|Year : 2021 | Volume
| Issue : 2 | Page : 98-102
Thermoluminescence and optically stimulated luminescence studies of Indian soils for its application in retrospective dosimetry
SN Menon, Sonal Y Kadam
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Submission||06-Apr-2021|
|Date of Decision||16-Jun-2021|
|Date of Acceptance||05-Aug-2021|
|Date of Web Publication||23-Oct-2021|
S N Menon
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
Optically stimulated luminescence (OSL) of quartz obtained from ceramics, concrete, and soil has been studied extensively for its use in retrospective dosimetry. The OSL properties of quartz separated from surface soil of different parts of India were investigated for its application as a retrospective dosimeter. Different parameters such as recuperation, recycling ratio, equivalent dose plateau, and relevant to single-aliquot regenerative protocol were investigated. The dose recovery tests were also performed. These studies show that the soil samples can be used for dose evaluation during any radiation accident.
Keywords: Optically stimulated luminescence, retrospective dosimetry, single-aliquot regenerative, soil, thermoluminescence
|How to cite this article:|
Menon S N, Kadam SY. Thermoluminescence and optically stimulated luminescence studies of Indian soils for its application in retrospective dosimetry. Radiat Prot Environ 2021;44:98-102
|How to cite this URL:|
Menon S N, Kadam SY. Thermoluminescence and optically stimulated luminescence studies of Indian soils for its application in retrospective dosimetry. Radiat Prot Environ [serial online] 2021 [cited 2022 Jun 28];44:98-102. Available from: https://www.rpe.org.in/text.asp?2021/44/2/98/329141
| Introduction|| |
Thermoluminescence (TL) and optically stimulated luminescence (OSL) dosimetry are being routinely used to measure the absorbed dose. Retrospective dosimetry is used to measure the absorbed dose to the individuals during any nuclear/radiological accident. Retrospective dosimetry has been mainly undertaken using (i) cytogenetic and genetic techniques (ii) physical techniques such as electron spin resonance (ESR) dosimetry using enamel of tooth and luminescence dosimetry (TL and OSL), and (iii) computational techniques. These techniques are applicable depending on the severity of any nuclear or radiological accident. Various materials found in the surrounding as well as persons are being explored as accident dosimeter. However, quartz extracted from building materials which have undergone heat treatment is the major mineral employed in TL/OSL-based retrospective dosimetry.,, Investigation of unheated building materials such as concrete and mortar have also been carried out for its use as a retrospective dosimeter., The sensitivity of quartz extracted from fired materials is found to be higher than that of quartz extracted from unheated materials.
Quartz extracted from surface soil was also investigated for its application in retrospective dosimetry.,, Quartz is a major mineral in the soil. The properties of quartz depends on its origin and nature of formation. The provenance of quartz is indicative of that of the sediments. TL, ESR, and crystallinity index of quartz have been suggested as markers for provenance.,, Potential of using TL and OSL properties of quartz as a marker for provenance is under investigation.
Single-aliquot regenerative (SAR) protocol is generally employed to assess the retrospective dose. However, the materials used to measure the dose should satisfy certain criteria to be able to employ SAR protocol. This paper reports the studies carried out in soils collected from the different states in India to see the feasibility of using the quartz separated from them for dose evaluation using SAR during radiation emergencies. Two sand samples collected from beaches at different locations were also investigated. These samples were collected from the city limits and beaches where people frequently visit.
| Materials and Methods|| |
Soil samples were collected from the different parts of India, namely, Jaipur (26.9124° N, 75.7873° E, Rajasthan), Manipal (13.3490° N, 74.7856° E, Karnataka), Siliguri (26.7271° N, 88.3953° E, West Bengal), and Nagpur (21.1458° N, 79.0882° E, Maharashtra) in India from a depth of 0 to 5 cm using SS tubes. Sand samples from beach in Visakhapatnam (17.6868° N, 83.2185° E, Telangana) and Puri (19.8135° N, 85.8312° E, Orissa) were also collected. The samples are denoted as J, M, S, N, V, and P, respectively. The soil samples were cleaned with deionized water and then treated with hydrochloric acid (20%), hydrogen peroxide, hydrofluoric acid (40%) for 40 min, and hydrochloric acid (10%) to obtain a pure sample of quartz. Grains of dimensions between 105 and 210 μm were used for TL and OSL studies. The quartz sample thus obtained was optically bleached to remove the existing TL/OSL signal, if any, due to the natural radiation. To confirm the absence of feldspar, the OSL of samples were recorded at room temperature with IR stimulation. No OSL signal was observed during IR stimulation. The absence of signal confirms that the sample is free of feldspar contamination.
The TL and continuous wave OSL measurements were performed in an automatic Risø TL/OSL reader (TL-DA-20) having a Hoya U-340 optical filter (with peak transmission at ~340 nm and FWHM ~80 nm) at the detection side. The samples were stimulated with the light photons from blue LED present in the Risø reader. The stimulation intensity was set at 72 mW/cm2. A 90Sr/90Y β-source with a dose rate of 20 mGy/s available in the reader was used for the irradiation of the samples. The signal of the first two channels (channel width = 0.25 s) minus the average counts of the last 20 channels of the shine down curve was used for analysis. The OSL was obtained at 125°C in all cases unless specified.
| Results and Discussion|| |
Thermoluminescence and optically stimulated luminescence
The mass normalized TL glow curves recorded with Hoya U-340 optical filter in the Risø system is shown in [Figure 1]. The glow curves were recorded at a heating rate of 1°C/s. The TL peaks were seen at ~90°C (peak 1), ~150°C (peak 2), ~180°C (peak 3), and a wide peak around 275°C (peak 4). The sensitivity of the composite peak at about 275°C was found to be maximum for sample N. This composite peak includes the peak which is associated with the main OSL trap.
|Figure 1: TL glow curve of samples recorded without Hoya U 340 filter in the emission side in Risø reader. The heating rate is 1°C/s and the administered dose is 5 Gy. TL: Thermoluminescence|
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[Figure 2] shows the mass normalized CW-OSL signal obtained for the studied five quartz specimens for a period of 40 s. The decay curves were normalized with the most sensitive sample (N) and are given in the inset of [Figure 2]. As in the case of TL the OSL signal of this sample was large as compared to other samples. Deconvolution of the OSL signal was carried out with CW-OSL formalism.
|Figure 2: Mass normalized OSL decay curves of quartz separated from soil. The OSL curves were recorded at 125°C. The inset shows the normalized OSL curves with the first data point of sample N, the most sensitive one. OSL: Optically stimulated luminescence|
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Where p=σφCW, “öCW” the photoionization cross-section (cm2), “:” incident photon flux (cm−2/s), “p:” stimulation rate (s−1), and n: concentration of electrons in the trap (cm−3). The best fit of the decay curve was achieved with the three first-order components for J, M, V, S, and P. The photoionization cross-sections of the decay components are summarized in [Table 1]. The values of the cross-sections were in agreement with the cross sections reported for quartz.
|Table 1: Photoionization cross section of the traps responsible for fast, medium, and slow components of the continuous wave-optically stimulated luminescence decay curve|
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The cross-sections are termed fast, medium, and slow. The charges released from the main OSL trap contributes to the rapid bleachable component of the OSL which gives rise to the fast component. SAR protocol uses this fast component for the dose measurement. The dominance of fast component in the OSL signal leads to accurate estimation of dose using SAR protocol. It has been reported that the absence of substantial fast component in glacigenic sediments from Scotland has led to the overestimation of dose. The percentage of the fast component in the OSL signal for samples J, M, V, S, P, and N was found to be around 73%, 43%, 90%, 94%, 86%, and 82%, respectively. The presence of a significant fraction of this component shows that these samples are amenable to SAR protocol.
Low-temperature peaks present in quartz will lead to inaccurate estimation of dose due to the unstable signal. To address this problem, the sample is preheated to a certain temperature in SAR protocol. However, repeated heating of the sample can cause sensitivity changes in quartz. The change in sensitivity is corrected using the OSL signal from the sample to a known dose (test dose). The preheat during these cycles can also cause transfer of charges from traps which are insensitive to light to the main OSL center. To find a suitable preheat temperature (PHT) the samples are exposed to a known dose (equivalent dose) and SAR protocol with different PHTs is applied to evaluate this dose. Appropriate PHTs which can cause minimal thermal transfer of charges which lead to correct equivalent dose evaluation are selected.
The equivalent dose plateau curve is plotted for all the samples for the PHT up to 300°C (five number of aliquots were used for each data point) and is as shown in [Figure 3]. Cut heat temperature was kept at 160°C for this experiment. It is seen from the figure that there is a good correlation between the delivered and evaluated dose in all the specimens for the PHT <260°C. However, for temperatures above 260°C, the doses were overestimated in all the samples. Accordingly, the samples were subjected to a preheat treatment of 260°C and a cut heat of 160°C in all the further analysis.
|Figure 3: Plot of measured dose for different preheat temperatures in the range 180°C–300°C. The broken line shows the dose delivered in laboratory. A cut heat of 160°C was used in Single-aliquot regenerative protocol|
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Dose response curve
The useful range of dose where the dosimeter can be used depends on the dose response of the material. SAR protocol with a test dose of 200 mGy was employed to plot the sensitization corrected dose response. The preheat and cut heat temperature was 260°C and 160°C, respectively. The samples were exposed to 0.2, 0.4, 0.8, 1.5, 2, 5, 10, 15, 20, 25, and 30 Gy. [Figure 4] shows the sensitization corrected (Lx/Tx) dose response of the samples. Four aliquots were used for each dose point. It can be seen from the figure that all the samples can be used for dose determination in the range of 200 mGy to 10 Gy. However, in the case of samples J, S, and V the dose range can be extended up to 30 Gy.
|Figure 4: Optically stimulated luminescence versus dose response curve of the samples. The administered dose was in the range from 200 to 30,000 mGy|
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The samples were administered a range of known laboratory doses and the SAR protocol with 200 mGy as test dose was used to evaluate these doses. Regenerative doses were chosen according to the doses to be estimated.
[Table 2] shows the comparison of the laboratory dose and the evaluated dose along with the recuperation and recycling ratios. It can be seen that the estimated dose was within ±20% in the case of low dose. The possible reason for this deviation may be due to the low luminescence sensitivity of the quartz extracted from the soil. The low sensitivity is due to the fact that the quartz has not seen any high temperature. However, there is an improvement in the accuracy of the estimated dose in the case of higher doses. The recycling ratio (0.94–1.03) and recuperation (0.5–5.3) were found to be within the acceptable limits indicative of the fact that the samples can be utilized for measuring the retrospective dose.
|Table 2: Dose recovery test carried out on the samples. The preheat was 260°C and cut heat was 160°C|
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| Conclusions|| |
Several materials found in the surroundings or in person have been studied for its use in accident dosimetry. The feasibility of using quartz separated from surface soil from different locations in India was investigated. All the samples were found to have substantial fast OSL component and all the parameters such as recycling ratio, recuperation, and plateau test relevant to SAR were found to be suitable for the use of the samples for dose assessment. The dose recovery studies carried out have shown that the quartz extracted from the soil can be used as a retrospective dosimeter. The dose response studies of all the samples show that all the samples can be used to determine dose in the range 200 mGy to 10 Gy. These studies are useful for dose evaluation of the public in case of any radiation emergency.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]