose the phosphor has received prior to the read out. Reliable methodology using standard phosphors has been established in conventional personnel and environmental dosimetry. However, one branch of dosimetry, the retrospective
* Corresponding author. E-mail address: [email protected] (S.N. Menon). http://dx.doi.org/10.1016/j.radmeas.2017.04.018 1350-4487/© 2017 Published by Elsevier Ltd.
dosimetry, involve dose mapping outside controlled area and guarded perimeter of a nuclear facility. This mode of dosimetry is used when conventional dosimeters are not available in the public domain during huge radiation fallout due to some major accident, like recent breakdown of nuclear reactors in Fukushima, Japan. The doses received by workers, emergency respondents and public require retrospective dose assessment in order to recover missing dosimetric information, specifically during the early phase of the accident. Retrospective dosimetry techniques commonly used for this purpose are (i) biodosimetry (ii) EPR dosimetry with tooth enamel and (iii) TL/OSL dosimetry. Quartz extracted from materials found in buildings, such as ceramics has been established as a reliable material for retrospective dosimetry using TL/OSL techniques (ICRU, 2002; Singh et al., 2016). In case of a radiological accident or mass casualty events it becomes important to identify materials of interest for medical triage. A variety of materials, like chips from telephone and credit cards, electronic components from cell phones, electronic resistors, money bills, common salt, garments, tooth enamel, desiccants etc., have been tried for retrospective dosimetry using their TL/OSL
8
S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
2. Materials and methods
Fig. 1. The photograph of the medicines tablets Crocin® (M1), Paracad® (M2), Ultramol® (M3), Calcium with Vitamin D3® (M4) manufactured by Glaxo Smithline, Zydus Cadilla, Aristo Pharmaceuticals and Elder Pharmaceuticals, respectively.
emissions (Druzhyna et al., 2016; Geber-Bergstrand et al., 2015; € ksu, 2003; Inrig et al., 2008; Mathur et al., 2007; Sholom and Go €ttl, 2009; McKeever, 2014; Spooner et al., 2012; Woda and Spo Yukihara et al., 2007). However, dose measurement using such materials has been a challenge due to lack of sensitivity, sample-tosample variability, and fading of the OSL signal after irradiation (Sholom et al., 2011). Fading, in particular, complicates the problem because of the need to determine correction factors and to account for sample-to-sample variability in the properties. This mode of dosimetry involves a rough estimation about the exposure due to an accident and, therefore, the tolerance for error can be large. In this study, feasibility of using OSL signal of commonly used four medicinal tablets in India for retrospective dosimetry has been attempted. A few papers are available on the studies of OSL properties of medicinal tablets for the purpose of dosimetry (Kazakis et al., 2014; Sholom and Mckeever, 2016). OSL characterization of these samples suggested that the samples to be well behaving and having a prominent fast OSL component. The dose response and dose recovery with wide range of administered dose values suggested that the OSL signal of the studied tablets is useful for retrospective dosimetry.
Commonly available medicines in Indian house hold were selected for the analysis. The medicines investigated were Crocin®, Paracad®, Ultramol® and Calcium with Vitamin D3® tablets manufactured by Glaxo Smithline, Zydus Cadilla, Aristo Pharmaceuticals and Elder Pharmaceuticals, respectively, and shown in Fig. 1 These medicines is hereafter denoted as M1, M2, M3 and M4 respectively in the text. All the tablets were crushed in a mortar before the experiments. In case of tablets with protective coating, it was scrapped off prior to the crushing process. The measurement were carried out on powdered samples adhered to 10 mm diameter stainless discs with silicone spray. Several batches of the above medicines were investigated. The luminescence measurements were carried in an automatic Risø TL/OSL, TL-DA-20 system (Bøtter-Jensen et al., 2003) having blue light-emitting diodes (l ¼ 470 ± 30 nm) as stimulation source. The power level was set at 90% of the maximum stimulation intensity of 80 mW/cm2. It can accommodate 48 samples and has onplate attached b-irradiator. The detection filter used in all observations was Hoya U-340 (Ip ~ 340 nm, FWHM ~ 80 nm). Irradiation of the samples was carried out using a90Sr/90Y b-source having dose rate 20 mGy/s housed in the system. The OSL was recorded with stimulation at room temperature for 100 s. The signal consisted of integrated counts during initial 1 s (each data point corresponds to 0.25 s) subtracted by the average counts during the last 5 s of the decay curve. Fading studies were carried out by storing the aliquots carrying the sample in dark outside the instrument after an exposure of 2 Gy with in situ beta source. The protocol was managed in such a way that the discs were read on the same day so as to avoid any day-to-day variation of the system, though it is expected to be negligible.
3. Results and discussion 3.1. OSL characteristics The CW-OSL shine down curves of the samples M1, M2, M3 and M4 were recorded at room temperature immediately after exposure to 2 Gy. The CW-OSL shine down curve of an un - irradiated sample of M1 was also recorded. The experiment showed that all drugs are OSL sensitive with dominant fast component. The mass normalised OSL decay curves of the samples are shown in Fig. 2. For a better comparison, the data of all the five curves were divided by the initial data point of the sample M4, the most sensitive OSL sample among the four studied samples. There was no discernable signal above the background noise from un-irradiated samples. It can be seen from Fig. 2 that the OSL sensitivities of the medicines varied widely between the formulations. The main ingredient of M1, M2 and M3 is paracetamol however the variation in sensitivity between these samples is due to the other ingredients present in the medicines (Sholom and Mckeever, 2016). Though the exact origin of the OSL signals are not known usually inorganic
Table 1 Photo ionization cross-section of the traps responsible for fast, medium and slow components of the CW-OSL decay curve. Sample Fig. 2. CW-OSL shine down curves of the samples M1, M2, M3 and M4 recorded immediately after exposure to 2 Gy and unirradiated sample of M1 (curve Bg in Figure). For a better comparison, the data of all the five curves were divided by the initial data point of the sample M4, the most sensitive OSL sample among the four studied samples.
M1 M2 M3 M4
Photo-ionization cross-section (cm2) Fast
Medium
Slow
2.38E-17 1.21E-17 3.99E-17 2.28E-17
1.26E-18 9.44E-19 3.67E-18 1.08E-18
2.29E-20 3.07E-20 1.04E-20 2.83E-20
S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
9
CW-OSL equation (Yukihara and McKeever, 2011):
ICW ¼ nfeft
(1)
where f ¼ s fCW , ‘s’ is the photo-ionization cross-section, ‘fCW ’ is the simulating light flux, ‘f ’ is known as optical excitation rate and n is the initial number of trapped electron. The input parameters were varied for different number of components, incorporated in the deconvolution process, and the resulting values of figure of merit were checked for best fitting. Based on results, three first order CW-OSL components were found to be the best fit for the recorded CW-OSL decay curves of all the samples. The photo ionization cross sections for different components are listed in Table 1. The fast component was estimated to be very dominant in case of three out of four samples studied here, its contribution being 82, 45, 92 and 82% for M1, M2, M3 an M4 respectively. The abundance of the fast component ensures the easy bleachability of the sample, which is very important for reusability of the material. Attempt was made to record the TL of the medicinal tablets. However, all the studied medicines could not sustain temperature beyond 80 C and were charred probably due to the presence of excipients in the sample. This posed a limitation in recording the glow curves of the samples. 3.2. Dose response The dose response of the medicines was investigated by irradiating the samples with doses of 1, 2, 5, 10, 15, 20, 25 and 30 Gy and recording the OSL signal immediately at room temperature. The growth curve, i.e. plot of OSL signal versus dose, for samples M1, M2, M3 and M4 is shown in Fig. 3. The OSL signal was integrated for first 1 s and for background subtraction average OSL signal of last 5 s was used. Each point in the plot represents the average value of OSL measurements using three aliquots. The dose response of the samples was observed to be linear over the dose range applied in this study, 1e30 Gy, except for sample M1. In case of this sample the linearity of the response extended up to 25 Gy only, as shown in Fig. 3. Kazakis et al. had observed a second order polynomial and a power function fit for doses beyond 50 Gy in case of Panadol, a drug containing paracetamol. The linear dose range demonstrated by the samples is very relevant for retrospective dosimetry. However, it might be noted that all these medicines showed appreciable OSL
Fig. 3. Dose response plots of the different medicines M1, M2, M3 and M4. The values reported in the plots were obtained as the means of the integrated counts of three different aliquots.
compounds show good TL/OSL signals as compared to organic compounds. The high sensitivity of M4 sample, Calcium with Vitamin D3®, might be due to the presence of calcium compound in the formulation. The CW-OSL decay curve was de-convoluted using first order
Fig. 4. The effect of humidity on dose response of the samples M1, M2, M3 and M4. The tablets were stored in a humid environment for seven days before irradiation with a dose of 10 Gy and thereafter the OSL was recorded with blue light at room temperature The OSL intensity of first second is represented by the bars. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 6. CW-OSL decay curves of the two aliquots, irradiated and un-irradiated, of sample M1 recorded with blue light at room temperature. The irradiated aliquot was exposed to a dose of 6 Gy. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
signal, i.e. five times above the background signal, only if the delivered dose was >1 Gy. So, the limitation of estimating doses below 1 Gy does exist with the medicinal tablets used in this study. To calculate the minimum detectable dose, 10 aliquots of the medicines were used for background variation measurement. The minimum detectable dose was found out to be 250, 275,120 and 150 mGy for M1,M2, M3 and M4 respectively (dose corresponding to 3s of the background). The effect of humidity on OSL intensity of the samples was also studied and the results are shown in Fig. 4. The tablets were stored in a humid environment for seven days before irradiation and the OSL was recorded. The relative humidity as measured by a hygrometer was 80% throughout the storage period. Other set of tablets were dried in an oven at 50 C for around half an hour. There was no change in OSL intensity in the case of samples M1 and M4, as can be seen from Fig. 4. But, the OSL intensity was reduced by the enhancement in the humidity for M2 and M3 samples (Fig. 4). 3.3. Fading of the signal with storage time
Fig. 5. The fading of the OSL signal for M1, M2, M3 and M4 observed up to a time duration of 10 days. A dose of 2 Gy was administered to the aliquots and, thereafter, they were stored for different time durations at room temperature before OSL measurement at room temperature. The inset shows the fading of the signals up to a time period of 24 h since irradiation treatment.
The fading of the OSL signal for all the samples was studied up to a time duration of 10 days. A dose of 2 Gy was administered to the aliquots and stored in dark for different time durations at room temperature and then stimulated with blue light to record OSL at room temperature. The OSL signals of samples M1, M2, M3 and M4 were plotted as a function of storage time and are shown in Fig. 5. Interestingly, fading of the signal was seen to be negligible after one day of exposure in case of three samples out of the four studied here. In fact, the fading till a time delay of few hours since irradiation was found to be significant, as shown in the inset of Fig. 5, and the signals stabilized thereafter. The absence of fading of the signals in three out of the four studied medicines after a storage time of twenty four hours is a big advantage in using these medicines for retrospective dosimetry, as the presence of continuous fading has been the main problem in case of various materials tried for retrospective dosimetry. It is worth noting here that the sample M3 demonstrated an increase of OSL signal with the storage time. This is probably due to the charge transfer from traps corresponding to lower temperature TL peaks to the OSL sensitive trap at room temperature. Such phenomenon has been observed for many phosphors, like quartz (Aitken, 1998).
S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
11
Table 2 OSL background counts of fresh, un-irradiated, and irradiated aliquots of samples stimulated with blue light at room temperature for 100 s. The backgrounds consist of average of the counts during the last 5 s of the CW-OSL decay curves. Sample Background counts of un-irradiated Background counts of irradiated sample (counts/sec) sample (counts/sec) M1 M2 M3 M4
159 184 194 408
± ± ± ±
6.2 8.7 6.3 13
169 173 186 412
± ± ± ±
5.9 6.6 6.2 6.3
3.4. Reusability The reusability of the phosphor, essentially, involves observing (i) the degree of the bleachability of sample and (ii) the change in the sensitivity of the sample with multiple runs. This study was carried out by irradiating the discs of all the samples to 6 Gy dose and then recording OSL for 100 s at room temperature. The OSL measurement was also done with fresh, un-irradiated, discs of all the samples. The decay curves of the two discs, irradiated and unirradiated, of sample M1 are plotted in Fig. 6. Comparing the two curves in this figure it can be seen that OSL signal of irradiated sample after few tens of seconds matches with the signal from unirradiated sample. Same trend was seen in case of all the samples as is depicted in Table 2. The table shows the OSL intensity (average of the last 5 s) of the fresh and exposed samples. These results implied that the OSL signals of the medicinal tablets studied here are easily bleachable. To see any variation in the sensitivity of the samples with multiple runs, ten consecutive measurements involving administering a dose of 6 Gy and, subsequent, recording of CW-OSL decay curve were undertaken. A change of about ±8% in sensitivity was observed for 5 cycles of irradiation, and optical stimulation and is as shown in Fig. 7. Also, some samples demonstrated reproducibility beyond 5 cycles. The results of this observation ensured the reusability of the medicinal tablets for dosimetric applications. 3.5. Dose recovery The dose recovery is a very important test to check the feasibility of a phosphor for dose estimation. It involves estimation of an administered dose, called unknown dose, from the calibration curve. The fading characteristics of M3 (Fig. 5.) show that the dose recovery in this sample will lead to incorrect dose estimation and this might be true for certain other medicines. Therefore dose recovery was attempted only in M1, M2 and M4. The samples were divided in to two parts; one part was irradiated to a unknown dose (laboratory dose of 3 and 10 Gy in this case) and the other part was used to generate a calibration curve by exposing the aliquots made from it to different doses of 2, 6, 18 and 24 Gy. The OSL of all the aliquots was recorded twenty four hours after irradiation with blue light at room temperature. The unknown doses, estimated using the calibration curve, for the three samples are shown in Table 3. The estimated dose values of all the samples were recovered with a precision of 10% at 1s. This observation reinforced the reliability of the medicinal tablets for accident dosimetry. 4. Conclusions Four commonly used medicines in Indian households were investigated for their potential use as emergency dosimeters. The nature of OSL emission, dose response, reusability, dose recovery and absence of fading after 24 h demonstrated the ability of the medicinal tablets to act as emergency dosimeters in the dose range
Fig. 7. Sensitivity variation of the samples with multiple runs involving administering a dose of 6 Gy and subsequent recording of CW-OSL decay curve.
of 1e30 Gy. The stability of the signal after few hours of storage after radiation exposure offers good advantage over other materials
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S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
Table 3 Dose recovery for samples M1, M2 and M4. Delivered dose (Gy)
3 10
Estimated dose (Gy) M1
M2
M4
3.1 ± 0.15 10.25 ± 0.3
2.7 ± 0.18 9.51 ± 0.19
3.3 ± 0.19 10.48 ± 0.28
used so far for this mode of dosimetry. However in case of sample M3 an increase of the OSL signal was observed with the storage time. This type of behaviour may lead to incorrect estimation of dose if appropriate corrections are not employed. Such phenomenon has been observed for many other materials. Acknowledgements The authors are grateful to Dr. K.S. Pradeepkumar, Associate Director, Health Safety & Environment Group, BARC for the support and encouragement during the course of this work. References Aitken, M.J., 1998. An Introduction to Optical Dating. Oxford University Press. Bøtter-Jensen, L., Anderson, C.E., Duller, G.A.T., Murray, A.S., 2003. Developments in radiation, stimulation and observation facility in luminescence measurements. Radiat. Meas. 37, 535e541. Druzhyna, S., Datz, H., Horowitz, Y.S., Oster, L., Orion, I., 2016. Thermo- luminescence characteristics of Israeli household salts for retrospective dosimetry in radiological events. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact.
Mater. Atoms 377, 67e76. €f, C.L., Geber-Bergstrand, T., Bernhardsson, C., Christiansson, M., Mattsson, S., R€ aa 2015. Desiccants for retrospective dosimetry using optically stimulated luminescence (OSL). Radiat. Meas. 78, 17e22. €ksu, H.Y., 2003. Telephone chip-cards as individual dosemeters. Radiat. Meas. 37, Go 617e620. Inrig, L., Godfrey-Smith, D.I., Khanna, S., 2008. Optically stimulated luminescence of electronic components for forensic, retrospective and accident dosimetry. Radiat. Meas. 43, 726e730. International Commission on Radiological Units and Measurements, 2002. Retrospective assessment of exposure to ionising radiation (Report 68). J. ICRU 2. Kazakis, N.A., Tsirliganis, N.C., Kitis, G., 2014. Preliminary thermoluminescence and optically stimulated luminescence investigation of commercial pharmaceutical preparations towards the drug sterilization dosimetry. Appl. Radiat. Isot 91, 79e91. €ksu, H.Y., 2007. Radiation sensitivity Mathur, V.K., Barkyoumb, J.H., Yukihara, E.G., Go of memory chip module of an ID card. Radiat. Meas. 42, 43e48. Sholom, S., Mckeever, S.W.S., 2016. Emergency EPR and OSL dosimetry with table vitamins and minerals. Radiat. Prot. Dosim. 172 (1e3), 139e144. Sholom, S., McKeever, S.W.S., 2014. Emergency OSL dosimetry with common place materials. Radiat. Meas. 61, 33e51. Sholom, S., DeWitt, R., Simon, S.L., Bouville, A., McKeever, S.W.S., 2011. Emergency optically stimulated luminescence dosimetry using different materials. Radiat. Meas. 46, 1866e1869. Singh, A.K., Menon, S.N., Kadam, S.Y., Koul, D.K., Datta, D., 2016. OSL studies of local bricks for retrospective dosimetric application. Nucl. Instrum. Methods Phys. Res. B 383, 14e20. 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. €ttl, T., 2009. On the use of OSL wire-bound chip card modules for Woda, C., Spo retrospective and accident dosimetry. Radiat. Meas. 44, 548e553. Yukihara, E. G., McKeever, S. W. S, 2011. A John Wiley and Sons, Ltd. Publication. Yukihara, E.G., Mittani, J., McKeever, S.W.S., Simon, S.L., 2007. Optically stimulated luminescence (OSL) of dental enamel for retrospective assessment of radiation exposure. Radiat. Meas. 42, 1256e1260.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
OSL studies of commonly available medicines for their use as retrospective dosimeters S.N. Menon*, A.K. Singh, S.Y. Kadam, D.K. Koul, D. Datta Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai-85, India
h i g h l i g h t s Retrospective dosimetry using artificial materials. OSL from medicines. Medicines can be used as a fortuitous dosimeter.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 September 2016 Received in revised form 6 April 2017 Accepted 25 April 2017 Available online 27 April 2017
Luminescence properties of artificial objects have been reported worldwide for their potential application in retrospective dosimetry. In this study the feasibility of utilizing the optically stimulated luminescence (OSL) emission of four commonly available medicinal tablets in India for retrospective dosimetry was explored. The nature of OSL emission, dose response, reusability, dose recovery and absence of fading after 24 h of storage demonstrated the ability of the studied samples to act as emergency dosimeters in the dose range of 1e30 Gy. © 2017 Published by Elsevier Ltd.
Keywords: Retrospective dosimetry OSL Medicines Dose recovery
1. Introduction Stimulated luminescence phenomena, thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) dosimetry has been widely used in dosimetric applications. The phosphor once irradiated, naturally or artificially, produce luminescence by stimulation with heat and light called as TL and OSL respectively. The emissions occur due to recombination of charge, released from the traps due to these stimulations, with the luminescence centre. The various centres participating in the luminescence process are populated with charge due to irradiation, natural or artificial. The intensity of the emission depends on the magnitude of dose the phosphor has received prior to the read out. Reliable methodology using standard phosphors has been established in conventional personnel and environmental dosimetry. However, one branch of dosimetry, the retrospective
* Corresponding author. E-mail address: [email protected] (S.N. Menon). http://dx.doi.org/10.1016/j.radmeas.2017.04.018 1350-4487/© 2017 Published by Elsevier Ltd.
dosimetry, involve dose mapping outside controlled area and guarded perimeter of a nuclear facility. This mode of dosimetry is used when conventional dosimeters are not available in the public domain during huge radiation fallout due to some major accident, like recent breakdown of nuclear reactors in Fukushima, Japan. The doses received by workers, emergency respondents and public require retrospective dose assessment in order to recover missing dosimetric information, specifically during the early phase of the accident. Retrospective dosimetry techniques commonly used for this purpose are (i) biodosimetry (ii) EPR dosimetry with tooth enamel and (iii) TL/OSL dosimetry. Quartz extracted from materials found in buildings, such as ceramics has been established as a reliable material for retrospective dosimetry using TL/OSL techniques (ICRU, 2002; Singh et al., 2016). In case of a radiological accident or mass casualty events it becomes important to identify materials of interest for medical triage. A variety of materials, like chips from telephone and credit cards, electronic components from cell phones, electronic resistors, money bills, common salt, garments, tooth enamel, desiccants etc., have been tried for retrospective dosimetry using their TL/OSL
8
S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
2. Materials and methods
Fig. 1. The photograph of the medicines tablets Crocin® (M1), Paracad® (M2), Ultramol® (M3), Calcium with Vitamin D3® (M4) manufactured by Glaxo Smithline, Zydus Cadilla, Aristo Pharmaceuticals and Elder Pharmaceuticals, respectively.
emissions (Druzhyna et al., 2016; Geber-Bergstrand et al., 2015; € ksu, 2003; Inrig et al., 2008; Mathur et al., 2007; Sholom and Go €ttl, 2009; McKeever, 2014; Spooner et al., 2012; Woda and Spo Yukihara et al., 2007). However, dose measurement using such materials has been a challenge due to lack of sensitivity, sample-tosample variability, and fading of the OSL signal after irradiation (Sholom et al., 2011). Fading, in particular, complicates the problem because of the need to determine correction factors and to account for sample-to-sample variability in the properties. This mode of dosimetry involves a rough estimation about the exposure due to an accident and, therefore, the tolerance for error can be large. In this study, feasibility of using OSL signal of commonly used four medicinal tablets in India for retrospective dosimetry has been attempted. A few papers are available on the studies of OSL properties of medicinal tablets for the purpose of dosimetry (Kazakis et al., 2014; Sholom and Mckeever, 2016). OSL characterization of these samples suggested that the samples to be well behaving and having a prominent fast OSL component. The dose response and dose recovery with wide range of administered dose values suggested that the OSL signal of the studied tablets is useful for retrospective dosimetry.
Commonly available medicines in Indian house hold were selected for the analysis. The medicines investigated were Crocin®, Paracad®, Ultramol® and Calcium with Vitamin D3® tablets manufactured by Glaxo Smithline, Zydus Cadilla, Aristo Pharmaceuticals and Elder Pharmaceuticals, respectively, and shown in Fig. 1 These medicines is hereafter denoted as M1, M2, M3 and M4 respectively in the text. All the tablets were crushed in a mortar before the experiments. In case of tablets with protective coating, it was scrapped off prior to the crushing process. The measurement were carried out on powdered samples adhered to 10 mm diameter stainless discs with silicone spray. Several batches of the above medicines were investigated. The luminescence measurements were carried in an automatic Risø TL/OSL, TL-DA-20 system (Bøtter-Jensen et al., 2003) having blue light-emitting diodes (l ¼ 470 ± 30 nm) as stimulation source. The power level was set at 90% of the maximum stimulation intensity of 80 mW/cm2. It can accommodate 48 samples and has onplate attached b-irradiator. The detection filter used in all observations was Hoya U-340 (Ip ~ 340 nm, FWHM ~ 80 nm). Irradiation of the samples was carried out using a90Sr/90Y b-source having dose rate 20 mGy/s housed in the system. The OSL was recorded with stimulation at room temperature for 100 s. The signal consisted of integrated counts during initial 1 s (each data point corresponds to 0.25 s) subtracted by the average counts during the last 5 s of the decay curve. Fading studies were carried out by storing the aliquots carrying the sample in dark outside the instrument after an exposure of 2 Gy with in situ beta source. The protocol was managed in such a way that the discs were read on the same day so as to avoid any day-to-day variation of the system, though it is expected to be negligible.
3. Results and discussion 3.1. OSL characteristics The CW-OSL shine down curves of the samples M1, M2, M3 and M4 were recorded at room temperature immediately after exposure to 2 Gy. The CW-OSL shine down curve of an un - irradiated sample of M1 was also recorded. The experiment showed that all drugs are OSL sensitive with dominant fast component. The mass normalised OSL decay curves of the samples are shown in Fig. 2. For a better comparison, the data of all the five curves were divided by the initial data point of the sample M4, the most sensitive OSL sample among the four studied samples. There was no discernable signal above the background noise from un-irradiated samples. It can be seen from Fig. 2 that the OSL sensitivities of the medicines varied widely between the formulations. The main ingredient of M1, M2 and M3 is paracetamol however the variation in sensitivity between these samples is due to the other ingredients present in the medicines (Sholom and Mckeever, 2016). Though the exact origin of the OSL signals are not known usually inorganic
Table 1 Photo ionization cross-section of the traps responsible for fast, medium and slow components of the CW-OSL decay curve. Sample Fig. 2. CW-OSL shine down curves of the samples M1, M2, M3 and M4 recorded immediately after exposure to 2 Gy and unirradiated sample of M1 (curve Bg in Figure). For a better comparison, the data of all the five curves were divided by the initial data point of the sample M4, the most sensitive OSL sample among the four studied samples.
M1 M2 M3 M4
Photo-ionization cross-section (cm2) Fast
Medium
Slow
2.38E-17 1.21E-17 3.99E-17 2.28E-17
1.26E-18 9.44E-19 3.67E-18 1.08E-18
2.29E-20 3.07E-20 1.04E-20 2.83E-20
S.N. Menon et al. / Radiation Measurements 101 (2017) 7e12
9
CW-OSL equation (Yukihara and McKeever, 2011):
ICW ¼ nfeft
(1)
where f ¼ s fCW , ‘s’ is the photo-ionization cross-section, ‘fCW ’ is the simulating light flux, ‘f ’ is known as optical excitation rate and n is the initial number of trapped electron. The input parameters were varied for different number of components, incorporated in the deconvolution process, and the resulting values of figure of merit were checked for best fitting. Based on results, three first order CW-OSL components were found to be the best fit for the recorded CW-OSL decay curves of all the samples. The photo ionization cross sections for different components are listed in Table 1. The fast component was estimated to be very dominant in case of three out of four samples studied here, its contribution being 82, 45, 92 and 82% for M1, M2, M3 an M4 respectively. The abundance of the fast component ensures the easy bleachability of the sample, which is very important for reusability of the material. Attempt was made to record the TL of the medicinal tablets. However, all the studied medicines could not sustain temperature beyond 80 C and were charred probably due to the presence of excipients in the sample. This posed a limitation in recording the glow curves of the samples. 3.2. Dose response The dose response of the medicines was investigated by irradiating the samples with doses of 1, 2, 5, 10, 15, 20, 25 and 30 Gy and recording the OSL signal immediately at room temperature. The growth curve, i.e. plot of OSL signal versus dose, for samples M1, M2, M3 and M4 is shown in Fig. 3. The OSL signal was integrated for first 1 s and for background subtraction average OSL signal of last 5 s was used. Each point in the plot represents the average value of OSL measurements using three aliquots. The dose response of the samples was observed to be linear over the dose range applied in this study, 1e30 Gy, except for sample M1. In case of this sample the linearity of the response extended up to 25 Gy only, as shown in Fig. 3. Kazakis et al. had observed a second order polynomial and a power function fit for doses beyond 50 Gy in case of Panadol, a drug containing paracetamol. The linear dose range demonstrated by the samples is very relevant for retrospective dosimetry. However, it might be noted that all these medicines showed appreciable OSL
Fig. 3. Dose response plots of the different medicines M1, M2, M3 and M4. The values reported in the plots were obtained as the means of the integrated counts of three different aliquots.
compounds show good TL/OSL signals as compared to organic compounds. The high sensitivity of M4 sample, Calcium with Vitamin D3®, might be due to the presence of calcium compound in the formulation. The CW-OSL decay curve was de-convoluted using first order
Fig. 4. The effect of humidity on dose response of the samples M1, M2, M3 and M4. The tablets were stored in a humid environment for seven days before irradiation with a dose of 10 Gy and thereafter the OSL was recorded with blue light at room temperature The OSL intensity of first second is represented by the bars. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 6. CW-OSL decay curves of the two aliquots, irradiated and un-irradiated, of sample M1 recorded with blue light at room temperature. The irradiated aliquot was exposed to a dose of 6 Gy. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
signal, i.e. five times above the background signal, only if the delivered dose was >1 Gy. So, the limitation of estimating doses below 1 Gy does exist with the medicinal tablets used in this study. To calculate the minimum detectable dose, 10 aliquots of the medicines were used for background variation measurement. The minimum detectable dose was found out to be 250, 275,120 and 150 mGy for M1,M2, M3 and M4 respectively (dose corresponding to 3s of the background). The effect of humidity on OSL intensity of the samples was also studied and the results are shown in Fig. 4. The tablets were stored in a humid environment for seven days before irradiation and the OSL was recorded. The relative humidity as measured by a hygrometer was 80% throughout the storage period. Other set of tablets were dried in an oven at 50 C for around half an hour. There was no change in OSL intensity in the case of samples M1 and M4, as can be seen from Fig. 4. But, the OSL intensity was reduced by the enhancement in the humidity for M2 and M3 samples (Fig. 4). 3.3. Fading of the signal with storage time
Fig. 5. The fading of the OSL signal for M1, M2, M3 and M4 observed up to a time duration of 10 days. A dose of 2 Gy was administered to the aliquots and, thereafter, they were stored for different time durations at room temperature before OSL measurement at room temperature. The inset shows the fading of the signals up to a time period of 24 h since irradiation treatment.
The fading of the OSL signal for all the samples was studied up to a time duration of 10 days. A dose of 2 Gy was administered to the aliquots and stored in dark for different time durations at room temperature and then stimulated with blue light to record OSL at room temperature. The OSL signals of samples M1, M2, M3 and M4 were plotted as a function of storage time and are shown in Fig. 5. Interestingly, fading of the signal was seen to be negligible after one day of exposure in case of three samples out of the four studied here. In fact, the fading till a time delay of few hours since irradiation was found to be significant, as shown in the inset of Fig. 5, and the signals stabilized thereafter. The absence of fading of the signals in three out of the four studied medicines after a storage time of twenty four hours is a big advantage in using these medicines for retrospective dosimetry, as the presence of continuous fading has been the main problem in case of various materials tried for retrospective dosimetry. It is worth noting here that the sample M3 demonstrated an increase of OSL signal with the storage time. This is probably due to the charge transfer from traps corresponding to lower temperature TL peaks to the OSL sensitive trap at room temperature. Such phenomenon has been observed for many phosphors, like quartz (Aitken, 1998).
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Table 2 OSL background counts of fresh, un-irradiated, and irradiated aliquots of samples stimulated with blue light at room temperature for 100 s. The backgrounds consist of average of the counts during the last 5 s of the CW-OSL decay curves. Sample Background counts of un-irradiated Background counts of irradiated sample (counts/sec) sample (counts/sec) M1 M2 M3 M4
159 184 194 408
± ± ± ±
6.2 8.7 6.3 13
169 173 186 412
± ± ± ±
5.9 6.6 6.2 6.3
3.4. Reusability The reusability of the phosphor, essentially, involves observing (i) the degree of the bleachability of sample and (ii) the change in the sensitivity of the sample with multiple runs. This study was carried out by irradiating the discs of all the samples to 6 Gy dose and then recording OSL for 100 s at room temperature. The OSL measurement was also done with fresh, un-irradiated, discs of all the samples. The decay curves of the two discs, irradiated and unirradiated, of sample M1 are plotted in Fig. 6. Comparing the two curves in this figure it can be seen that OSL signal of irradiated sample after few tens of seconds matches with the signal from unirradiated sample. Same trend was seen in case of all the samples as is depicted in Table 2. The table shows the OSL intensity (average of the last 5 s) of the fresh and exposed samples. These results implied that the OSL signals of the medicinal tablets studied here are easily bleachable. To see any variation in the sensitivity of the samples with multiple runs, ten consecutive measurements involving administering a dose of 6 Gy and, subsequent, recording of CW-OSL decay curve were undertaken. A change of about ±8% in sensitivity was observed for 5 cycles of irradiation, and optical stimulation and is as shown in Fig. 7. Also, some samples demonstrated reproducibility beyond 5 cycles. The results of this observation ensured the reusability of the medicinal tablets for dosimetric applications. 3.5. Dose recovery The dose recovery is a very important test to check the feasibility of a phosphor for dose estimation. It involves estimation of an administered dose, called unknown dose, from the calibration curve. The fading characteristics of M3 (Fig. 5.) show that the dose recovery in this sample will lead to incorrect dose estimation and this might be true for certain other medicines. Therefore dose recovery was attempted only in M1, M2 and M4. The samples were divided in to two parts; one part was irradiated to a unknown dose (laboratory dose of 3 and 10 Gy in this case) and the other part was used to generate a calibration curve by exposing the aliquots made from it to different doses of 2, 6, 18 and 24 Gy. The OSL of all the aliquots was recorded twenty four hours after irradiation with blue light at room temperature. The unknown doses, estimated using the calibration curve, for the three samples are shown in Table 3. The estimated dose values of all the samples were recovered with a precision of 10% at 1s. This observation reinforced the reliability of the medicinal tablets for accident dosimetry. 4. Conclusions Four commonly used medicines in Indian households were investigated for their potential use as emergency dosimeters. The nature of OSL emission, dose response, reusability, dose recovery and absence of fading after 24 h demonstrated the ability of the medicinal tablets to act as emergency dosimeters in the dose range
Fig. 7. Sensitivity variation of the samples with multiple runs involving administering a dose of 6 Gy and subsequent recording of CW-OSL decay curve.
of 1e30 Gy. The stability of the signal after few hours of storage after radiation exposure offers good advantage over other materials
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Table 3 Dose recovery for samples M1, M2 and M4. Delivered dose (Gy)
3 10
Estimated dose (Gy) M1
M2
M4
3.1 ± 0.15 10.25 ± 0.3
2.7 ± 0.18 9.51 ± 0.19
3.3 ± 0.19 10.48 ± 0.28
used so far for this mode of dosimetry. However in case of sample M3 an increase of the OSL signal was observed with the storage time. This type of behaviour may lead to incorrect estimation of dose if appropriate corrections are not employed. Such phenomenon has been observed for many other materials. Acknowledgements The authors are grateful to Dr. K.S. Pradeepkumar, Associate Director, Health Safety & Environment Group, BARC for the support and encouragement during the course of this work. References Aitken, M.J., 1998. An Introduction to Optical Dating. Oxford University Press. Bøtter-Jensen, L., Anderson, C.E., Duller, G.A.T., Murray, A.S., 2003. Developments in radiation, stimulation and observation facility in luminescence measurements. Radiat. Meas. 37, 535e541. Druzhyna, S., Datz, H., Horowitz, Y.S., Oster, L., Orion, I., 2016. Thermo- luminescence characteristics of Israeli household salts for retrospective dosimetry in radiological events. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact.
Mater. Atoms 377, 67e76. €f, C.L., Geber-Bergstrand, T., Bernhardsson, C., Christiansson, M., Mattsson, S., R€ aa 2015. Desiccants for retrospective dosimetry using optically stimulated luminescence (OSL). Radiat. Meas. 78, 17e22. €ksu, H.Y., 2003. Telephone chip-cards as individual dosemeters. Radiat. Meas. 37, Go 617e620. Inrig, L., Godfrey-Smith, D.I., Khanna, S., 2008. Optically stimulated luminescence of electronic components for forensic, retrospective and accident dosimetry. Radiat. Meas. 43, 726e730. International Commission on Radiological Units and Measurements, 2002. Retrospective assessment of exposure to ionising radiation (Report 68). J. ICRU 2. Kazakis, N.A., Tsirliganis, N.C., Kitis, G., 2014. Preliminary thermoluminescence and optically stimulated luminescence investigation of commercial pharmaceutical preparations towards the drug sterilization dosimetry. Appl. Radiat. Isot 91, 79e91. €ksu, H.Y., 2007. Radiation sensitivity Mathur, V.K., Barkyoumb, J.H., Yukihara, E.G., Go of memory chip module of an ID card. Radiat. Meas. 42, 43e48. Sholom, S., Mckeever, S.W.S., 2016. Emergency EPR and OSL dosimetry with table vitamins and minerals. Radiat. Prot. Dosim. 172 (1e3), 139e144. Sholom, S., McKeever, S.W.S., 2014. Emergency OSL dosimetry with common place materials. Radiat. Meas. 61, 33e51. Sholom, S., DeWitt, R., Simon, S.L., Bouville, A., McKeever, S.W.S., 2011. Emergency optically stimulated luminescence dosimetry using different materials. Radiat. Meas. 46, 1866e1869. Singh, A.K., Menon, S.N., Kadam, S.Y., Koul, D.K., Datta, D., 2016. OSL studies of local bricks for retrospective dosimetric application. Nucl. Instrum. Methods Phys. Res. B 383, 14e20. 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. €ttl, T., 2009. On the use of OSL wire-bound chip card modules for Woda, C., Spo retrospective and accident dosimetry. Radiat. Meas. 44, 548e553. Yukihara, E. G., McKeever, S. W. S, 2011. A John Wiley and Sons, Ltd. Publication. Yukihara, E.G., Mittani, J., McKeever, S.W.S., Simon, S.L., 2007. Optically stimulated luminescence (OSL) of dental enamel for retrospective assessment of radiation exposure. Radiat. Meas. 42, 1256e1260.