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Alpha efficiency determination for OSL of quartz extracted from Chinese loess
Radiation Measurements 43 (2008) 767 – 770 www.elsevier.com/locate/radmeas
Alpha efficiency determination for OSL of quartz extracted from Chinese loess Zhong Ping Lai a,b,c,∗ , Ludwig Zöller b , Markus Fuchs b , Helmut Brückner c a Luminescence Dating Laboratory, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, XiNing 810008, PR China b Geomorphology Group, University of Bayreuth, D-95440 Bayreuth, Germany c Faculty of Geography, University of Marburg, D-35032 Marburg, Germany
Abstract We report here the estimates of alpha efficiency for fine grain quartz extracted from Chinese loess using the SAR protocol. For the seven samples, the -values range from 0.028 to 0.038 with an average of 0.035 ± 0.001. The annealed quartz (450 ◦ C, 45 min) has an -value of 0.030 ± 0.001 which is similar to the -value of 0.029 ± 0.001 for the non-annealed quartz extracts, suggesting that the -value is independent of the quartz’s thermal history for this sample. We suggest that an -value of 0.035 ± 0.003 can be adopted for quartz extracted from Chinese loess when calculating the environmental dose rate. © 2008 Elsevier Ltd. All rights reserved. Keywords: Alpha efficiency; Quartz; Chinese loess; Luminescence; OSL
1. Introduction Loess is an aeolian deposit and thus ideal for luminescence dating. For typical loess, it is often difficult to extract enough sand-sized grains (> 90 m), therefore fine (4–11 m) or siltsized (ca. 40–70 m) grains are separated for dating. For siltsized grains it is not possible to remove the outer layer of 20 m in order to eliminate most of the volume affected by alpha particles from the matrix. This requires the measurement of alpha efficiency (AE) for the estimation of the alpha contribution to the environmental dose rate. Using a multi-aliquot method, Rees-Jones (1995) measured the AE for optically stimulated luminescence (OSL) of fine grain quartz for four fluvial samples. These -values ranged from 0.032 to 0.043 (average of 0.04). Tribolo et al. (2001) for the first time employed the standard SAR protocol (Murray and Wintle, 2000) to determine the AE. In their archaeological burnt quartzite pebbles, they found that the TL and OSL growth curves of alpha irradiation behave differently, with -values of TL being higher than that of OSL, ∗ Corresponding author at: Luminescence Dating Laboratory, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, XiNing 810008, PR China. E-mail addresses: [email protected], [email protected] (Z.P. Lai).
1350-4487/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.01.022
and that OSL AE is independent of the past thermal history. Mauz et al. (2006) used samples from both North America and Europe, and demonstrated that the AE for fine grain quartz is independent of sample origin. They suggested that an -value of 0.03 can be adopted. In the case of TL from burnt flints, the AE may be sample dependent, and its value has to be determined for each sample (Mercier et al., 1995). The luminescence signal induced by alpha particles is related to its range (with an average of 20 m in quartz), and it is a linear function of the integrated alpha flux (Aitken, 1985a). In order to evaluate the AE during the initial stage of TL dating of pottery, Zimmerman (1971) introduced a -value to describe the efficiency of alpha irradiation relative to beta irradiation, which was defined as the ratio of the TL per unit absorbed alpha dose to the TL per unit absorbed beta dose. However, for alpha particles, the absorbed dose is strongly dependent on the particle energy so that the -value varies with alpha energy of alpha particles, which has a spectrum from 0 to 8 MeV for alpha particles received from the U and Th decay chains during burial (Aitken, 1985a, b). In order to avoid this drawback, Aitken and Bowman (1975) developed the -value system, which was expressed as the ratio of TL per unit alpha track length to the TL per unit absorbed beta dose. In this system, the TL per unit
768
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
alpha track length is nearly independent of the energy, and so is the -value. Aitken (1985b) described in detail the numerical relationship between the two systems and concluded that for a sample having an alpha stopping power ratio r relative to quartz: = r ∗ 3.7 ,
(1)
where is the -value, 3.7 is the -value if using an alpha source delivering 3.7 MeV alpha particles to a thin layer of quartz. 2. Research design In the current study the value of r is 1, because the sample used is the fine grain quartz. Furthermore, the alpha source used in the laboratory is 241 Am that delivers 3.7 MeV alpha particles; thus = , i.e. -value is equal to -value. This allows for the measurements of the -value using the -value concept in terms of absorbed dose without the calculation of track length of alpha particles. This assumes that the OSL signal is a linear function of the integrated alpha flux and the beta dose (Aitken, 1985a). For the determination of the AE, the SAR protocol is used. First, an aliquot is given a fixed alpha dose (Dalpha ) using a 241 Am source, then it is treated as natural to obtain D by e constructing a beta growth curve. Thus, the AE can be expressed as the ratio of De to Dalpha . The fixed alpha dose should be determined in the way so that the De is no more than about 10 Gy, and therefore well within the linear part of the beta growth curve for quartz. However, the De should not be too small in order to avoid low signal output that may result in a larger statistical error. 3. Samples and measurement techniques Seven samples were selected from five sections following a transect from the east to the west of the Chinese Loess Plateau (for sample details see Table 1). The quartz fraction of 38–63 m was extracted after a series of treatments using HCl and H2 O2 and fluorosilicic acid. To examine the effect of thermal treatment on the AE, some quartz grains of sample CH02/3/24 were annealed in a furnace at 450 ◦ C for 45 min. The quartz of 38–63 m was gently crushed using an agate mortar to obtain 4–11 m grains. The fine grains were then
deposited on aluminium discs. The annealing, crushing and disc making were carried out under normal daylight. Luminescence measurements were carried out in Bayreuth University and on a RisZ TL-DA-15 reader (BZtter-Jensen et al., 2000). The machine was equipped with blue LEDs ( = 470 ± 20 nm) for OSL stimulation, a Thorn-EMI 9235QA photomultiplier for detection, a 90 Y/90 Sr beta source (9.66 Gy/min for fine grains), and a calibrated 241 Am alpha source (8.79 Gy/min for fine grains) for laboratory irradiation. The alpha source was calibrated against the alpha source from the Forschungsstelle Archaeometrie at the Max-Planck Institute of Nuclear Sciences in Heidelberg. OSL was recorded using a U-340 filter with a thickness of 7.5 mm. 4. Experimental details and results As having been discussed in Section 2, the fixed alpha dose, Dalpha , should lie within the dose range of the linear luminescence growth. In order to determine the value of Dalpha an alpha growth curve was constructed using the SAR protocol (Murray and Wintle, 2000). The preheat is chosen to be 260 ◦ C for 10 s, and the cut-heat at 220 ◦ C for 10 s. Ten aliquots of sample CH02/2/1 were used, and they were first fully bleached by daylight before SAR procedures. Alpha regeneration doses are 80, 155, 200, 300, 500, 750, 1000, 1500, 0, and 200 Gy, and the alpha test dose is 100 Gy. OSL measurements were carried out at 130 ◦ C for 60 s. The OSL of the first 0.96 s (1–4 channels) was integrated for the construction of an alpha growth curve. The growth curves of the 10 aliquots were shown in Fig. 1, together with the average growth curve (empty circle) for the 10 aliquots. It is clear that, up to 500 Gy, the luminescence growth is linear (R 2 = 0.998) (see insert in Fig. 1). As a result, the Dalpha is chosen to be 250 Gy. The growth curves for the 10 aliquots overlap each other, suggesting that there is a common growth curve for different aliquots (Roberts and Duller, 2004; Lai, 2006; Lai et al., 2007a). For the construction of a beta growth curve, beta regeneration doses are set to be 6, 9, 12, 15, 0, and 6 Gy, with a beta test dose of 5.8 Gy. A beta growth curve was shown in Fig. 2. In order to check the validity of the SAR protocol for equivalent dose determination, a laboratory beta dose recovery test (Murray and Wintle, 2003) was conducted for one sample CH02/2/1, using 11 aliquots. A beta laboratory dose of 9 Gy was administered to an aliquot after being bleached twice by
Table 1 Sample information and -value results No.
Sample ID
Sectiona name
1 2 3 4 5 6 7 8
BW20 LC30 LT/0.8 CH02/5/2 CH02/2/1 CH02/2/2 CH02/3/24 CH02/3/24 annealed
Bianwan Luochuan Lingtai Jiuzhoutai Yuanbao Yuanbao Yuanbao Yuanbao
a The
Natural De (Gy)
Age (ka)
Saturated 1.5 10 114 114
<1 c. 60 c. 15 c. 750 0.44 3.1 34 34
Reference
Lai Lai Lai Lai Lai
(2006) (2006) and Wintle (2006) and Wintle (2006) et al. (2007b)
section names were listed in order from the east to the west throughout the Chinese Loess Plateau.
Number of aliquots
-Value
Error
11 12 15 14 14 16 16 12
0.037 0.028 0.037 0.038 0.036 0.037 0.029 0.030
0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
known laboratory dose can be successfully recovered and that there is no significant trap probability change triggered by the first preheat (Wallinga et al., 2000; Lai et al., 2006). The SAR conditions described above were employed for the AE determination. An alpha dose of 250 Gy was applied to an aliquot. This aliquot was then treated as natural to obtain De . The AE then is the ratio of De to the value of the alpha dose of 250 Gy. Eleven to 16 aliquots were used for each of the eight samples. The results are listed in Table 1.
Normalised OSL
12
8 6 4 4
2
5. Conclusions
0 0
200
400
600
0 500
0
1000 Alpha Dose (Gy)
1500
2000
Fig. 1. Regeneration dose points for alpha irradiation for 10 aliquots of sample CH02/2/1, together with their average growth curve (empty circle). Up to 500 Gy, the luminescence growth is linear (see inset).
OSL Intensity (c/0.24s)
5000 15 Gy beta dose
4000
769
The -values for the seven samples range from 0.028 to 0.038 with an average of 0.035 ± 0.001. It is not clear what causes the variation. There is no tendency of -values for samples from the east to the west in the Chinese Loess Plateau. Also, no correlation could be observed between the -values and the ages. The annealed quartz (450 ◦ C for 45 min) has an -value (0.030 ± 0.001) similar to the un-annealed grains (0.029 ± 0.001) for sample CH02/3/24, confirming the previous result that the -value is independent of its thermal history (Tribolo et al., 2001). We recommend that an -value of 0.035 ± 0.003 can be adopted for quartz extracted from Chinese loess when calculating the environmental dose rate. Acknowledgements
3000 250 Gy alpha dose
Z.P.L. thanks the Alexander von Humboldt Foundation for a Research Fellowship. Alexander Fülling helped in the measurement of the alpha growth curve. Also supported by a OneHundred Talents Project, CAS. We thank an anonymous referee for helpful comments.
2000 beta test dose of 5.8 Gy 1000 0 Gy 0 0
2
4 6 Stimulation Time (s)
8
10
References
Normalised OSL
3
2
1
0 0
5
10 Beta Dose (Gy)
15
20
Fig. 2. (a) OSL decay curves and (b) a growth curve for sample CH02/2/2.
stimulation with blue LEDs for 60 s at 130 ◦ C. The aliquot was then treated as natural to obtain De by SAR. The recovered De is 8.87 ± 0.12 Gy (average of 11 aliquots), suggesting that a
Aitken, M.J., 1985a. Thermoluminescence Dating. Academic Press, London. Aitken, M., 1985b. Alpha particle effectiveness: numerical relationship between systems. Ancient TL 3, 22–25. Aitken, M.J., Bowman, S.G.E., 1975. Thermoluminescent dating: assessment of alpha particle contribution. Archaeometry 17, 132–138. BZtter-Jensen, L., Bulur, E., Duller, G.A.T., Murray, A.S., 2000. Advances in luminescence instrumentation. Radiat. Meas. 32, 523–528. Lai, Z.-P., 2006. Testing the use of an OSL standardised growth curve (SGC) for De determination on quartz from the Chinese Loess Plateau. Radiat. Meas. 41, 9–16. Lai, Z.-P., Wintle, A.G., 2006. Locating the boundary between the Pleistocene and the Holocene in Chinese loess using luminescence. Holocene 16, 893–899. Lai, Z.-P., Murray, A., Bailey, R., Huot, S., BZtter-Jensen, L., 2006. Quartz red TL SAR equivalent dose overestimation for Chinese loess. Radiat. Meas. 41, 114–119. Lai, Z.-P., Brückner, H., Zöller, L., Fülling, A., 2007a. Existence of a common growth curve for silt-sized quartz OSL of loess from different continents. Radiat. Meas. 42, 1432–1440. Lai, Z.-P., Wintle, A.G., Thomas, D.S.G., 2007b. Rates of dust deposition between 50 ka and 20 ka revealed by OSL dating at Yuanbao on the Chinese Loess Plateau. Palaeogeogr. Palaeoclimatol. Palaeoecol. 248, 431–439. Mauz, B., Packman, S., Lang, A., 2006. The alpha effectiveness in silt-sized quartz: new data obtained by single and multiple aliquot protocols. Ancient TL 24, 47–52.
770
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
Mercier, N., Valladas, H., Valladas, G., Reyss, J.L., Jeline, K.A., Meignen, L., Joron, J.L., 1995. TL dates of burnt flints from Jelinek’s excavations at Tabun and their implications. J. Archaeol. Sci. 22, 495–509. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiat. Meas. 32, 57–73. Murray, A.S., Wintle, A.G., 2003. The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiat. Meas. 37, 377–381. Rees-Jones, J., 1995. Optical dating of young sediments using fine-grain quartz. Ancient TL 13, 9–14.
Roberts, H.M., Duller, G.A.T., 2004. Standardised growth curves for optical dating of sediment using multiple-grain aliquots. Radiat. Meas. 38, 241–252. Tribolo, C., Mercier, D., Valladas, H., 2001. Alpha sensitivity determination in quartzite using an OSL single aliquot procedure. Ancient TL 19, 47–50. Wallinga, J., Murray, A., Duller, G., 2000. Underestimation of equivalent dose in single-aliquot optical dating of feldspars caused by preheating. Radiat. Meas. 32, 691–695. Zimmerman, D.W., 1971. Thermoluminescence dating using fine grains from pottery. Archaeometry 13, 29–52.
Alpha efficiency determination for OSL of quartz extracted from Chinese loess Zhong Ping Lai a,b,c,∗ , Ludwig Zöller b , Markus Fuchs b , Helmut Brückner c a Luminescence Dating Laboratory, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, XiNing 810008, PR China b Geomorphology Group, University of Bayreuth, D-95440 Bayreuth, Germany c Faculty of Geography, University of Marburg, D-35032 Marburg, Germany
Abstract We report here the estimates of alpha efficiency for fine grain quartz extracted from Chinese loess using the SAR protocol. For the seven samples, the -values range from 0.028 to 0.038 with an average of 0.035 ± 0.001. The annealed quartz (450 ◦ C, 45 min) has an -value of 0.030 ± 0.001 which is similar to the -value of 0.029 ± 0.001 for the non-annealed quartz extracts, suggesting that the -value is independent of the quartz’s thermal history for this sample. We suggest that an -value of 0.035 ± 0.003 can be adopted for quartz extracted from Chinese loess when calculating the environmental dose rate. © 2008 Elsevier Ltd. All rights reserved. Keywords: Alpha efficiency; Quartz; Chinese loess; Luminescence; OSL
1. Introduction Loess is an aeolian deposit and thus ideal for luminescence dating. For typical loess, it is often difficult to extract enough sand-sized grains (> 90 m), therefore fine (4–11 m) or siltsized (ca. 40–70 m) grains are separated for dating. For siltsized grains it is not possible to remove the outer layer of 20 m in order to eliminate most of the volume affected by alpha particles from the matrix. This requires the measurement of alpha efficiency (AE) for the estimation of the alpha contribution to the environmental dose rate. Using a multi-aliquot method, Rees-Jones (1995) measured the AE for optically stimulated luminescence (OSL) of fine grain quartz for four fluvial samples. These -values ranged from 0.032 to 0.043 (average of 0.04). Tribolo et al. (2001) for the first time employed the standard SAR protocol (Murray and Wintle, 2000) to determine the AE. In their archaeological burnt quartzite pebbles, they found that the TL and OSL growth curves of alpha irradiation behave differently, with -values of TL being higher than that of OSL, ∗ Corresponding author at: Luminescence Dating Laboratory, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, XiNing 810008, PR China. E-mail addresses: [email protected], [email protected] (Z.P. Lai).
1350-4487/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.01.022
and that OSL AE is independent of the past thermal history. Mauz et al. (2006) used samples from both North America and Europe, and demonstrated that the AE for fine grain quartz is independent of sample origin. They suggested that an -value of 0.03 can be adopted. In the case of TL from burnt flints, the AE may be sample dependent, and its value has to be determined for each sample (Mercier et al., 1995). The luminescence signal induced by alpha particles is related to its range (with an average of 20 m in quartz), and it is a linear function of the integrated alpha flux (Aitken, 1985a). In order to evaluate the AE during the initial stage of TL dating of pottery, Zimmerman (1971) introduced a -value to describe the efficiency of alpha irradiation relative to beta irradiation, which was defined as the ratio of the TL per unit absorbed alpha dose to the TL per unit absorbed beta dose. However, for alpha particles, the absorbed dose is strongly dependent on the particle energy so that the -value varies with alpha energy of alpha particles, which has a spectrum from 0 to 8 MeV for alpha particles received from the U and Th decay chains during burial (Aitken, 1985a, b). In order to avoid this drawback, Aitken and Bowman (1975) developed the -value system, which was expressed as the ratio of TL per unit alpha track length to the TL per unit absorbed beta dose. In this system, the TL per unit
768
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
alpha track length is nearly independent of the energy, and so is the -value. Aitken (1985b) described in detail the numerical relationship between the two systems and concluded that for a sample having an alpha stopping power ratio r relative to quartz: = r ∗ 3.7 ,
(1)
where is the -value, 3.7 is the -value if using an alpha source delivering 3.7 MeV alpha particles to a thin layer of quartz. 2. Research design In the current study the value of r is 1, because the sample used is the fine grain quartz. Furthermore, the alpha source used in the laboratory is 241 Am that delivers 3.7 MeV alpha particles; thus = , i.e. -value is equal to -value. This allows for the measurements of the -value using the -value concept in terms of absorbed dose without the calculation of track length of alpha particles. This assumes that the OSL signal is a linear function of the integrated alpha flux and the beta dose (Aitken, 1985a). For the determination of the AE, the SAR protocol is used. First, an aliquot is given a fixed alpha dose (Dalpha ) using a 241 Am source, then it is treated as natural to obtain D by e constructing a beta growth curve. Thus, the AE can be expressed as the ratio of De to Dalpha . The fixed alpha dose should be determined in the way so that the De is no more than about 10 Gy, and therefore well within the linear part of the beta growth curve for quartz. However, the De should not be too small in order to avoid low signal output that may result in a larger statistical error. 3. Samples and measurement techniques Seven samples were selected from five sections following a transect from the east to the west of the Chinese Loess Plateau (for sample details see Table 1). The quartz fraction of 38–63 m was extracted after a series of treatments using HCl and H2 O2 and fluorosilicic acid. To examine the effect of thermal treatment on the AE, some quartz grains of sample CH02/3/24 were annealed in a furnace at 450 ◦ C for 45 min. The quartz of 38–63 m was gently crushed using an agate mortar to obtain 4–11 m grains. The fine grains were then
deposited on aluminium discs. The annealing, crushing and disc making were carried out under normal daylight. Luminescence measurements were carried out in Bayreuth University and on a RisZ TL-DA-15 reader (BZtter-Jensen et al., 2000). The machine was equipped with blue LEDs ( = 470 ± 20 nm) for OSL stimulation, a Thorn-EMI 9235QA photomultiplier for detection, a 90 Y/90 Sr beta source (9.66 Gy/min for fine grains), and a calibrated 241 Am alpha source (8.79 Gy/min for fine grains) for laboratory irradiation. The alpha source was calibrated against the alpha source from the Forschungsstelle Archaeometrie at the Max-Planck Institute of Nuclear Sciences in Heidelberg. OSL was recorded using a U-340 filter with a thickness of 7.5 mm. 4. Experimental details and results As having been discussed in Section 2, the fixed alpha dose, Dalpha , should lie within the dose range of the linear luminescence growth. In order to determine the value of Dalpha an alpha growth curve was constructed using the SAR protocol (Murray and Wintle, 2000). The preheat is chosen to be 260 ◦ C for 10 s, and the cut-heat at 220 ◦ C for 10 s. Ten aliquots of sample CH02/2/1 were used, and they were first fully bleached by daylight before SAR procedures. Alpha regeneration doses are 80, 155, 200, 300, 500, 750, 1000, 1500, 0, and 200 Gy, and the alpha test dose is 100 Gy. OSL measurements were carried out at 130 ◦ C for 60 s. The OSL of the first 0.96 s (1–4 channels) was integrated for the construction of an alpha growth curve. The growth curves of the 10 aliquots were shown in Fig. 1, together with the average growth curve (empty circle) for the 10 aliquots. It is clear that, up to 500 Gy, the luminescence growth is linear (R 2 = 0.998) (see insert in Fig. 1). As a result, the Dalpha is chosen to be 250 Gy. The growth curves for the 10 aliquots overlap each other, suggesting that there is a common growth curve for different aliquots (Roberts and Duller, 2004; Lai, 2006; Lai et al., 2007a). For the construction of a beta growth curve, beta regeneration doses are set to be 6, 9, 12, 15, 0, and 6 Gy, with a beta test dose of 5.8 Gy. A beta growth curve was shown in Fig. 2. In order to check the validity of the SAR protocol for equivalent dose determination, a laboratory beta dose recovery test (Murray and Wintle, 2003) was conducted for one sample CH02/2/1, using 11 aliquots. A beta laboratory dose of 9 Gy was administered to an aliquot after being bleached twice by
Table 1 Sample information and -value results No.
Sample ID
Sectiona name
1 2 3 4 5 6 7 8
BW20 LC30 LT/0.8 CH02/5/2 CH02/2/1 CH02/2/2 CH02/3/24 CH02/3/24 annealed
Bianwan Luochuan Lingtai Jiuzhoutai Yuanbao Yuanbao Yuanbao Yuanbao
a The
Natural De (Gy)
Age (ka)
Saturated 1.5 10 114 114
<1 c. 60 c. 15 c. 750 0.44 3.1 34 34
Reference
Lai Lai Lai Lai Lai
(2006) (2006) and Wintle (2006) and Wintle (2006) et al. (2007b)
section names were listed in order from the east to the west throughout the Chinese Loess Plateau.
Number of aliquots
-Value
Error
11 12 15 14 14 16 16 12
0.037 0.028 0.037 0.038 0.036 0.037 0.029 0.030
0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
known laboratory dose can be successfully recovered and that there is no significant trap probability change triggered by the first preheat (Wallinga et al., 2000; Lai et al., 2006). The SAR conditions described above were employed for the AE determination. An alpha dose of 250 Gy was applied to an aliquot. This aliquot was then treated as natural to obtain De . The AE then is the ratio of De to the value of the alpha dose of 250 Gy. Eleven to 16 aliquots were used for each of the eight samples. The results are listed in Table 1.
Normalised OSL
12
8 6 4 4
2
5. Conclusions
0 0
200
400
600
0 500
0
1000 Alpha Dose (Gy)
1500
2000
Fig. 1. Regeneration dose points for alpha irradiation for 10 aliquots of sample CH02/2/1, together with their average growth curve (empty circle). Up to 500 Gy, the luminescence growth is linear (see inset).
OSL Intensity (c/0.24s)
5000 15 Gy beta dose
4000
769
The -values for the seven samples range from 0.028 to 0.038 with an average of 0.035 ± 0.001. It is not clear what causes the variation. There is no tendency of -values for samples from the east to the west in the Chinese Loess Plateau. Also, no correlation could be observed between the -values and the ages. The annealed quartz (450 ◦ C for 45 min) has an -value (0.030 ± 0.001) similar to the un-annealed grains (0.029 ± 0.001) for sample CH02/3/24, confirming the previous result that the -value is independent of its thermal history (Tribolo et al., 2001). We recommend that an -value of 0.035 ± 0.003 can be adopted for quartz extracted from Chinese loess when calculating the environmental dose rate. Acknowledgements
3000 250 Gy alpha dose
Z.P.L. thanks the Alexander von Humboldt Foundation for a Research Fellowship. Alexander Fülling helped in the measurement of the alpha growth curve. Also supported by a OneHundred Talents Project, CAS. We thank an anonymous referee for helpful comments.
2000 beta test dose of 5.8 Gy 1000 0 Gy 0 0
2
4 6 Stimulation Time (s)
8
10
References
Normalised OSL
3
2
1
0 0
5
10 Beta Dose (Gy)
15
20
Fig. 2. (a) OSL decay curves and (b) a growth curve for sample CH02/2/2.
stimulation with blue LEDs for 60 s at 130 ◦ C. The aliquot was then treated as natural to obtain De by SAR. The recovered De is 8.87 ± 0.12 Gy (average of 11 aliquots), suggesting that a
Aitken, M.J., 1985a. Thermoluminescence Dating. Academic Press, London. Aitken, M., 1985b. Alpha particle effectiveness: numerical relationship between systems. Ancient TL 3, 22–25. Aitken, M.J., Bowman, S.G.E., 1975. Thermoluminescent dating: assessment of alpha particle contribution. Archaeometry 17, 132–138. BZtter-Jensen, L., Bulur, E., Duller, G.A.T., Murray, A.S., 2000. Advances in luminescence instrumentation. Radiat. Meas. 32, 523–528. Lai, Z.-P., 2006. Testing the use of an OSL standardised growth curve (SGC) for De determination on quartz from the Chinese Loess Plateau. Radiat. Meas. 41, 9–16. Lai, Z.-P., Wintle, A.G., 2006. Locating the boundary between the Pleistocene and the Holocene in Chinese loess using luminescence. Holocene 16, 893–899. Lai, Z.-P., Murray, A., Bailey, R., Huot, S., BZtter-Jensen, L., 2006. Quartz red TL SAR equivalent dose overestimation for Chinese loess. Radiat. Meas. 41, 114–119. Lai, Z.-P., Brückner, H., Zöller, L., Fülling, A., 2007a. Existence of a common growth curve for silt-sized quartz OSL of loess from different continents. Radiat. Meas. 42, 1432–1440. Lai, Z.-P., Wintle, A.G., Thomas, D.S.G., 2007b. Rates of dust deposition between 50 ka and 20 ka revealed by OSL dating at Yuanbao on the Chinese Loess Plateau. Palaeogeogr. Palaeoclimatol. Palaeoecol. 248, 431–439. Mauz, B., Packman, S., Lang, A., 2006. The alpha effectiveness in silt-sized quartz: new data obtained by single and multiple aliquot protocols. Ancient TL 24, 47–52.
770
Z.P. Lai et al. / Radiation Measurements 43 (2008) 767 – 770
Mercier, N., Valladas, H., Valladas, G., Reyss, J.L., Jeline, K.A., Meignen, L., Joron, J.L., 1995. TL dates of burnt flints from Jelinek’s excavations at Tabun and their implications. J. Archaeol. Sci. 22, 495–509. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiat. Meas. 32, 57–73. Murray, A.S., Wintle, A.G., 2003. The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiat. Meas. 37, 377–381. Rees-Jones, J., 1995. Optical dating of young sediments using fine-grain quartz. Ancient TL 13, 9–14.
Roberts, H.M., Duller, G.A.T., 2004. Standardised growth curves for optical dating of sediment using multiple-grain aliquots. Radiat. Meas. 38, 241–252. Tribolo, C., Mercier, D., Valladas, H., 2001. Alpha sensitivity determination in quartzite using an OSL single aliquot procedure. Ancient TL 19, 47–50. Wallinga, J., Murray, A., Duller, G., 2000. Underestimation of equivalent dose in single-aliquot optical dating of feldspars caused by preheating. Radiat. Meas. 32, 691–695. Zimmerman, D.W., 1971. Thermoluminescence dating using fine grains from pottery. Archaeometry 13, 29–52.