Determination of dosimetric properties of MgO doped natural amethyst samples

Applied Radiation and Isotopes 116 (2016) 150–156

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Determination of dosimetric properties of MgO doped natural amethyst samples N. Nur a, V. Guckan b, N. Kizilkaya c, T. Depci c,n, C. Ahmedova d, A. Yucel c, A. Ozdemir b, V. Altunal b, V. Koc e, Z. Yegingil b a

Adiyaman University, Electrical Electronic Engineering, 02040 Adiyaman, Turkey Cukurova University, Physics Department, Balcali, Saricam, 01330 Adana, Turkey c Inonu University, Mining Engineering Department, 44280 Malatya, Turkey d Adiyaman University, Chemical Department, 02040 Adiyaman, Turkey e Adiyaman University, Vocational School, Department of Metal Tech., 02040 Adiyaman, Turkey b

H I G H L I G H T S







Magnesium was doped into natural amethyst quartz sample (NA). The chemical structures of the undoped and MgO doped NA were identified and compare with each other. The main dosimetric properties of MgO doped NA were investigated. MgO doped NA as a phosphor might be used in many fields concerning with the dose range from 0.1 Gy up to 100 Gy.

art ic l e i nf o

a b s t r a c t

Article history: Received 21 May 2016 Received in revised form 2 August 2016 Accepted 5 August 2016 Available online 6 August 2016

In this paper, the thermoluminescence (TL) dosimetric characteristics of MgO doped natural amethyst samples (Mg-NA) are presented. The morphologies and chemical structures of the powder form samples were identified using XRD, FTIR, SEM, SEM mapping and EDX. Comparison of the TL intensities showed that 10 wt% Mg-NA was nearly 150 times more sensitive than undoped amethyst and the main dosimetric properties proved that 10 wt% Mg-NA may be a promising phosphor for clinical and radiotherapy purposes. & 2016 Elsevier Ltd. All rights reserved.

Keywords: MgO Natural amethyst quartz Sensitivity change Pre-dose sensitization

1. Introduction Natural materials have great attention in the dosimetric application since most of them have excellent luminescence properties. Amethyst quartz is one of the most famous natural materials and extensive researches have been done regarding its thermoluminescence (TL) properties for dosimetric applications. Depending on the ore deposition type, natural amethyst quartz contains various type of minerals which affect the TL properties (Adamiec, 2005; Aitken, 1998; Correcher et al., 1998; Preusser et al., 2009; Rocha et al., 2003; Toktamis et al., 2007; Topaksu et al., 2013). For example, Zhang et al. (1994) investigated the thermoluminescence spectra of quartz and natural amethyst n

Corresponding author. E-mail address: [email protected] (T. Depci).

http://dx.doi.org/10.1016/j.apradiso.2016.08.005 0969-8043/& 2016 Elsevier Ltd. All rights reserved.

quartz which have an emission bands at 250–800 nm and 740– 750 nm, respectively. They explained the difference between the emission bands by variation of the iron ion impurity concentration in the structure. Recently, TL properties of seven Brazilian natural quartzes, named the blue, the green, the red, the pink, the black, the sulfurous and the milky quartz, have been investigated by Farias and Watanabe (2012). All samples were irradiated by X- and gamma radiation beams and their TL glow curves, energy response, dose response and reproducibility were investigated and compared with each other. The results indicate the variation on TL properties of the natural quartz samples and the authors identify the difference with the amount of aluminum concentration in the natural quartz. Over the last decade, researches have been focused on metal oxide doping process to improve and investigate the TL properties of quartz and natural amethyst. Natural amethyst samples have

N. Nur et al. / Applied Radiation and Isotopes 116 (2016) 150–156

2. Materials and methods Natural amethyst quartz samples as a crystal form were collected from Dursunbey, Balıkesir, Turkey. The MgO was doped into the natural amethyst sample by high temperature solid state method. The natural amethyst samples were ground using Retsch PM 100 planetary ball mill and sieved with 45 mm size sieve. Then, 1 g of the natural amethyst sample ( 45 mm size) and 0.1 g MgO (10 pct wt) were weighted and put into a porcelain crucible. The crucible was heated at 1100 °C for 8 h to finalize the doping procedure. The same doping procedure was also followed using different amounts (0.01 wt%, 1 wt%, 5 wt%, 12.5 wt% ) of MgO. In addition, the undoped natural amethyst samples were heated at 1100 °C for 8 h to compare the TL properties of undoped and MgO doped natural amethyst sample, confirming that whether the observed behavior is characteristic of the MgO doped natural amethyst sample or the original (natural) sample depending on the doping temperature. Phase compositions and crystallinity of the samples were analyzed by X-ray powder diffraction and the patterns were recorded using Rigaku Miniflex 600 with Cu Kα (40 kV, 15 mA, λ ¼1.54050 Å). The vibrational modes of functional groups of the samples by Perkin Elmer Spectrum One FTIR and IR bands of undoped and MgO doped amethyst were compared with each other and the literature data. The morphology as well as the chemical structure were investigated with SEM images, mapping and EDX analysis using LeO EVO 40 scanning electron microscope. All TL readouts have been performed with a Riso TL/OSL reader DA20 model. The irradiation unit assembled in the system is a 90 Sr/90Y beta source has an activity of 1.48 GBq (40 mCi), which emits beta particles with a maximum energy of 2.27 MeV. The dose rate of the source is about 6.689 Gy/min which gives an amount of dose of 0.11 Gy/s to quartz at the sample location. 10 mg powder samples handled in bordered discs and TL read outs were performed in nitrogen atmosphere from room temperature up to 450 °C with 3 °C/s heating rate. In the all experiments except for the reusability text, at least three fresh samples (multiple aliquots) were used to prevent the mistake on the sensitivity depending on inhomogeneities.

Intensity (a. u.)

Mg-NA

U-NA 5

15

25

35 45 2 θ (Degree)

55

65

Fig. 1. XRD patterns of undoped (U-NA) and 10% wt Mg-doped natural amethyst (Mg-NA).

all intense reflections match with the powder diffraction data of quartz which is reported in ICDD Card no: 01-078-2315 and the cell parameters of the samples were calculated as follows: a¼ b¼ 4.915 Å and c ¼5.407 Å. The patterns of the undoped and MgO doped natural amethyst showed great similarity with each other and no reflections were recorded associated with MgO activator, as expected. The infrared spectra of undoped and 10 wt% MgO doped natural amethyst are presented in Fig. 2. By comparing the band positions and IR spectra of the samples, the vibrations did not change and no new bands were recorded depending on the dopant and doping procedure, meaning that MgO as a dopant did not cause any significant change in the host structure. This finding supported the XRD results. All IR bands confirm the quartz structure which has the specific wavenumbers at 796 cm  1 and 1087 cm  1, describing the stretching vibration of Si–O, at 660 cm  1, attributing to the Si–O–Si bending vibrations and O–Si–O deformation vibration (Vidyadhar and Rao, 2007). SEM image are presented in Fig. 3, showing the non-uniform and irregular shaped particles, some agglomeration and vitreous form of the structure. In detailed analysis of SEM images using mapping options indicated that the main structure of the natural amethyst consists of Si and O as expected. In addition, Mg was also identified in the main structure. MgO content in the host structure was determined as 9.93 wt% by EDX. According to SEM images (Fig. 3), the morphology and the particle size of the sample are not homogenous as expected. In the beginning of this study, consistencies of the TL intensity and the

Mg-NA Transmitance (a. u.)

been doped some activators such as copper, cobalt, lithium, aluminum to investigate color center and luminescence properties (Nur et al., 2015; Song et al., 2010; Barve et al., 2012; 2016; GomezRos et al., 2002; Fernando et al., 2009). Comparison of the luminescence studies show that the sensitivity of metal oxide doped amethyst is higher than the natural one, but fading is a main and common problem and the obtained main peaks fade in a very short time. Keeping this in view, in the present study, for the first time, different amounts of MgO were doped into the powder form of natural amethyst quartz samples to investigate the TL dosimetric properties and their usability for dosimetric applications. The glow curve structure, dose response, reusability, sensitivity, superlinearity and fading properties were investigated in detail and the findings reported below indicate that the 10 wt% MgO doped natural amethyst quartz (with effective atomic number Zeff ¼11,56) may be a promising phosphor for clinical and radiotherapy purposes.

151

U-NA

3. Results and discussion 3800

3.1. Characterization of undoped and Mg doped natural amethyst The powder XRD pattern of undoped (U-NA) and 10 wt% MgO doped natural amethyst (Mg-NA) are given in Fig. 1, indicating that

3400

3000

2600

2200

1800

1400

1000

600

-1

Wavenumber (cm ) Fig. 2. IR spectrum of undoped (U-NA) and 10% wt Mg-doped natural amethyst (Mg-NA).

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U-NA

Mapping of Mg-NA

Si content in Mg-NA

Mg-NA

Mg content in Mg-NA

O content in Mg-NA

Fig. 3. SEM images of U-NA and Mg-NA and the mapping of Mg-NA (Mg: blue color, Si: red color, O: green color). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

glow curve structure between the samples were checked using four Mg-NA samples which were irradiated at the same condition. No any big differences on TL intensity and the glow curve structure were recorded (figure was not given in the text) and the standard deviation for the TL intensity obtained at 210 °C was found as approximately 5%. It meant that inhomogeneity of particle size below 45 mm could not seriously affect individual measurements.

3.2. Glow curve structure The natural amethyst quartz samples have specific numbers of TL peaks in the range of 100 °C and 450 °C depending on impurities in the structure (Toktamis et al., 2007; Adamiec, 2005; Rocha et al., 2003; McKeever, 1985). Fig. 4 and Fig. 5 show the TL glow curves of undoped natural amethyst quartz (U-NA) and MgO

N. Nur et al. / Applied Radiation and Isotopes 116 (2016) 150–156

3.0

10 Gy 125 0C

1.0x105

150 0C

5.0x104

210 0C

0

280 C

2.5

Normalized peak height

TL emission (a.u.)

U-NA

100 0C

1.5x105

345 0C

2.0 1.5 1.0 0.5 0.0

0.0 100

200

300

400

0.01%

Temperature (0C)

1%

5%

10%

12.5%

MgO concentrations

Fig. 4. TL glow curve of U-NA recorded after irradiation with 10 Gy dose for heating rate of 3 °C/s.

10 Gy

2.0x105

TL emission (a.u.)

1.5x105 120 0C 145 0C

1.0x105

1.2x10

Mg-NA 10 Gy

95 0C

TL emission (a.u.)

153

210 0C

9.0x10

6.0x10

3.0x10

4

5.0x10

10% MgO doped NA Undoped NA

0

280 C

330 0C

0.0 100

0.0 100

200

300

400

Temperature (oC) Fig. 5. TL glow curve of Mg-NA recorded after irradiation with 10 Gy dose for heating rate of 3 °C/s.

doped natural amethyst quartz sample (Mg-NA), respectively. The glow curve of the natural quartz had 6 distinguishable peaks at 100 °C, 125 °C, 150 °C, 210 °C, 280 °C and 345 °C after irradiation of the sample with 10 Gy of beta exposure for 3 °C heating rate. The glow curve structure of Mg-NA sample showed great similarity with that of U-NA and its peak temperatures were detected as 95 °C, 120 °C, 145 °C, 210 °C, 280 °C and 330 °C (Fig. 5). A comparison of the TL glow curves showed no noticeable difference between the two samples of observations, just the peak temperatures slightly changed, indicating that MgO did not interact with an intrinsic defect. The increments in the TL intensity are related to the luminescence centers not with the electron traps (Nur et al., 2015; Depci et al., 2008; Morris and McKeever, 1994). TL glow curve structures for the different dose levels (5 Gy and 50 Gy) were also analyzed (figure not given in the text) and the shape of the TL glow curves showed great similarity with each other, indicating a dose levels-independent character. Our preliminary investigation showed that the peak temperature lower than 150 °C was abruptly faded, so the Mg-NA samples were preheated at 150 °C for 10 s to isolate peaks which were detected below 150 °C. After this process, the peak at 210 °C was chosen as a main peak and evaluated for dosimetric application. In this study, the TL glow curves of the natural amethyst samples doped with different concentrations (0.01%, 1%, 5%, 10% and 12.5%) of MgO were also obtained and the maximum peak

200

300

400

Temperature ( C) Fig. 6. Normalized peak heights of 210 °C peak obtained from TL glow curves of Mg-NA samples doped with different concentrations (0.01, 1, 5, 10% and 12.5%) (a) and the TL glow curves of U-NA and 10 wt% Mg-NA (b) after 10 Gy of beta irradiation. The preheating procedure of 150 °C for 10 s was applied during the readouts.

heights of the main dosimetric peak (at around 210 °C) were normalized and represented in Fig. 6a. As seen that, the highest TL intensity was obtained from 10 wt% MgO doped natural amethyst and after this ratio (e.g. 12.5 wt%), the TL intensity of the dosimetric peak drastically decreased and the main structure started to decompose (not given in the text). This phenomena is observed in the literature and called as quenching effect (Souza et al., 2014; Depci et al., 2008; McKeever, 1985). Therefore, in the present study, the main dosimetric properties of 10% wt Mg doped natural amethyst quartz sample were investigated. Undoped and 10% wt MgO doped natural amethyst samples were irradiated with 10 Gy of beta dose and TL glow curves were recorded immediately after irradiation using the preheating procedure described above (Fig. 6b). The comparison of height of the main glow peaks (at around 210 °C) showed that TL sensitivity of the 10% wt MgO doped natural amethyst was approximately eight times higher than that of the undoped natural amethyst samples. In the present study, The TL sensitivity of the 10 wt% Mg-NA was also compared with that of TLD-100. The TL sensitivity is expressed as peak height of the glow curves corrected for per unit of mass of dosimeter and the data are given in relation to the TL sensitivity of TLD-100. Comparison studies indicated that TL sensitivity of TLD-100 was approximately 7 times higher than that of Mg-NA.

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3.3. The pre-dose sensitization

3.0 5 Gy

3.4. Reusability One of the most important factors for dosimetric materials is reusability property. The TL sensitivity of phosphors may be changed and adversely affected after repeatedly usage, since the electrons might be trapped and accumulated into deep trap after each treatment causing the non-constant TL sensitivity over the usage time (Chen and McKeever, 1997). Therefore, the reusability property of the 10 wt% Mg-NA sample was investigated and the experiments were repeated 11 times. After each cycle, the sample was irradiated and then the glow curve was recorded. The obtained glow peaks were normalized to first readout using the area under the glow curve. In addition, the Mg-NA samples were

Before High Dose After High Dose 10 Gy of test dose

8x105

TL emission (a.u.)

~19 fold increase 6x105

4x105

2x105

x2

0 100

200

300

400

Unsensitized MgO doped amethyst

2.5

Normalized total counts

Literature survey shows that TL sensitivity of quartz can be changed after the high dose level irradiation followed by annealing procedure. The pre-dose radiation application enhances the TL sensitivity, considering in dosimetric application (Nur et al., 2015; Souza et al., 2014; Topaksu et al., 2013; Chen and McKeever, 1997; Polymeris et al., 2012). Therefore, in the present study, the effect of pre-dose application of 10% wt Mg-doped natural amethyst was investigated. The 10 wt% Mg-NA samples were irradiated with 10 Gy dose and then the samples were pre-heated at 150 °C for 10 s and the TL glow curves were recorded (first readout). After that, they were exposed by various dose levels (0.5, 1 and 2 kGy) to sensitize the samples. The trapped electrons occurred with the high dose irradiation was emptied by annealing procedure (450 °C for 1 h). Afterwards, the dose of 10 Gy was used and the TL glow curve was recorded (second readout). Comparing the first and the second readout, the results indicated that the TL intensities of 210 °C peak increased with increasing the pre-dose values and the highest TL intensity was obtained for 2 kGy of high dose (19 fold increases). Therefore, the effect of pre-dose of 2 kGy beta irradiation on the TL intensity of Mg-NA is presented in Fig. 7. The pre-dose application enhanced 19 times of the TL sensitivity due to the probability of photon emission per thermally released charge, showing that the number of activated luminescence centers participating in the TL emission was increased (Nur et al., 2015; Topaksu et al., 2013; Chen and McKeever, 1997; Polymeris et al., 2012). This result indicated that the pre-dose application should be taken into consideration in order to improve TL sensitivity.

2.0

137%

1.5

1.0

0.5

0.0

1

2

3

4

5

6

7

8

9

10

11

12

Cycle numbers Fig. 8. Reusability of unsensitized Mg-NA samples for 11 cycles. TL glow curve recorded immediately after irradiated the samples with 5 Gy of beta dose.

divided into two groups. The samples in the first group were irradiated with 5 Gy of test dose and the TL glow curve was recorded. This procedure was repeated for 11 times. The obtained results are given in Fig. 8, showing that the TL sensitivity of the peak at 210 °C increased 137% at the end of the 11 repeated cycles. This shows new traps occurred depending on the radiation exposure at each cycle (Nur et al., 2015; Topaksu et al., 2013; Toktamis et al., 2007; Chen and McKeever, 1997). The samples in the second group were sensitized by pre-dose procedure. These sensitized samples were exposed by 5 Gy and 50 Gy of the test dose and then, the TL glow curves were recorded after each cycle (11 times) to examine their reusability properties. The variation of the TL intensities of the peak at 210 °C were given in Fig. 9. The TL sensitivity of the sensitized samples decreased 10% for 5 Gy and 13% for 50 Gy of the test dose. 3.5. Dose response Dose response of phosphors should be known to determine the linearity range which is very important for dosimetric applications and ideal phosphors having linear curve for all dose range are preferred. However, lots of dosimetric materials show different non-linear effects depending on a chemical composition of host material, dopants type and dopant concentration. In the literature, TL glow curves of natural quartz samples show three different kind of dose response, linearity (up to about 100 Gy), stationary (in the range of 100–400 Gy) and a rapid increased about 400 Gy due to the oxygen vacancies (Watanabe et al., 1998; Toyoda and Ikeya, 1991; Chawla and Singhvi, 1962). In order to examine the dose response property of the 10 wt% Mg-NA samples, the different dose levels in the range of 0.1 Gy up to 100 Gy were applied. For each dose levels, three fresh sensitized samples were used and the average values of TL intensities at 210 °C peak were taken and standard deviations were calculated. The results are given in Fig. 10, showing the linear dose response curve between 0.1 Gy up to 100 Gy. The superlinearity index g(D) was calculated as 0.98 which is very close to 1, indicating the linearity (Chen and McKeever, 1997). This is a good agreement with the literature data (Nur et al., 2015; Topaksu et al., 2013; Polymeris et al., 2012; Rossman, 1994).

0

Temperature ( C) Fig. 7. The sensitivity change after the high dose application. The test dose applied was 10 Gy and 2 kGy beta.

3.6. Fading It is generally expected that the count of trapped electrons in a

N. Nur et al. / Applied Radiation and Isotopes 116 (2016) 150–156

5 Gy Sensitized MgO doped amethyst

20 Gy dose 1.5x105

TL emission (a.u.)

Normalized total counts

1.4

1.2

1.0

0.8

-7%

-10%

155

0 hour 6 hours 24 hours 1 week 2 weeks 3 weeks 4 weeks

1.0x105

5.0x104

0.6 0.0

1

2

3

5

4

6

7

8

9

10

11

100

12

1.0

0.8

-13% 0.6 3

5

4

6

7

8

9

10

11

12

Cycle numbers Fig. 9. Reusability of 10% wt. Mg-doped natural amethyst sample for 11 cycles (5 Gy (a) and 50 Gy (b) of beta dose).

Equation

Integrated peak area (a.u.)

109

y = a + b*x

Instrumental Weight Residual 7.15051 Sum of Squares 0.99959 Pearson's r 0.99909 Adj. R-Squar Value

108

Intercept Slope

B

et al., 2015; Topaksu et al., 2013). The fifteen 10 wt% Mg-NA fresh samples were irradiated by 20 Gy beta dose and the samples were divided in five groups. Each group was stored in dark and dry room at 25 °C. The fading characteristics were determined over a period of four weeks. The change of the TL glow curves depending on the storage time are given in Fig. 11, indicating that the intensity at low temperature peak (around 95 °C) was intensively disappeared in room temperature. On the other hand, the peak at 150 °C was not completely faded. The TL intensity decreased of 70% at the end of the 4 weeks. To examine the variation of the TL intensity of 210 °C peak, the normalized intensity values with the standard deviations are given in Fig. 12. It can be seen that the TL intensity of the main peak just faded 1% at the end of the 4 weeks. On the other hand, abnormal fading characteristics were observed at 2 weeks and then turn back to normal range. The TL intensity was increased of 21%, suggesting that electrons which were located into deep traps passed to shallow traps (Spurny and Kvasnika, 1974).

Standard Err

7.0347 0.9795

0.01039 0.00988

(b) 10

Mg-NA

1.4

210 C peak after 20 Gy dose

7

MgO doped amethyst y=a+b*x 106 0.1

1

10

100

Dose (Gy) Fig. 10. Dose response curve of 10% wt. Mg-doped natural amethyst sample using the integrated peak area centered around 210 °C (dose range between 0.1 Gy and 100 Gy).

host matrix should not be changed depending on storage condition and duration time. If it changes, this situation is called as fading. TL signal should be stable at ambient room temperature in a storage time to supply the compatibility between the light emitted resultant and the dose exposed (Toktamis et al., 2007; Nur

Peak height (a.u.)

Normalized total counts

Fig. 11. TL glow curves of 10% wt. Mg-doped natural amethyst sample after different storage time intervals at room temperature after irradiated by 20 Gy of beta dose.

1.2

2

400

Temperature ( C)

50 Gy Sensitized MgO doped amethyst

1

300 0

Cycle numbers

1.4

200

1.2

21%

1.0

-1% 0.8

0.6

0

1

2

3

4

Time (weeks) Fig. 12. Normalized peak height for the main selected peak at 210 °C after different storage period for 20 Gy of beta dose.

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4. Conclusion This paper describes the dosimetric properties of the MgO doped natural amethyst quartz sample collected from Dursunbey, Balikesir (Turkey). The characterization studies showed that the dopant concentration and procedure did not cause any change into the host structure. The TL studies of undoped natural amethyst and MgO doped natural amethyst samples indicated similar glow curve structures. The 10 wt% MgO doped amethyst have 6 distinguishable TL glow peaks at 95 °C, 120 °C, 145 °C, 210 °C, 280 °C and 330 °C. Their comparative TL studies showed that 10 wt% MgO doped amethyst was nearly 150 times more sensitive than undoped amethyst. After 11 repeated cycles, TL sensitivity decreased 13% in the recorded high dose application. The beta-dose response of the selected main peak at 210 °C had linear curve between the dose range of 0.1 Gy up to 100 Gy and the superlinearity index g(D) was calculated as 0.98. The overall results indicate that 10 wt% MgO doped natural amethyst sample is a promising phosphor and might be used concerning with the dose range from 0.1 Gy up to 100 Gy for dosimeter application.

Acknowledgment This project has been supported by NATO in the frame of the NATO Science for Peace and Security (SPS) Programme (Belgium) under the project number SfP984649 and by Cukurova University under the project number FEF-2014YL3. The authors also would like to thank Adiyaman University Rectorate (Project no AMYOBAP/2014-0004) and Inonu University (Project number: 2015/54) for their financial support.

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