LM-OSL thermal activation curves of quartz: Relevance to the thermal activation of the 110 °C TL glow-peak

LM-OSL thermal activation curves of quartz: Relevance to the thermal activation of the 110 °C TL glow-peak

Radiation Measurements 43 (2008) 263 – 268 www.elsevier.com/locate/radmeas LM-OSL thermal activation curves of quartz: Relevance to the thermal activ...

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Radiation Measurements 43 (2008) 263 – 268 www.elsevier.com/locate/radmeas

LM-OSL thermal activation curves of quartz: Relevance to the thermal activation of the 110 ◦C TL glow-peak N.G. Kiyak a,∗ , G.S. Polymeris b,c , G. Kitis c a Physics Department, Faculty of Science and Arts, ISIK University, Istanbul, Turkey b Archaeometry Laboratory, Cultural and Educational Technology Institute, R.C. “Athena”, Tsimiski 58, 67100 Xanthi, Greece c Nuclear Physics Laboratory, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

Abstract The thermally activated characteristics (TAC) of the linearly modulated optically stimulated luminescence (LM-OSL) signals of seven quartz samples from different origin were studied relative to the TAC of their respective thermoluminescence (TL) glow-peaks at 110 ◦ C. Within the framework of the study the TAC behavior of the LM-OSL was investigated by measuring the OSL signal at room temperature (RT) with the 110 ◦ C glow-peak present during OSL measurements, as well as, at 125 ◦ C without the glow-peak at 110 ◦ C removed by a cut-heat at 180 ◦ C prior to OSL measurement. The LM-OSL curves were analyzed into individual components using a computerized deconvolution procedure. It was found that all individual LM-OSL components of each kind of quartz follow the TAC behavior of the respective TL glow-peak at 110 ◦ C. The fourth component of the LM-OSL curve, centered at about tm = 400 s, appeared when the OSL measurements were performed at RT, whereas it was absent when the OSL measurement were performed at 180 ◦ C. It is suggested that this component is closely related with the TL glow-peak at 110 ◦ C. © 2007 Elsevier Ltd. All rights reserved. Keywords: Thermally activated characteristics (TAC); Thermoluminescence (TL); Quartz; Deconvolution

1. Introduction The thermoluminescence (TL) sensitivity of the 110 ◦ C glowpeak in quartz samples is known to depend on the irradiation and heating treatment of the samples. The plot of the sensitivity to a small beta dose versus the pre-annealing temperature gives rise to the well-known thermally activated curve (TAC). TACs are usually obtained by using either a single aliquot procedure (SA-TAC), or by using different aliquots for each activation–irradiation–readout cycle in a multiple aliquot procedure (MA-TAC). The exact shape of the TAC depends on the type of the quartz sample studied, as well as on its thermal and radiation history. However, the general features of a TAC include a steep rise in sensitivity to a maximum value, usually located between 450 and 600 ◦ C, followed in some cases by a decrease of the monitored sensitivity, known as thermal deactivation ∗ Corresponding author. Tel.: +90 212 5287182; fax: +90 212 5287160.

E-mail address: [email protected] (N.G. Kiyak). 1350-4487/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2007.12.039

(Bailiff, 1994). This is a common behavior of TAC in many quartz samples. Aitken and Smith (1988) suggested that changes in the sensitivity of the 110 ◦ C TL glow-peak signal and the OSL signal might be attributed to a common mechanism. The very interesting relationship between the 110 ◦ C TL and the OSL sensitivity has been extensively studied (Murray and Roberts, 1998; Wintle and Murray, 1998; Chen et al., 2000; Koul and Chougaonkar, 2007). The present work is an investigation of whether the linearly modulated optically stimulated luminescence (LM-OSL) also exhibits a similar TAC behavior. The aim is twofold: (a) to investigate whether the TL at 110 ◦ C signal can act as a normalization factor to any of the LM-OSL components and (b) to investigate relation of the TL glow-peak at 110 ◦ C with the fourth component of the LM-OSL curve which appears only when LM-OSL measurement is performed at room temperature (RT). The reason is to examine if all properties and applications of the TL 110 ◦ C glow-peak can be extrapolated to an individual LM-OSL component.

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2. Experimental procedure The TAC study was performed on five quartz samples originated from Turkey (Altınkum, Sile, ¸ Ataköy, Pendik, Table 1 The measurement protocols used in the study Step

Treatment

Protocol A: room temperature measurements protocol 1 Irradiation with a test dose of 8.5 Gy 2 LM-OSL for 1200 s at 25 ◦ C 3 TL readout up to the first activation temperature 250 ◦ C at 1 ◦ C/s 4 Irradiation with test dose of 8.5 Gy 5 LM-OSL for 1200 s at 25 ◦ C to obtain the activated LM-OSL

3. Method of analysis The original first order kinetics equation proposed by Bulur (1996) was transformed by Polymeris et al. (2006), so that instead of the parameters n0 and , to contain the parameters Im and tm which are obtained directly from the experimental curves. The transformed form is

Steps 3–5 are repeated for the same sample by increasing the activation temperature in steps of 10 ◦ C up to 500 ◦ C Protocol B: high temperature measurements protocol 1 Irradiation with a test dose of 8.5 Gy 2 Cut-heat TL to 180 ◦ C 3 LM-OSL for 1200 s at 125 ◦ C 4 TL readout up to the first activation temperature 250 ◦ C at 1 ◦ C/s 5 Irradiation with test dose of 8.5 Gy 6 Cut-heat TL to 180 ◦ C 7 LM-OSL for 1200 s at 125 ◦ C to obtain the activated LM-OSL

I (t) = 1.6488

LM-OSL (a.u.)

  t2 Im t exp − 2 , tm 2tm

(1)

where Im and tm are the values of the OSL intensity and time, at the maximum of the LM-OSL peak and t the stimulation time. Eq. (1) was used for the deconvolution of all experimental data. The curve fitting was performed using the MINUIT program (James and Roos, 1977), whereas the goodness of fit was tested by the Figure Of Merit (FOM) of Balian and Eddy (1977),

Steps 4–7 are repeated for the same sample by increasing the activation temperature in steps of 10 ◦ C up to 500 ◦ C

a 1E3

2E2

1E3

b

0E0 300

LM-OSL (a.u.)

Patara) one sample from Greece (Chalkidiki) and a synthetic quartz sample of Merck. Laboratory references are Alt, Sle, Atk, Pdk, Pat, Chal and Merck, respectively. The measurements were performed using with the automated RisZ TL/OSL reader (model TL/OSL-DA-15), using an internal 90 Sr/90 Y beta ray source of dose rate ∼ 0.1 Gy/s. Blue light emitting diodes (LEDs) (470 nm, 40 mW/cm2 ) were used for stimulation and the OSL signal was detected through U-340 filters. The ramping rate used was 0.033 mW/cm2 /s, reaching the maximum stimulation power at 1200 s. The measuring protocols used are presented in Table 1.

2E3

5E2

800

1300

a

b 300

3E3

a

800

1300

a

1E3 b

b

300 800 Stimulation time (s)

1300

300 800 Stimulation time (s)

1300

Fig. 1. LM-OSL curves. (A) Atk quartz, (B) Pdk quartz, (C) Chal quartz and (D) Merck quartz. In each case curves (a) correspond to LM-OSL received at RT and curves (b) to LM-OSL received at 125 ◦ C.

N.G. Kiyak et al. / Radiation Measurements 43 (2008) 263 – 268

265

LM-OSL (a. u.)

3E3

2E3

2E3 4

1E3

2

1E3 5

3

5 Bg

3

0E0

0E0 300 800 Stimulation time (s)

Bg

4

300 800 Stimulation time (s)

1300

1300

Fig. 2. Deconvolution of the LM-OSL curve of Atk quartz. (A) LM-OSL received at RT and (B) LM-OSL received at 125 ◦ C. The activation temperature was 370 ◦ C.

5E4

LM-OSL (a. u.)

1E4 4

3E4

3 8E3

1E4

1

1 3

5

2

4 5

3E3

2 Bg 300 800 Stimulation time (s)

Bg 1300

300 800 Stimulation time (s)

1300

Fig. 3. Component resolution of the LM-OSL curve of Chal quartz. (A) LM-OSL received at RT and (B) LM-OSL received at 125 ◦ C. The activation temperature was 410 ◦ C.

given by: FOM =

 |YExper − YFit | i

A

,

(2)

where YExper is the experimental LM-OSL glow-curve, YFit is the fitted LM-OSL glow-curve and A is the area of the fitted LM-OSL glow-curve. Background measurements were performed on many untreated samples for each material. The experimentally obtained background measurements were very well fitted to a straight line of the form bg = a0 + C · t,

(3)

Table 2 The peak maximum time tm of component 4 of the LM-OSL curves of all quartz samples measured at RT; the ratio (%) of OSL at 125 ◦ C over the OSL at 25 ◦ C, of components 1, 2 and 3 and of component 4 over the TL of the 110 ◦ C glow-peak Sample

tm (s)

C4 /TL

C123 (%)

C4 (%)

Alt Atk Pdk Sle Pat Chal Merck

344.0 ± 6.0 366.0 ± 8.0 338.0 ± 5.0 327.0 ± 6.0 381.0 ± 3.0 463.0 ± 18.0 556.0 ± 10.0

97.5 ± 8.0 61.0 ± 5.0 41.0 ± 3.0 46.0 ± 2.0 24.0 ± 3.0 40.0 ± 2.0 55.0 ± 6.0

15.0 ± 1.0 26.0 ± 8.0 45.0 ± 4.0 44.0 ± 2.0 97.0 ± 6.0 68.0 ± 15.0 28.0 ± 4.0

4.2 ± 1.3 6.3 ± 1.2 5.3 ± 1.3 12.0 ± 3.5 17.0 ± 2.0 11.0 ± 3.5 1.4 ± 0.5

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1.8E5

Integral

1.6E6

a

c b

1.2E5

1.0E6

a

4.0E5

b

6.0E4

0.0E0 200

300 400 500 Activation Temperature (°C)

200

300 400 500 Activation Temperature (°C)

Fig. 4. Thermal activation curves (TAC) for Atk quartz. (A) LM-OSL received at RT and (B) LM-OSL received at 125 ◦ C. Curve (a) of LM-OSL components 1, 2 and 3; curve (b) of the LM-OSL component 4; and curve (c) of the TL glow-peak at 110 ◦ C.

5.0E6

Integral

5.0E7

c

a

3.0E6 3.0E7

b b

1.0E7

200

a

300 400 500 Activation Temperature (°C)

1.0E6

200

300 400 500 Activation Temperature (°C)

Fig. 5. Thermal activation curves (TAC) for Chal quartz. (A) LM-OSL received at RT and (B) LM-OSL received at 125 ◦ C. Curve (a) of LM-OSL components 1, 2 and 3; curve (b) of the LM-OSL component 4; and curve (c) of the TL glow-peak at 110 ◦ C.

where a is the OSL signal at t = 0. The values of a and C were evaluated for each kind of quartz and used during deconvolution. 4. Results and discussion Typical LM-OSL curves are shown in Fig. 1, where Fig. 1(A) corresponds to the Atk quartz (similar shape was also measured for Alt quartz) and Fig. 1(B) corresponds to the Pdk quartz (similar shapes were also shown from Sle and Pat quartz). Figs. 1(C) and (D) correspond to Chal and Merck quartz

respectively, which have an intense TL glow-peak at 110 ◦ C. In all cases curve (a) corresponds to LM-OSL measured at RT and curve (b) to LM-OSL measured at 125 ◦ C. It is obvious that the very intense LM-OSL component between 300 and 400 s appears only at RT LM-OSL measurements for all quartz samples. The deconvolution analysis was applied to all experimental LM-OSL curves. The FOM values obtained were around 1% for the RT LM-OSL curves and up to 2% for the LM-OSL curves received at 125 ◦ C due to lower statistics. In the case of Alt, Atk, Pdk and Sle quartz, Kiyak et al. (2007) had used

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267

2.0E5

Integral

1.3E7

c

a

8.0E6

1.0E5

b 3.0E6

b

a 0.0E0

200

300 400 500 Activation Temperature (°C)

200

300 400 500 Activation Temperature (°C)

Fig. 6. Thermal activation curves (TAC) for Merck quartz. (A) LM-OSL received at RT and (B) LM-OSL received at 125 ◦ C. Curve (a) of LM-OSL components 1, 2 and 3; curve (b) of the LM-OSL component 4; and curve (c) of the TL glow-peak at 110 ◦ C.

six components for LM-OSL curves extended up to 3500 and 7200 s. The fifth component with tm at about 1000 s was a shoulder to the very intensive sixth component with tm at about 5500 s (Kitis et al., 2007). The same number of components was also used in the present case. However, since, in the present work, the LM-OSL time was only 1200 s the fifth and sixth components are degenerated into one having the form of a straight line. The reason is that at the very low times of an LM2 ) of Eq. (1) is unity and term OSL peak the term exp(−t 2 /2tm 1.6488 t (Im /tm ) dominates. Examples of the deconvolution analysis are shown in Figs. 2 and 3. Fig. 2(A) presents the deconvolution of the LM-OSL curve Atk quartz measured at RT, whereas Fig. 2(B) the LM-OSL curve of the same sample received at 125 ◦ C. Similarly, Figs. 3(A) and (B) show the case of the Chal quartz at RT and at 125 ◦ C, respectively. Component 4 of all quartz samples is of special interest. Its time maximum tm is shown in Table 2. The areas under the various components are also shown in Table 2 in which the ratio C4 /TL represent the photobleaching part of the TL glow-peak at 110 ◦ C. The third and fourth columns represent the ratio of the LM-OSL at 125 ◦ C over the LM-OSL at RT for components 1, 2 and 3 and for component 4, respectively. The individual behaviors of components 1, 2 and 3 are similar, so they are treated together. The results concerning the last component (fifth) are not included here, since it corresponds only to a minor part of a main component whose tm is above 5000 s. Component 4 appears only at LM-OSL measurements at RT. Therefore, this component must be closely correlated with the TL glow-peak at 110 ◦ C. However, a low-intensity component 4 appears also at LM-OSL measurements at 125 ◦ C. The question whether it is the same component is very crucial. Probably it is

not. Component 4 of the LM-OSL at 125 ◦ C exists also in the case of LM-OSL at RT, but due to its low intensity and about the same tm with main component 4 of the LM-OSL at RT it cannot be resolved from it. This argument is confirmed by the fact that components 1, 2 and 3 are present in both LM-OSL measuring temperatures and that, as it is shown in Table 2, the ratio of the LM-OSL at 125 ◦ C over the LM-OSL at RT for components 1, 2 and 3 is much higher than that of component 4. Therefore, the representative LM-OSL curve is that of 125 ◦ C; the LM-OSL at RT and the contribution from the component due to the TL glow-peak at 110 ◦ C is added over the original component 4, which is due to some other deeper electron trap. It is an interesting observation that the tm values of components 1, 2 and 3 appear in a time region below 200 s, i.e. quite shorter than that of the main component 4, which must be related with the photo-bleaching signal of the TL glow-peak at 110 ◦ C. Additionally, since components 1, 2 and 3 are present at both LM-OSL measuring temperatures they are not related with the photo-bleaching part of the 110 ◦ C glow-peak. Thermal activation results are shown in Figs. 4–6. In Figs. 4–6, the figures (A) correspond to LM-OSL at RT and figures (B) to LM-OSL at 125 ◦ C. Curves (a) in Figs. 4–6 (A,B) correspond to the sum of components 1, 2 and 3; curves (b) to the LM-OSL component 4 and curves (c) to the TAC behavior of the TL integral of the glow-peak at 110 ◦ C. The main result from Figs. 4–6 is that all LM-OSL components, not only component 4 related with the photo-bleaching signal of the TL glow-peak at 110 ◦ C, show the same TAC characteristics. The very good qualitative agreement between all the LM-OSL components and the glow-peak at 110 ◦ C ensures the use of the TL glow-peak at 110 ◦ C as well as the use of any one of the LM-OSL components as an appropriate sensitivity corrector due to thermal activation of the samples.

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5. Conclusion Summarizing, the data of the present work lead to the conclusion that the sensitization of both LM-OSL and TL are due to common mechanism. This argument is in agreement with previous ones like for example the one of Aitken and Smith (1988). On the other hand, due to the fact that this result is common in so many different quartz samples, the above conclusion is a rather universal property holding for any kind of quartz. The origin of component 4 of the LM-OSL measured at RT was attributed to the photo-bleaching part of the TL glow-peak at 110 ◦ C. In this case one expects not only a qualitative but a quantitative agreement too. However, as it is shown in the third column of Table 2 this happens only for the case of Alt quartz. In all other kinds of quartz (Table 2) the LM-OSL of component 4 is more or 50% of the TL glow-peak at 110 ◦ C. This qualitative lack cannot be, of course, adequately explained, when so many LM-OSL and TL glow-peaks are present. However, a possible explanation which could account for the difference between the intensities of the glow-peak at 110 ◦ C and LM-OSL component 4 is based on the difference between thermal and optical release of the electrons from an electron trap. A basic principle of the phenomenological model on which the elementary theory of both TL and OSL is based that once the electrons are thermally or optically released they retain no memory about their origin in the conduction band. Subsequently, their recombination to luminescence centers depends on the way the luminescence centers are distributed, i.e. if they are randomly distributed or they are locally correlated. During the TL readout the electrons are released from their traps in a definite order, which is also followed by their subsequent recombination to luminescence centers. On the other hand

during optical stimulation the electrons are released, with different cross-sections of course, but simultaneously from all existing electron traps in an order different from that of the TL readout. The consequence, of this simultaneous release is an increased competition during recombination and probably an increase of the non-radiative pathways. References Aitken, M.J., Smith, B.W., 1988. Optical dating: recuperation after bleaching. Quat. Sci. Rev. 7, 387–393. Bailiff, I.K., 1994. The pre-dose technique. Radiat. Meas. 23, 471–479. Balian, H.G., Eddy, N.W., 1977. Figure-Of-Merit (FOM). An improved criterion over the normalized Chi-squared test for assessing goodness-of-fit of gamma-ray spectral peaks. Nucl. Instrum. Methods 145, 389–395. Bulur, E., 1996. An alternative technique for optically stimulated luminescence (OSL) experiment. Radiat. Meas. 26, 701–709. Chen, G., Li, S.-H., Murray, A.S., 2000. Study of the 110 ◦ C TL peak sensitivity in optical dating of quartz. Radiat. Meas. 32, 641–645. James, F., Roos, M., 1977. MINUIT, CERN program library entry D506. http://consult.cern.ch/writeups/minuit. Kitis, G., Polymeris, G.S., Kiyak, N.G., 2007. Component-resolved thermal stability and recuperation study of the LM-OSL curves of four sedimentary quartz samples. Radiat. Meas. 42 (8), 1273–1279. Kiyak, N.G., Polymeris, G.S., Kitis, G., 2007. Component resolved OSL dose response and sensitization of various sedimentary quartz samples. Radiat. Meas. 42 (2), 144–155. Koul, D.K., Chougaonkar, M.P., 2007. The pre-dose phenomenon in the OSL signal of quartz. Radiat. Meas. 42 (8), 1265–1272. Murray, A.S., Roberts, R.G., 1998. Measurement of the equivalent dose in quartz using a regeneration-dose single-aliquot protocol. Radiat. Meas. 29, 503–515. Polymeris, G.S., Tsirliganis, N., Loukou, Z., Kitis, G., 2006. A comparative study of the anomalous fading effects of TL and OSL signals in Durango apatite. Phys. Status Solidi (a) 203 (3), 578–590. Wintle, A.G., Murray, A.S., 1998. Towards the development of a preheat procedure for OSL dating of quartz. Radiat. Meas. 29, 81–94.