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On optically stimulated luminescence properties of household salt as a retrospective dosemeter

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Thermoluminescence (TL) and optically stimulated luminescence (OSL) in the UV (270-370 nm) spectral region have been investigated for five types of table salt (NaCl) available in Romanian supermarkets with a view to applying them in retrospective dosimetry. The salt samples gave bright TL signals with two main peaks at ∼100°C and at 300 or 260°C, depending on the origin of the salt and bright OSL signals under continuous stimulation with blue light. The OSL signal (stimulated at 100°C after a pre-heat of 10 s at 150°C) was used for investigations in a standard multiple aliquot procedure. The dose-response was found to be linear in the dose range investigated (up to ∼100 mGy) and the lower limit of detection for the samples varied from ∼0.01 to 14 mGy. These characteristics, along with the widespread abundance and low cost of household salt, confirm its potential as a retrospective dosemeter.
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ON OPTICALLY STIMULATED LUMINESCENCE PROPERTIES OF
HOUSEHOLD SALT AS A RETROSPECTIVE DOSEMETER
Alida Timar-Gabor*, Oana Trandafir
Babeş-Bolyai University, Faculty of Environmental Sciences and Engineering, Cluj-Napoca, Romania
*Corresponding author: alida.timar@ubbcluj.ro; alida_timar@yahoo.com
Faculty of Environmental Science and Engineering, Babeş-Bolyai University, Fântânele 30, 400294 Cluj
Napoca, Romania
Tel: +40 264 405300
Fax: +40 264 591 906
ABSTRACT
Thermoluminescence (TL) and optically stimulated luminescence (OSL) in the UV (270-370 nm) spectral
region have been investigated for five types of table salt (NaCl) available in Romanian supermarkets with the
view to their use in retrospective dosimetry. The salt samples gave bright TL signals with two main peaks at
~100
o
C and at 300
o
C or 260
o
C, depending on the origin of the salt and bright OSL signals under continuous
stimulation with blue light. The OSL signal (stimulated at 100
o
C after a preheat of 10 s at 150
o
C) was used for
investigations in a standard multiple aliquot procedure. The dose response was found to be linear in the dose
range investigated (up to ~ 100 mGy) and the lower limit of detection (LLD) for the samples varied from ~0.01
to 14 mGy. These characteristics, along with the widespread abundance and low cost of household salt, confirm
its potential as a retrospective dosemeter.
KEY WORDS: retrospective dosimetry, OSL, TL, salt (NaCl).
INTRODUCTION
Several methods for retrospective dose assessment have been developed and applied in accident
dosimetry over the past decades, including biological, physical and computational methods
(1,2)
. However,
ongoing research is being carried out to optimize techniques that can overcome common disadvantages, such
as the extensive time period required before obtaining results, high costs, and weak sensitivity at low doses.
Thermoluminescence (TL) and optically stimulated luminescence (OSL) are widespread phenomena
in crystalline solids which contain trapping levels within their band gap. OSL and TL are the luminescence
emitted from an irradiated insulator or semiconductor during exposure to light or heat, respectively. OSL and
TL involve stimulation of electrons, and they are usually accompanied by photoconductivity phenomena. The
luminescence signal emitted is dependent on the irradiation history of the sample. In the case of OSL, the
wavelength of the emitted signal is shorter than the stimulation wavelength
(3)
.
The best established luminescence techniques for the purpose of dose reconstruction are focused on the use of
natural minerals such as quartz and feldspar that can be found in bricks, tiles and pottery collected from local
buildings
(4, 5, 6, 7, 8, 9)
.
Another promising candidate for the role of retrospective dosemeter is salt. The dosimetric
characteristics of various forms of sodium chloride (NaCl) have been investigated, e.g.: analytical quality
NaCl
(10)
, halite (mined rock salt)
(11)
and household salt for cooking purposes
(12,13)
. This alkali halide has a
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band gap of approximately 8.5 eV
(14)
and work on correlating TL and F centres has been reviewed
(3,15)
. The
effect of various dopants on the TL response of NaCl has been investigated more recently
(16,17,18,19)
. Several
techniques have been employed to study the dosimetric properties of salt: infrared stimulated luminescence
(IRSL)
(20)
and radioluminescence (RL)
(20)
, TL and OSL
(3,21)
, OSL
(22)
, TL
(23)
, all of which suggest that salt is a
promising material for application in accident dosimetry.
More recently TL, OSL and IRSL emitted from 19 samples of salt collected from around the world
have been studied
(21,24,25)
. Using TL emission spectroscopy, several emission peaks were observed and a
prominent, and frequently intense, emission peak centered at 590 nm was observed for most samples; many
other samples also exhibited a UV (370 nm) peak. It was concluded
(21)
that the 590 nm TL usually exhibits
much greater sensitivity than does the UV TL. On the other hand, the UV emission of the OSL stimulated by
470 nm showed much greater sensitivity than the blue-to-orange emission stimulated by 880 nm IR
illumination
(21)
.
In the present study, the luminescence (TL and OSL) UV (270-370 nm) emission of different
Romanian brands of salt is presented. The dosimetric properties of the OSL stimulated by blue light (470 nm)
are assessed and compared with previously published data. Special attention is paid to background levels,
specific luminescence and lower limits of detection in order to characterize the properties of these materials as
opportunistic dosimeters.
METHODS AND MATERIALS
The instrument used to perform the measurements presented in this work is a TL/OSL reader, model
Risø TL/OSL-DA-20. It is equipped with 28 blue light emitting diodes (LEDs) emitting at 470 nm with a total
power of 40 mW/cm
2
, which were used as an optical stimulation source for our aliquots of salt. The
stimulation power of the diodes was set to 30% of the maximum power in order to prevent the saturation of
the photomultiplier tube. The light detection system consists of a bialkali EMI 9235QA photomultiplier tube
(PMT), and a UV filter (Hoya U-340; 270-370 nm). The irradiations were performed either using the built-in
90
Sr/
90
Y beta source (dose rate of 0.1 Gy/s), or using an external
60
Co gamma source (dose
rate of 4.3 Gy/h).
The heating rate for TL measurements was 5 °C/s.
Five brands of commercially available salt were studied, all of which are aimed for household use and
were purchased from local supermarkets in Cluj-Napoca. Three of them are mined salts (iodized table rock
salt, extra-refined iodized table rock salt, re-crystallized iodized table rock salt), one is natural iodized sea salt
and one is a salt substitute (containing 1/3 sea salt). Table 1 presents details taken from the packets; E536
(potassium ferrocyanide) and E504 (magnesium carbonate) are anti-caking agents, present in small amounts.
The salt grains were used directly from the packets. Each aliquot consisted of a couple of tens of milligrams of
salt poured into a stainless steel cup. After measurements, the content of each cup was weighed with a high
precision electronic balance for mass normalization, in order to compensate for the variation in the OSL
output due to variation in the amount of salt in each cup.
RESULTS AND DISCUSSIONS
TL signals
All samples of salt gave very bright TL signals with two main peaks, but with some variation (Figure
1). All salt samples show a low temperature peak at ~ 100
o
C. The position of the high temperature peak can
be used to separate the samples into two groups, as previously found
(22)
. The first group includes three rock
salts (a, b and c in Figure 1), which have two peaks above 200°C and a high-temperature peak at around
300
o
C. Similar values for the position of the TL peaks have been presented previously
(13)
, with the intensity
of the peaks varying for different salt types. The TL characteristics of the other two types of salt (d and e in
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Figure 1) are similar, with their high temperature peak at about 260
o
C. The presence of two peaks at around
the same temperatures (heating rate of 5
o
C/s) was also reported for an Alpine salt with iodine
(26)
. An analysis
of 10 Indian brands of salt
(23)
showed that more than two peaks are always visible (heating rate of 10
o
C/s), but
only those at ~250
o
C and above were considered suitable for dosimetry. Another study
(27)
identified the main
dosimetric peak for most of the analysed commercial Greek salt samples to be at approximately 220
o
C
(heating rate 1
o
C/s), while for a natural Turkish salt two distinct dosimetric peaks were observed at ~200
o
C
and ~300
o
C, while other authors
(20)
observed peaks at 180
o
C and 220
o
C (heating rate 5
o
C/s) for natural salt
and only the 220
o
C peak for synthetic NaCl.
Since the low temperature peak is not thermally stable, a preheat treatment is usually used to remove
this peak; for instance, treatments applied in other studies include: a 220
o
C preheat for 10 s
(22)
, a 200
o
C
preheat for 10 s
(26)
, a preheat of 10 s at 150
o
C
(13)
which has also been adopted in this work. The low
temperature peak is erased by applying this thermal treatment, leaving the two higher temperature peaks
(Figure 1). The low temperature peak is also decreased when the TL signal is recorded with a one day delay
after irradiation.
OSL signals
Continuous wave optically stimulated luminescence (CW-OSL) was recorded for 40 s using blue light
(470 nm with constant power 12 mW/cm
2
). This was performed following a preheat (5
o
C/s) of 10 s at 150
o
C,
thus ensuring that the thermally unstable trap (TL peak at about 100
o
C) was kept empty, minimizing the
possibility of charge transfer between the two traps during stimulation. All the samples gave bright OSL
signals following this treatment (Figure 2), similar to those obtained by others
(13,28)
. The OSL signals decayed
rapidly, being reduced to less than 1% of the initial signal in the first 5 s of stimulation, and reached a constant
level for stimulation times over 25 s. As found previously
(28)
, the decay was not exponential.
In order to evaluate the thermal stability of the OSL signals, a pulse annealing experiment was carried
out. Individual aliquots were irradiated with a dose of 400 mGy using the
90
Sr-
90
Y source, and each aliquot
was then heated at a heating rate of 5
o
C/s to different temperatures from 150
o
C to 360
o
C and held at that
temperature for 10 s. Subsequently the OSL signal was measured at 100
o
C. The weight-normalized net OSL
signals (first 0.77 s of blue light stimulation less the background collected from the last 0.77 s of stimulation)
were determined for each aliquot. The average signals for four aliquots for each thermal treatment, normalized
to unity for the first point (anneal at 150
o
C) were plotted as function of annealing temperature. Figures 3a and
b show the results for one mined salt (“R”) and one sea salt (“S”). The two samples show similar behaviour,
with the signal showing relatively little increase for annealing temperatures ranging from 150
o
C to about
200
o
C and then a rapid decrease for temperatures above 220
o
C. This suggests that the OSL signals (stimulated
at 100
o
C) originate from traps deeper than 220
o
C, and are thus suitable for dosimetric applications. This
conclusion is in agreement with another recent study
(24)
.
Dose response and limit of detection
The contribution to the OSL signal from natural background radiation, accumulated during household
storage and resulting from the past history of processing and handling, must be estimated so that it can be
subtracted from the gross OSL signal to obtain the signal contribution from the radiation exposure related to
the accident. Based on analysis of the samples at the time of purchase, negligible background signals were
detected (see Figure 2 for salt type ‘B’); this was especially true for the newly crystallized salts (two sea salts
and one re-crystallized mine salt). For salt type ‘B’, the natural dose was 0.03 mGy (obtained from the two
signals in Figure 2), while for salt type ‘R’, the natural dose was around 10 mGy, compared with 1.3±0.3 mGy
found by others
(13)
.
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For each brand of salt, at least 3 doses were applied using the
60
Co source, namely 12 mGy, 48 mGy
and 96 mGy. In addition, for salt type ‘B’, 10 doses were applied over the same dose range, 12 to 96 mGy
(Figure 4). This dose range is lower than that studied previously, where doses up to 16 Gy
(13)
and 60 Gy
(10)
were used in a single aliquot protocol, or doses up to 9 Gy
(22)
and 35 Gy
(21)
when using a multiple aliquot
approach. The OSL signal per unit mass of the irradiated salt was found to be proportional to the exposure to
ionising radiation. Figure 4 shows the linear dependence between signal and absorbed dose that was observed
in the dose range from 12 to 96 mGy for salt type “B”, as previously observed by other authors
(22)
. This
linearity can be contrasted with the requirement of two components when higher doses were used to construct
a dose response curve
(10,13,21)
. For instance, an analysis of the dose-response relationship reported a rapid rise
in the OSL signal over the initial 10 Gy doses, while a more gentle increase was observed over the following
50 Gy
(10)
. Another study suggests than after only 10 Gy, saturation may be reached
(22)
. High values of the R
2
coefficient of determination were obtained with 0.99 for 3 of the types of salt studied and 0.97 for the other 2
(Table 2). With the exception of salt type B’, three points were used to construct each of the dose response
curves, with each data point representing the average net signal obtained on at least four aliquots.
For doses ranging from 12 to 96 mGy, a generally high sensitivity in terms of luminescence (first 0.77
s) yield per unit absorbed dose and unit mass (termed ‘specific luminescence’) was observed (Table 2) and is
of the same order of magnitude for salt types G, R, B and S. However, it is about an order of magnitude
smaller than found by others
(13)
. The much lower specific luminescence found for salt ‘I’ is partially
explained by the added potassium chloride (66%) that does not seem to present OSL signals for the excitation
band and/or the detection window employed in this study.
The lower limit of detection (LLD) was calculated as being equivalent to three standard deviations of
the mean background signal, divided by the specific luminescence of each salt (LLD = 3σ(OSL
bck
)/c
specific
)
(13,
22)
. The results are shown in the last column in Table 2 and range from 0.008 to 14 mGy. The differences in
the lower limits of detection are mainly caused by the different background doses. Excluding salt type R’,
which showed the highest background signal, all other 4 brands have very low limits of detection (less than 1
mGy). This value is similar to those reported by others: 1 mGy
(13)
, 0.4 mGy
(26)
, 0.2 to 1 mGy
(22)
.
Fading
To investigate fading effects, the material was irradiated with the external
60
Co source and kept in
light-tight packaging. A part of the material was measured immediately after the irradiation. The rest was
stored and the mass-normalized OSL signals were measured after different delay times (Figure 5). Rapid
signal loss took place during the first 7 days (inset to Figure 5); thereafter the signal remained constant at
about 65% of its initial value over the period investigated (30 weeks), thus not reducing its usefulness as a
retrospective dosemeter. The exact cause of this fading is not yet known. Larger fading effects were observed
compared to other studies. For instance, an investigation of the possible anomalous’ fading over a period of
several hours (up to 25) revealed no significant short-term fading
(10)
. Another study
(26)
on the other hand,
reported a fading effect over a period of 20 days, but it was considered insignificant for accident dosimetry, in
agreement with other authors
(13)
.
CONCLUSION
TL and OSL properties of five types of household salt commercially available in Romania have been
investigated. All samples displayed two main TL peaks at approximately 100
o
C and at either 300
o
C or 260
o
C,
when observing UV emission, and bright OSL signals under continuous stimulation with blue light. By
applying a standard multiple aliquot OSL (blue light stimulation, ultraviolet detection) procedure using a
stimulation temperature of 100
o
C subsequent to preheating for 10 s at 150
o
C, a linear dose response was
observed. Very encouraging values for the lower limit of detection have been estimated (less than 1 mGy for
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four samples). For these samples, signal loss was observed in the first 5 days after irradiation, but the
remaining signal maintained a stable level on further storage. The cause of this fading effect needs
supplementary investigation in order for correction procedures to be developed. Future studies should also be
focused on optimization of OSL and TL protocols, in order to fully use the potential of salt in retrospective
dosimetry applications. Nevertheless, the dosimetric properties of the OSL signals displayed upon irradiation
of different types of household salt presented in this study further confirm that this material should be
seriously considered as a potential retrospective dosemeter in the event of a radiation accident.
ACKNOWLEDGEMENTS
The authors are grateful to Professor Ann Wintle for proof- reading and making suggestions on an
early version of the manuscript. Dr. Daraban L. and C. Ivascu are thanked for providing the authors with
access to gamma irradiation facilities.
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FIGURE CAPTIONS
Figure 1. TL glow-curves (recorded to 400
o
C, heating rate of 5
o
C/s) for each salt type following an irradiation
with a dose of 400 mGy (
90
Sr-
90
Y). The three graphs plotted for each sample compare the immediate TL
output to the TL recorded following a preheat of 10 s to 150
o
C and the TL signal sampled after a one day
delay, with no preheating. Each glow curve has been recorded using a different aliquot.
Figure 2. Recorded OSL signal (stimulation temperature: 100
o
C; preheat treatment: 150
o
C for 10 s;
stimulation power: 12 mW/cm
2
) for salt type ‘B’ after an irradiation with 48 mGy (
60
Co) compared to the
background (natural) signal.
Figure 3. Pulse annealing curve for the OSL signal (measured at 100
o
C) for NaCl. Each data point represents
the average value obtained on four aliquots. All values are normalized to the output obtained following a 10 s
annealing at 150
o
C.
Figure 4. Mass normalized OSL dose response for salt type ‘B’ (each data point represents the average signal
obtained on six aliquots)
Figure 5. Effect of storage on OSL signals from 3 salt types (‘G’, ‘R’, ‘B’) investigated over a period of 29
weeks. The inset shows the signal loss observed for salt type ‘B’ over the first week. The values were
normalized with respect to the initial measurement data. The dose given was 48 mGy (
60
Co).
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Table 1. Origin and composition of the five types of table salt
Laboratory
code
Salt type Source Content
G iodized table rock salt
mine (exact source
unknown)
NaCl (≥97.5%), KIO
3
R
extra-refined iodized
table rock salt
Slanic Prahova salt mine,
Prahova county,
Romania
NaCl, KIO
3
, E 536
B
re-crystallized iodized
table rock salt
Cacica salt mine, Suceava
county,
Romania
NaCl, KIO
3
, E 536
S natural iodized sea salt
Greece
(Mediterranean Sea)
NaCl, Na
2
CO
3
, E 536
I salt substitute
Greece
(Mediterranean Sea)
NaCl(33.3%), KCl (66%),
E 504
Table 2. Summary of OSL specific luminescence and LLD (lower limit of detection). The determination
coefficient (R
2
) shows the goodness of fit obtained using a linear function.
Salt
type
R
2
OSL specific luminescence
(counts in 0.77 s /mg)/(mGy)
LLD
(mGy)
G 0.99 212 ± 16 0.66
R 0.99 340 ± 7 14
B 0.97 131 ± 8 0.04
S 0.99 165 ± 9 0.008
I 0.97 10 ± 1 0.21
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FIGURE 1
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FIGURE 2
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FIGURE 3
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FIGURE 4
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FIGURE 5
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Radiation Protection Dosimetry Submitted Manuscript
... The first group includes, Qattara Depression, Analytical NaCl and Siwa halite has three peaks (P1, P2 and P3) at average values 95°C-181°C-260°C, 98°C-189°C-270°C, and 97°C -182°C -270°, respectively, for the three samples P3 is the main peak and it may be considered as the dosimetric peak. The presence of the dosimetric peak at~266°C was reported for an Alpine salt with iodine (Ekendahl & Judas, 2010), two types of rock salt in Romanian (Timar-Gabor & Trandafir, 2013), and some of the domestic salts, from Australasia, Europe, Asia, and America (Hunter, . ...
... Many reviews for the storage time effect on TL response of household salt concluded that the loss of TL response may be~40% after 2 weeks and then remained stable (Elashmawy, 2018). Also, (Timar-Gabor & Trandafir, 2013) reported that there is rapid signal loss during first 7 days for some Romanian commercial salt after that the signal remained constant at~65% of its initial value over the period investigated (30 weeks). ...
Article
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Thermoluminescence (TL) sensitivity studied for some Egyptian halite (NaCl) samples. Three natural rock salts collected from Fayoum Governorate, Qattara Depression, and Siwa Oasis and two commercial salts (Table salt and Analytical NaCl) were studied for potential application to retrospective dosimetry. The chemical compositions of the samples were analyzed by using EDX technique. The Kinetic parameters were estimated by using peak shape method for general order. The deconvolution process for the glow curves was done using the peak fit program. The chemical analyses observe a difference in the trace impurities according to the collection area of the samples. All samples have three peaks (P1, P2, and P3) but the two peaks P2 and P3 suffered overlapping in case of table salt and Fayoum Governorate. The response curves are linear from, 10 up to 100 Gy for Table salt; Analytical salt and Siwa halite, in contrast, the dose–response curves for Qattara Depression and Fayoum halite are linear from 0.8 up to 100 Gy. The TL signal fading of the samples ranged from 21% to 34%, from the initial signal. The experimental results and the estimated kinetic parameters can be dedicating the ability to use the five investigated salt samples as a retrospective dosimetry.
... The calibration factor was calculated from the slope of dose linearity curve and its value was found to be 0.073 mGy/nC. By substituting all these values in equation 2 the MDD value for pink salt sample was found 0.475 mGy comparable to the values <1 mGy reported in the literature by Ekendahl et al., Timar-Gabor et al. and Benhardsson et al.[38,45,46] . ...
Article
In this study thermoluminescence characteristics of the pink Himalayan salt has been studied. For this purpose, pellets of pink Himalayan salt weighing 40 mg were prepared. The ICP-OES and EDX analytical techniques were used to find the elemental composition of the sample. It confirms the presence of Al, Mg, Ca, Sr, S, Zn, K, Mn and Fe etc. along with the main matrix. The XRD analysis shows that the salt has face centered cubic (FCC) structure with average crystallite size of 70.6 nm. The scanning electron microscope (SEM) was used for surface morphology. To investigate the thermoluminescence properties, the pellets were irradiated with ¹³⁷Cs source in the dose range of 1–5000 mGy. The glow curve indicated the presence of three peaks namely P1, P2 & P3 with two very prominent peaks occurring at 135 °C and 260 °C. The Tmax-Tstop procedure revealed the coinciding peaks in the glow curve and their relative positions. The trapping/kinetic parameters, such as electron trap depth (E), order of kinetic (b) and frequency factor (s) were explored by employing CGCD technique. The values of figures of merit (FOM) calculated at different doses (500 mGy, 1 Gy, 2 Gy & 5 Gy) were found to be 1.14%, 1.24%, 1.11% and 1.13% respectively. This indicates excellent agreement between the experimental and theoretical fitting. The post irradiation fading of the sample pellets were studied at dose of 500 mGy for different time intervals up to 8 week and 30% loss in TL signal was observed within first 24 h which becomes stable after 2 week. On the basis of these results it can be concluded that pink Himalayan salt has a potential to be used in radiation dosimetry.
... The early studies on luminescence properties of NaCl were systematized by McKeever (1985). Further research concerned the OSL of halite and common salts of various origins, which were widely investigated for dosimetric purposes (Bailey et al., 2000;Thomsen et al., 2002;Gartia et al., 2004;Zhang et al., 2005;Ankjaergaard et al., 2006;Murthy et al., 2006;Tanır et al., 2007;Bernhardsson et al., 2009, Khazal and Abul-Hail, 2010, Fujita et al., 2011Ekendahl and Judas, 2011;Polymeris et al., 2011;Spooner et al., 2011;Rodriguez-Lazcano et al., 2012;Christiansson et al., 2012;Spooner et al., 2012;Hunter et al., 2012;Mesterházy et al., 2012;Timar-Gabor and Trandafir, 2013;Christiansson et al., 2014;Druzhyna et al., 2016;Ademola, 2017;Biernacka et al., 2017;Singh et al., 2018;Elashmawy, 2018). Previous studies of the Polish halite showed its great potential for dosimetry due to a wide range of linear/superlinear OSL response to a radiation dose (OSL using green or infrared stimulation) . ...
Article
The complex kinetics of optically stimulated luminescence (OSL) in certain salts is associated with the effect of regeneration (RE). Until now, the RE effect was found in sodium and potassium chlorides (NaCl, KCl). The model of OSL kinetics explaining regeneration and fading was previously proposed in pure NaCl. However, it can be referred also to other materials. Verification of the model was performed based on the experimental results obtained for halite (rock salt mineral) and pure KCl crystals. Determination of the characteristic lifetimes of regeneration and fading was performed by adjusting the model solutions for a special case (without stimulation) to the data obtained from the VD-OSL method. In the case when stimulation is on during OSL readout, differential equations describing the model have no analytical solution. Therefore in order to model OSL decays the numerical simulations for various parameters were carried out. The obtained theoretical OSL decays are compatible with the measurement data.
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During recovery phases following a nuclear or radiological incident analyses of doses received by members of the public and responders are often required. Several methods have been investigated for use at different timescales after the incident, including assessments based on measurements of materials present at the time of the incident. Common salt has previously been shown to have potential for retrospective dosimetry in the mGy dose range using laboratory instrumentation. This preliminary study investigates the use of portable instruments, with unprepared commercially sourced salt, in dose ranges below 100 μGy. Responses from pulsed IRSL and portable OSL instruments were compared. For OSL measurements, detection limits of 7 μGy have been demonstrated, with detection limits of 30–340 μGy for the other instruments investigated. Dose responses in the 0–500 μGy range were determined for the most sensitive systems, which show a linear response over this dose range with a non-zero intercept representing doses received from environmental sources since manufacture of the salt. For use as a dosimeter, methods of removing or accounting for inherited signals will be required in this low dose range. The results demonstrate that salt has considerable potential for use in retrospective dosimetry below 100 μGy, and that measurements can be conducted with portable OSL instruments.
Article
Thermoluminescence (TL) and extended dosimetric characteristics of naturally occurring NaCl salt were studied. Pellets were prepared from mined crystalline salt obtained from Khewra salt mines, Pakistan and irradiated from 1 mGy to 10,000 mGy using Co‐60 gamma source. The TL response showed two dominant peaks around 125 °C and 230 °C respectively at low doses, with an additional peak in between at doses beyond 300 mGy. A linear and supra‐linear TL response was observed between 1 mGy‐100 mGy and 100 mGy‐10 Gy dose ranges respectively. During first 24 hours post irradiation, the TL intensity dropped by 20%. A maximum angular dependence of up to 50% was observed between 0 to 360°. For photon energies between 33 keV‐1.25 MeV significant energy dependence was observed for photons <100 keV only. Sample sensitivity increased with dose a qualitatively similar behaviour to TLD‐200. Zeff of the sample (14.6) was comparable to TLD‐200 (16.3). No significant dose rate effects (deviation for a Co‐60 source within 3.5%) on the TL sensitivity of the sample were found. The lowest detectable dose limit (LDDL) for salt sample was found to be 0.8 mGy whereas the sample reproducibility test showed a maximum of ±11% deviation from the first value.
Conference Paper
This brief overview of the use of household salt (NaCl) in optically stimulated luminescence (OSL) dosimetry is focusing on the use of NaCl pellets. It is suggested that the most optimal use of household NaCl, in general prospective dosimetry, is to compress the salt grains to pellets and read the radiation induced signal using OSL rather than TL. A summary of the main OSL dosimetric properties is provided for two Swedish household salts, and compared to the OSL properties of 100 different salts from all over the world
Article
Thermally and Optically Stimulated Luminescence (OSL) are known stimulated phenomena in condensed matter that can be used for luminescent material characterization. Both thermally and optically processes have become a successful practical tool in radiation dosimetry. Special attention is dedicated to bioceramic as a material of choice for many dosimetric applications. This paper reports experimental results of dysprosium trivalent ion doped lanthanum aluminate (LaAlO3:Dy³⁺) using thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL) techniques. Samples of LaAlO3:Dy³⁺ were irradiated to beta doses, in air, from 1.6 Gy up to 26 Gy and then were analyzed using both TL and OSL techniques to determine their luminescent properties. Nanostructured powders were confirmed by the X-ray diffraction technique. Luminescent phosphors show a thermoluminescent glow curve obtained being exposed beta radiation of two peaks: one located at around 160°C and the second one at 215°C. Meanwhile, OSL decay is exponential form. TL and OSL response as a function beta radiation dose was linear in the studied dose interval (from 1.6 Gy up to 26 Gy). The very good sensitivity and moderate fading will make this phosphor suitable for beta radiation detection, using both TL and OSL techniques.
Article
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In this study, the thermoluminescence characteristics of naturally occurring salt (NaCl) were assessed for the development of a radiation dosimeter. For this purpose, mined crystalline samples of salt were procured directly from Khewra salt mines in Pakistan. The samples were hand crushed, sieved, and compressed to pellets comparable in size to standard TLD chips, and irradiated to gamma radiation doses in the range of 5 mGy and 5000 mGy. Thermoluminescence (TL) response showed three main peaks in the glow curve around 115–130 °C, 150–170 °C, and 220–240 °C. A linear TL response was observed for the dose range of 5–100 mGy. The TL response became supra-linear for the dose ranges of 100–1000 mGy and 1000–5000 mGy. The Tm- Tstop method was applied to identify the overlapping peaks of the glow curve. Computerized glow curve deconvolution (CGCD) was then employed for the characterization of electron trap parameters such as frequency factor (s), activation energy (E), and the kinetic order (b), using General Order (GO) kinetics. The figure-of-merit (FOM) was found to be 1.08%, 0.94%, 0.77%, and 0.75%, at 500 mGy, 1 Gy, 2 Gy, and 5 Gy, respectively. The TL intensity faded by 20% within the first 24 h after irradiation and finally stabilized after two weeks. In addition, structural, morphological, and elemental analyses, were also performed using various analytical techniques. X-ray diffraction (XRD) showed that the salt crystallizes in a face-centered cubic structure. Scanning electron microscope (SEM) micrographs indicated that the crystallites are closely packed and cubic-shaped with non-uniform size, and mostly found in the agglomerated form. Similarly, the elemental analysis confirmed the presence of impurities such as Mg, Sr, S, K, O, and Ca, in the samples. The present study concludes that the pellets made from salt samples from Khewra mines have a potential for use as radiation dosimeters.
Article
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The pure and Ce3+-doped NaCl crystals were grown using the resistance heating Czochralski method. The structural, mechanical, and optical properties of the grown crystal were investigated by X-ray diffraction (XRD), micro-hardness, optical absorption, photoluminescence (PL), PL excitation (PLE) spectroscopy, and decay time measurement. The XRD data indicated that the NaCl host lattice was compressed when Ce atoms were incorporated and the peaks shifted to the large angle side. The ICP-AES and XPS analyses verified that Ce3+ is the dominant state of cerium in NaCl crystal. The hardness of the NaCl:Ce3+ crystal was larger than that of pure NaCl crystal and it was anisotropic. Optical absorption confirmed that the three states of 5d level splitting of Ce correspond to the absorption peaks of 202, 215, and 227 nm. The intense emissions located at 342 and 356 nm were attributed to the radiation transitions 5d → 2F5/2 and 5d → 2F7/2 in Ce3+, respectively. The energy-level scheme for the Ce3+ ion in the NaCl crystal was proposed from the PL and PLE analysis. The luminescence decay time of NaCl:Ce3+ crystal is 38.57 ± 0.16 ns. These observations indicate that the NaCl:Ce3+ crystal should be a promising material for use in radiation dosimetry and scintillation applications.
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Thermoluminescence (TL) response of ten Indian brands of iodized salt has been recorded for possible use in TL dosimetry. It has been observed that a heat treatment of one minute at 500°C reduces the complexity of the glow curve pattern. Further, in many cases heat treated samples exhibit intense peaks at higher temperature which are stable at room temperature (25°C) whereas some brands like Sungold, Tata, Ankur and Dandi inhibit such peaks. TL response of two such cases namely the integration zone 200-400°C of the glow curve of Taja and Shudh brands of iodized salt follow polynomial of degree three to beta exposure in the dose range 1 to ≃ 25 Gy; indicating its potentiality in TL dosimetry.
Article
The alkali halide NaCl (Common salt) is an environmentally-abundant phosphor of considerable potential for retrospective dosimetry and radiological event analysis due to its high sensitivity to ionising radiation when analysed by Thermoluminescence (TL), Optically-stimulated luminescence (OSL) or Infrared-stimulated luminescence (IRSL). We report here aspects of luminescence from NaCl relevant to the development of valid protocols for measurement of recent ionising radiation exposure. The timescale of interest in this application is from days to decades, hence our emphasis is on detection and characterisation of TL emission in the 100–300 °C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 °C). A collection of 19 salt samples was assembled, including samples of rock salt and domestic salt produced by evaporation from brine. Analysis of TL emission spectral changes, together with previously reported TL, OSL and IRSL sensitivity changes, confirmed activation of sensitivity change by exposure to temperatures exceeding 160 °C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 × 1011 s−1 for the 100 °C TL peak, giving a lifetime at 20 °C consistent with previous calculations and in the range of 7–14 h.
Article
The thermoluminescence (TL) from common salt (NaCl) is investigated to determine its suitability as an opportunistic retrospective dosimeter. In this study the TL is analysed from a wide range of domestic salts, sourced from Australasia, Europe, Asia and America. The emission spectra for pre-existing or “Natural” TL (NTL) and laboratory-irradiated “Artificial” TL (ATL) were analysed using a Fourier Transform spectrometer, giving luminescence intensity as a function of temperature and photon energy. Fading behaviour in the candidate TL emission peaks, observed at 200–260 °C under the measurement conditions used, was investigated at various storage temperatures and storage intervals between irradiation and read-out. This included TL emission spectral measurements at storage intervals ranging from minutes to months. Nearly all samples showed strong ATL emission at 590 nm, with much weaker emission from the commonly measured UV-blue region. NTL was very small or undetected for most samples. The storage tests showed that the TL in the 260 °C region is relatively stable and we conclude that TL from NaCl possesses suitable dose sensitivity and stability for use as an opportunistic retrospective dosimeter.
Article
The luminescence properties of synthetic alkali halides in general and different doped synthetic sodium chloride (NaCl) in particular have been widely studied. However, the spectral emission of natural NaCl has been scarcely reported. Accordingly, this work reports on the thermoluminescence (TL), infrared stimulated luminescence (IRSL) and radioluminescence (RL) response of the well-characterized natural NaCl (by means of X-ray fluorescence and differential thermal and thermogravimetric techniques) in the range of 200–800nm. As observed in the 3D-TL plots, the main emission of the irradiated samples appears in the UV-blue region and can be deconvoluted into four groups of components (at 70, 180, 220 and 315°C) assuming first order kinetics. The non-irradiated samples exhibited a negligible luminescence signal. The RL response reveals the appearance of five bands peaked at 290, 370, 430, 500 and 620nm. The IRSL spectral emission shows a low intensity broad band with non-well defined peaks.
Article
We have measured the thermoluminescence of a number of NaCl and KCl crystals following irradiation at ambient temperature with the same dose (10 kGy) of Co-60 γ rays. We compare the TL of pure samples and of samples doped with europium and calcium ions. In the case of NaCl, additional impurities (Ni, Pb, Sr and Cr) have been investigated. The effects of irradiation are determined using optical absorption and thermoluminescence. Factors investigated include the effects of different dopants on TL glow curves and the effects of thermal annealing samples at 400 °C before the irradiation. Changes in TL glow curves relating to changes in the state of aggregation of the impurities produced by pre-irradiation annealing are reported in this paper. Perhaps the most significant effect is a temperature shift of the main glow peak in pre-annealed compared to not pre-annealed samples in the case of Eu doped NaCl. The magnitude of the shift depends on the concentration of the Eu dopant. Shifts are also observed for Ni and Sr impurities in NaCl, but not for Ca and Cr impurities in NaCl. In the case of KCl, glow peaks generally occur at similar temperatures in doped samples and do not shift when doped samples are pre-annealed. Here the main effect of different impurities is to influence the size of the emission and not the structure of the glow curve. Results are discussed in terms of current theories of thermoluminescence.
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Dose evaluation procedures based on luminescence techniques were applied to 50 quartz samples extracted from bricks that had been obtained from populated or partly populated settlements in Russia and Ukraine downwind of the Chernobyl NPP. Determinations of accrued dose in the range ∼30–300 mGy were obtained using TL (210°C TL and pre-dose) and OSL (single and multiple aliquot) procedures. Overall, good inter-laboratory concordance of dose evaluations was achieved, with a variance (1σ) of ∼±10 mGy for the samples examined.
Article
McKeever gives us a comprehensive survey of thermoluminescence, an important, versatile, and widely-used experimental technique. Bringing together previously isolated specialized approaches, he stresses the importance of the solid state aspects of the phenomenon and links these to applications in dating, dosimetry, and geology.The book contains chapters on analysis and special properties, on instrumentation, and on the variety of defect reaction--using the alkali halides and SiO2 as examples--that can take place within a material to yield thermoluminescence. Three chapters concerning applications discuss the features of the solid state reactions to explain some of the properties observed in practice.
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Experimental work on the electron energy-band structures of the alkali halides is reviewed in order to obtain a set of basic parameters (band gap Eg, threshold energy Et, and electron affinity χ) that are used subsequently (paper II) to assess the merits of various theoretical band calculations. Included is a summary of our recent ultraviolet photoelectron spectroscopic studies of the alkali halides. Various experimental and interpretational difficulties are discussed and a number of systematic trends delineated.