The investigation of irradiation sensitivity of electron spin resonance (ESR) centers is a significant part of the study of ESR signal characteristics and helps to gain insight into the physical mechanisms of paramagnetic centers. In this study, we have observed and compared the irradiation sensitivity characteristics of ESR centers under high-temperature baking in natural conditions by lava flow.
Radiation Measurements 157 (2022) 106823 Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas The relationship between irradiation sensitivity of quartz Al and Ti centers and baking temperature by volcanic lava flow: Example of Datong volcanic group, China Chun-Ru Liu a, Hao Ji a, *, Wen-Peng Li b, Chuan-Yi Wei a, Gong-Ming Yin a, ** a b State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, 100029, China Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China A R T I C L E I N F O A B S T R A C T Keywords: Quartz Electron spin resonance (ESR) Al center Ti center Lava flow Datong volcano group The investigation of irradiation sensitivity of electron spin resonance (ESR) centers is a significant part of the study of ESR signal characteristics and helps to gain insight into the physical mechanisms of paramagnetic centers In this study, we have observed and compared the irradiation sensitivity characteristics of ESR centers under high-temperature baking in natural conditions by lava flow Results show that the irradiation sensitivity of the Al and Ti–Li centers increases with the baking temperature, while the irradiation sensitivity of the Ti–H center increases first (up to ~500 ◦ C) and then decreases with temperature Moreover, the ESR intensity of the Ti center is more strongly dependent on the annealing history of the samples than the Al center In addition, from the results of the heating experiment, after heating above 1000 ◦ C, additional irradiation does not produce new Ti–H signals, which probably indicates that the paleo-temperature of the lava flow in Yujiazhai area did not exceed 1000 ◦ C Introduction Structural defects in solids (charged electron and electron hole traps) may be produced by radioactive elements decaying in the environment The increase in defect concentration is positively correlated with the increase in the accumulation of radiation dose Electron spin resonance (ESR) is one of the main dating techniques which are based on the accumulation of radiation defects in solids being the same as lumines cence dating (Vyatkin and Koshchug, 2020) In ESR dating, lattice de fects with unpaired electrons are analyzed to determine the accumulated dose of radiation and hence the age (Toyoda and Ikeya, 1991) Quartz is one of the most abundant minerals on the surface of the earth which is often used for ESR dating (e.g Grün et al., 1999; Toyoda et al., 2000), such as for fault gouge (e.g Ikeya et al., 1982), volcanic tephra (e.g Imai et al., 1985; Suchodoletz et al., 2012), flint (e.g Porat et al., 1994), and sediment (e.g Yokoyama et al., 1985; Liu et al., 2010) The recent studies of the signal characteristics are mainly focused on the feature of light fading (e.g Yokoyama et al., 1985; Toyoda et al., 2000; Voinchet et al., 2003), thermal behavior (e.g Fukuchi, 1989; Toyoda and Ikeya, 1991; Toyoda et al., 1993; Falgu` eres et al., 1994; Vyatkin and Koshchug, 2020), dose-response (e.g Grün and Macdonald, 1989; Grün and Brumby, 1994; Voinchet et al., 2013; Duval and Guilarte, 2015; Tsukamoto et al., 2018), and potential use for sediment provenance tracing (e.g Tissoux et al., 2015; Wei et al., 2017, 2019), etc Changes in ESR heating, bleaching, and irradiation (Poolton et al., 2000) sensitivity of quartz as a result of laboratory treatments had been studied, however, there are very few studies from natural conditions, in spite of the studies of luminescence dating, which is similar to the ESR principle, many sensitivity studies have been carried out and a lot of reliable results have been achieved (e.g Lai and Wintle, 2006; Zheng et al., 2009; Lü and Sun, 2011) So it was significantly necessary to check the feature of the sensitivity (mainly irradiation) of ESR centers in nat ural conditions The Quaternary Datong volcanic group (DVG) is the most important monogenetic volcanic region in eastern China The volcanic basalt overlays the lacustrine strata, forming the baking strata with different temperatures, and the closer to the basalt, the higher the baking tem perature The lacustrine strata baked by lava flow provides a good natural sample for the study of sensitivity characteristics of quartz ESR centers because compared with the result of laboratory treatments: 1) * Corresponding author ** Corresponding author E-mail addresses: jihao9610@126.com (H Ji), yingongming@ies.ac.cn (G.-M Yin) https://doi.org/10.1016/j.radmeas.2022.106823 Received 30 November 2021; Received in revised form 15 June 2022; Accepted 29 June 2022 Available online July 2022 1350-4487/© 2022 Elsevier Ltd All rights reserved C.-R Liu et al Radiation Measurements 157 (2022) 106823 the characteristics of quartz baked by lava flow are the same because of the same provenance of sediments (Wang et al., 2002); 2) after depo sition the lacustrine strata have been baked at different temperatures from high (hundreds or even over a thousand) to low (natural envi ronment temperature) depending on the depth; 3) the sample was baked in the air, not in the oven; 4) the raw sediment was baked, not just quartz grains; 5) the baked time was much longer, days or even months; 6) after baking, the sample was irradiated at the natural dose rate rather than artificially irradiated at to 10 orders of magnitude higher than the natural dose rate; 7) before baking, the lacustrine sediments was bleached under natural sunlight; 8) judging from the characteristics of the lacustrine sediments closest to the basalt, water should be involved in the lava flow baking Therefore, in the present study, we have observed and compared the irradiation sensitivity (the amount of signal growth per unit dose) characteristics of quartz ESR centers in natural conditions by lava flow In addition, according to the heating experiment, we estimated the paleo-temperatures of the lava flow and the associated baking layers Zhao et al., 2012; Zhao et al., 2015) The sampling site is located on the north bank of Cetian Reservoir the southwest of Yujiazhai village, and the southeast of DVG (Fig 2) The upper part of the sample section is covered with basalt which has a thickness of about m Chen et al (1986) used the K–Ar method to determine the average age of basalt in Cetian Reservoir as ~0.4 Ma The baked layer is about 1.2 m and has a distinct red color compared with the unfired layer (Liu et al., 2015) According to the baking color and degree, from high to low, the baked layer can be divided into four parts (Fig 2): (1) sintering layer Indirect contact with lava flow, due to high temperature and pressure, the loose sediments consolidated into hard blocks with brick red color and thickness of ~10 cm, with numerous pores and rolling structure The basalt is inclined upward at the contact surface between the basalt and lacustrine layer (2) High temperature quenched layer, located in the lower part of the sintered layer, between 10 and 20 cm deep It is speculated that water is involved in baking, so it shows the characteristics of high-temperature quenching, gray and looseness, spherical structure, and more pores (Fig 2c) (3) High baking temperature layer at a depth between 20 cm and 80 cm, dense and dark red (4) Low baking temperature layer at a depth between 80 cm and 120 cm, dense and yellow-green, and the grain size of the sediment is smaller than for the upper layers (5) The typical lacustrine layer is located at depths below 120 cm, yellow-white and dense It contains a cm thick calcium carbonate plate at the depth of 160 cm (Fig 2e) We sampled sediments in these different layers (0–10, 10–20, 30–40, 50–60, 70–80, 90–100, 110–120, 130–140, 150–160, and 170–180 cm) and named them S1-10 to evaluate the impact of the baking temperature on the quartz ESR centers under natural conditions, and in order to evaluate the dose rates of sample S1 and S2, we also collected a basalt sample (B1) at about 10 cm from the top of the lacustrine layer for analysis (Fig 2) Samples The sample site is located in the central part of Nihewan Basin, and the Sanggan River flows through Nihewan Basin from west to east Typical lacustrine strata (tens of meters thick) are widely distributed in Nihewan Basin along the banks of the Sanggan River The sedimentary deposit studied is considered to be homogeneous and the quartz initially (before baking) should have the same physical properties The Cetian Reservoir was built on the Sanggan River in the Nihewan Basin The lava flow from DVG, located in the eastern part of Datong City, covered the lacustrine strata at the north bank of Cetian Reservoir (Fig 1) There are at least 13 volcanic cones in the western part of the DVG, composed predominantly of alkali basalt produced by central-vent eruptions, while the eastern part of the DVG is dominated by lava flow composed mainly of tholeiites produced by fissure eruptions (e.g Zhang, 1986; Basu et al., 1991; Li and Xu, 1995; Xu et al., 2005) Volcanism in the western part of the DVG dates from the late Middle Pleistocene, at ~0.4 Ma, while in the eastern part it dates from the early Middle Pleistocene, at ~0.76 Ma (e.g Kaneoka et al., 1983; Chen et al., 1992; Cheng et al., 2006) However, the timing of the ending of volca nism in the region has been debated for several decades (e.g Pei, 1981; Zhou et al., 1982; Li and Sun, 1984; Zhu et al., 1990; Chen et al., 1992; Experimental procedures 3.1 Quartz extraction and irradiation There is a significant difference in grain size between the upper and lower It is clayey silt at the depth of 0–80 cm, and silty clay below 80 cm So, it is hard to separate the fraction larger than 100 μm below 80 cm For comparing the natural signal intensity of quartz, 80–100 μm fraction in all the samples was chosen to avoid any difference caused by Fig Location map of the study area and sampling site C.-R Liu et al Radiation Measurements 157 (2022) 106823 Fig Sampling profile of Yujiazhai and sample locations on the profile different quartz particle sizes After sieving, pure quartz was obtained through chemical separation techniques detailed by Liu et al (2010) For investigating the irradiation sensitivity change, six samples of different baking characteristics were selected for the study: S1and S2 were selected for different colors and features; S3 and S5 were selected with 30 cm intervals for S3, S4 and S5 have the same color and features; S7 was selected to be 30 cm from S5 for S6 and S7 have the same color and features; S8 was selected because it is hard to extract enough quartz in S9 and S10 for higher calcium content The quartz grains extracted from six samples (S1, S2, S3, S5, S7, and S8) were divided into several 200 mg aliquots, seven of them were irradiated using a60Co gamma source with the dose range of 109–2072 Gy a Bruker ER-041-XG X-band spectrometer in a finger dewar cooled to 77 K with liquid nitrogen, in the ESR laboratory of the Institute of Geology, China Earthquake Administration, Beijing The experimental parame ters were: microwave power mW and modulation amplitude 0.16 mT The Al center intensity was measured from the top of the first peak to the bottom of the 16th peak (Yokoyama et al., 1985) The Ti–Li center in tensity was taken from the top of the peak at g = 1.979 to the bottom at g = 1.913 (Rink et al., 2007; Liu et al., 2010) and the average of the two peaks near g = 1.986 to the baseline is used as the signal intensity of the Ti–H center Fig showed the natural S3 sample ESR spectrum at low temperature (77K, liquid nitrogen) Considering the angular depen dence of the ESR signal due to the sample heterogeneity, each aliquot was measured six times after a rotation of 60◦ angle in the cavity to obtain the average intensity 3.2 ESR measurement The ESR intensities of both the Al and Ti centers were measured with C.-R Liu et al Radiation Measurements 157 (2022) 106823 Results 4.1 ESR measurement of natural (non-irradiated) aliquots In this section we want to compare quantificationally the ESR signal intensity of natural quartz because quartz at different depths: 1) theo retically, has the same provenance and the same transport and deposi tion process before deposition; 2) after deposition, was partial or complete thermal bleaching by lava flow depending on the depth; 3) after baking, was irradiated continuously at natural dose rate for hun dreds of thousands of years The dose rates were shown in Table 1, range of 2.72–3.17 Gy/ka, low in the upper layer and high in the lower layer Theoretically, if there is no change in irradiation sensitivity characteristics of quartz ESR centers at different depths, the intensity of quartz ESR centers should increase with the depth according to stratigraphic order However, the ESR in tensity of quartz at different baking layers varies greatly The natural quartz ESR spectrum of several samples (S1, S4, S7, and S10) at low temperature (77K) were shown in Fig Fig ESR spectrum showing the intensity of the Al, Ti–Li, and Ti–H centers in natural sample S3 (77K, liquid nitrogen) 3.3 Dose rate 4.1.1 The Al center Fig 5a shows the evolution of the Al center signal intensity versus the depth of sampling It can be divided into three stages: 1) During the first stage, between 180 and 130 cm, the signal intensity does not change significantly 2) The second stage corresponds to a rapid decrease of signal intensity between 130 and 50 cm 3) The third stage corresponds to a rapid increase of intensity between 50 cm and the top of the sequence Considering the dose rate and stratigraphic order, the Al center in tensity of the second stage (130-50 cm) should be equal to or slightly less than that of the first stage (180-130 cm) The Al center intensity of the second stage is much smaller than that of the first stage because the quartz was baked at high temperatures (over 220 ◦ C), and the ESR in tensity of the Al center decrease at 220 ◦ C (Toyoda and Ikeya, 1991), and then released Dose rate is one of the factors to compare ESR signal characteristics of quartz in different baking layers (see 4.1 section) The external dose rate consists of the beta and gamma dose rates from the radioactive el ements (U, Th, K) in the sediments immediately surrounding the sample, plus the contribution from cosmic rays However, as a result of the gamma rays having an average range of 30 cm, the calculation of the gamma dose rate for samples S1 and S2 should take into account the contribution of the overlying basalt Considering the depths of samples S1 and S2, we estimate the contribution ratios of basalt and sediment to gamma dose rate as 1:1 and 1:3, respectively Radioactive elements (U, Th, K) concentrations were determined by ICP-OES/MS analysis of the natural sediments and basalt The external alpha dose rate was not considered for hydrofluoric acid etching in quartz extraction (Liu et al., 2010) The external beta and gamma dose rates were derived using the dose rate conversion factors from Gu´erin et al (2011) We assumed a grain size of 90 μm for beta ray attenuation, and the attenuation factor is 0.93 (Mejdahl, 1979) Since the sediments were dry at the time of sampling, current water is more likely underestimated in comparison with the past water content, and therefore it is estimated to be 10% concerning previous ESR studies in the Nihewan Basin (The lacustrine strata are the same set of sedimentary stratigraphy as in the Nihewan Basin) (Liu et al., 2010, 2013, 2014) In addition, the water content of basalt is considered to be 0% The cosmic dose rate contributions were calculated using the formulae proposed by Prescott and Hutton (1988), with depth, altitude, and latitude corrections (Prescott and Hutton, 1994) 4.1.2 The Ti center There are three types of Ti centers according with the nature of the compensator cations: Ti–Li center, Ti–H center and Ti–Na center The Ti–Na center is however very rarely observed in natural quartz In this study, we did not observe the presence of this center in middle and lower layer (S5, S6, S7, S8, S9 and S10), so we will just discuss the signal characteristics of the Ti–Li and Ti–H centers The signal intensity of the Ti–Li center remains basically unchanged for the lower part of the sequence from 180 to 130 cm depth, then de creases to the minimum value at 90 cm, and then increases slowly with the increasing baking temperature at the depth between 90 and 30 cm, before to lastly grows rapidly until the top of the section, as shown in Fig 5b The Ti associated donor electrons are recombining predominantly at the [AlO4]0 acceptors The annealing process may lead directly to the Table Dose rates for samples S1–S10 and B1 from the Yujiazhai profile Sample No Depth (cm) U (ppm) Th (ppm) K (%) Water content (%) Dβ (Gy/ka) Dγ (Gy/ka) Dcos (Gy/ka) Dtotal (Gy/ka) S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 B1 15 35 55 75 95 115 135 155 175 1.52 ± 1.59 ± 1.62 ± 1.61 ± 2.06 ± 2.27 ± 2.13 ± 2.24 ± 2.19 ± 2.72 ± 0.80 ± 8.85 ± 0.44 9.83 ± 0.49 10.17 ± 0.51 8.84 ± 0.44 10.62 ± 0.53 9.71 ± 0.49 11.42 ± 0.57 11.75 ± 0.59 10.72 ± 0.54 10.64 ± 0.53 2.40 ± 0.12 2.33 ± 0.12 2.29 ± 0.11 1.91 ± 0.10 1.90 ± 0.10 1.99 ± 0.10 1.98 ± 0.10 2.11 ± 0.11 2.08 ± 0.10 2.15 ± 0.11 1.89 ± 0.10 0.72 ± 0.04 10 ± 10 ± 10 ± 10 ± 10 ± 10 ± 10 ± 10 ± 10 ± 10 ± 1.900 ± 1.904 ± 1.668 ± 1.630 ± 1.782 ± 1.780 ± 1.887 ± 1.888 ± 1.904 ± 1.796 ± 1.024 1.082 1.015 0.955 1.096 1.075 1.163 1.181 1.148 1.140 0.384 0.120 ± 0.119 ± 0.115 ± 0.112 ± 0.108 ± 0.105 ± 0.105 ± 0.099 ± 0.097 ± 0.094 ± 2.72 ± 2.93 ± 2.80 ± 2.70 ± 2.99 ± 2.96 ± 3.16 ± 3.17 ± 3.15 ± 3.03 ± 0.08 0.08 0.08 0.08 0.10 0.11 0.11 0.11 0.11 0.14 0.04 0.072 0.074 0.065 0.063 0.069 0.069 0.073 0.073 0.074 0.070 ± 0.026 ± 0.028 ± 0.026 ± 0.028 ± 0.028 ± 0.032 ± 0.030 ± 0.030 ± 0.034 ± 0.034 ± 0.010 0.006 0.006 0.006 0.006 0.005 0.005 0.005 0.005 0.005 0.005 0.15 0.16 0.14 0.13 0.15 0.15 0.15 0.16 0.15 0.15 C.-R Liu et al Radiation Measurements 157 (2022) 106823 Fig The natural quartz ESR spectrum of several samples (S1, S4, S7, and S10) at low temperature (77K, liquid nitrogen) dissociation of Li, H associates (Poolton et al., 2000), rather than first changing their charge state (Weil, 1984) Thus, the intensity of Ti–Li center from 50 cm to cm increases (Fig 6), similar to that of Al center Compared with the Al and Ti–Li centers, the signal intensity of the Ti–H is very weak As shown in Fig 5c, the signal intensity of Ti–H center initially remains consistent at the depth of 180–130 cm, then increases to a maximum at 50 cm and decreases sharply with the in crease of baking temperature It is very interesting to compare Fig 5b and c that there is a good correspondence between the stage of rapid increase of natural signal intensity of the Ti–Li center and the stage of rapid decrease of natural signal intensity of the Ti–H center (40-0 cm) Poolton et al (2000) also observed this phenomenon by heating quartz samples before artificial irradiation and proposed the following explanation: beyond 870 ◦ C (temperature of the transition from β-quartz to β-tridymite), the Ti–H centers become unstable and dissociate, this would leave isolated Ti ions available for Li capture, and then enhance the Ti–Li center population At the stage where the natural signal intensity of ESR centers changes significantly (60-0 cm), compared with the change of less than one time of the Al center intensity, the signal intensity of the Ti–Li and Ti–H centers changed by a factor of and 2, respectively It indicates that the ESR intensity of the Ti center is more strongly dependent on the annealing history of the samples than the Al center (Poolton et al., 2000) As there are many potential sources of H+ and Li+ within the lattice in quartz, including water inclusions, OH molecules, [H3O4]0 defects, and cations associated with the Al or other centers (Halliburton et al., 1979; Nuttall and Weil, 1981; Yang and McKeever, 1990), the observed signal intensity change is much greater for Ti related signal centers than for Al center Compared with the signal intensity at the depth of 180–130 cm, the maximum intensity value of both Ti–Li and Ti–H center has been increased by two times and one time respectively (Fig 5b and c) Ac cording to the measurement results of dose rate (Table 1), we speculated that the irradiation sensitivity of both Ti–Li and Ti–H centers changed after high-temperature baking ESR intensity with irradiation for the six samples is shown in Fig Discussion In this study, the irradiation sensitivity is defined as the amount of signal growth per unit dose, that is: K = △E/△Gy Where K is the irradiation sensitivity constant, △E is the intensity of ESR signal growth after received irradiation of △Gy Recently, the Exponential + linear (EXP + LIN) function and Double saturating exponential (DSE) function have been recommended for dose response behavior fitting of the Al and Ti–Li centers, respectively (e.g Duval, 2012; Duval and Guilarte, 2015) But, in order to facilitate comparison and discussion, linear fitting is adopted in this study because the linear fitting is close to the exponential fitting in the low dose part, the maximum value of artificial irradiation is 2072 Gy in this study (Fig 6) The linear fitting equation is expressed as: I=K*(D + DE) Where I is the ESR intensity, D is the additional irradiation dose, DE is the equivalent dose The results of fitting see Table 5.1 The Al center According to the results of fitting (Table 2), the order of irradiation sensitivity constant of the Al center can be roughly expressed as KS8 = KS7 < KS5 < KS3 < KS2 = KS1(Fig 6a), indicating that the change of irradiation sensitivity of the Al center increases with the baking tem perature The Al center sensitivity of S7 is the same as that of S8, indi cating that the layer where S7 is located is not affected by baking or the baking temperature is not sufficient to change the irradiation sensitivity of the Al center As shown in Fig 5a, in the first stage (180-130 cm), the signal intensity of the Al center basically does not vary We interpret it as below 130 cm, the sediments were not affected by baking and the signal intensity of the Al center is the geological original intensity In the second stage (130-50 cm, between S7 and S3) the irradiation sensitivity of the Al center is increase, but the intensity of it decreases as the rise of baking temperature Therefore, it can be concluded that the signal in tensity of unbleachable part (during the deposition process) in Al center was released by the baking temperature at this stage, but the baking temperature was not sufficient to change the irradiation sensitivity of this center In the third stage (50-0 cm), the Al signal increases with decreasing depth, corresponding to the irradiation sensitivity of the Al 4.2 ESR measurement of irradiated aliquots According to the results of natural (non-irradiated) aliquots, we suggest that high-temperature baking may change the irradiation sensitivity of Al, Ti–Li, and Ti–H centers in quartz To verify this, we have conducted an artificial irradiation experiment for six samples (S1, S2, S3, S5, S7, and S8) to confirm whether the irradiation sensitivities of ESR centers actually change after baking by lava flow The growth of C.-R Liu et al Radiation Measurements 157 (2022) 106823 Fig Evolution of the signal intensity of ESR centers with accumulated gamma dose (a) Al center, (b) Ti–Li center, and (c) Ti–H center For Ti–H center, since the signal intensities of Sample S3 and S5 are much greater than the other four samples, two intensity axes were established to compare them together with the accumulated gamma dose S1, S2, S7, and S8 correspond to the left intensity axis and S3 and S5 correspond to the right intensity axis Fig Variation of signal intensity of ESR centers vs depth (a) Al center, (b) Ti–Li center, and (c) Ti–H center center increases with the baking temperature (Fig 6a) This suggests that high-temperature baking near to the lava flow is sufficient to alter the irradiation sensitivity of the Al center, and that the higher the temperature rises, the greater the sensitivity increases The Al center is a defect where an Al3+ replaces a Si4+ and is asso ciated with a monovalent cation M+, such as H+, Li+, or Na+ Because of C.-R Liu et al Radiation Measurements 157 (2022) 106823 Table The linear fitting results of quartz Al, Ti–Li, and Ti–H centers K = irradiation sensitivity constant; Adj r2 = goodness-of-fit Sample No S1 S2 S3 S5 S7 S8 Al center Ti–Li center Ti–H center K Adj.r2 K Adj.r2 K Adj.r2 0.6450 0.6498 0.5171 0.2951 0.1070 0.1188 0.9786 0.9811 0.9854 0.9531 0.9667 0.9730 0.5459 0.6079 0.3816 0.1778 0.0199 0.0182 0.9898 0.9906 0.9639 0.9783 0.9730 0.9760 0.0019 0.0029 0.0297 0.0438 0.0035 0.0035 0.9696 0.9667 0.9881 0.9642 0.9699 0.9838 the irradiation at room temperature, after trapping a hole, the cation M+ diffuses away Therefore, the increase of the Al center irradiation sensitivity observed with baking may be due to the diffusion of the cations within the quartz itself, and further studies are needed 5.2 The Ti center The order of irradiation sensitivity constant of the Ti–Li center can be expressed as KS8 = KS7