研究论文 正式出版 版本 4 Vol 9 (6) : 569-579 2018
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青藏高原东缘黄土石英光释光信号积分区间选择研究
Selection of integration time intervals for quartz OSL of loess in the Eastern Tibetan Plateau
: 2018 - 06 - 21
: 2018 - 09 - 20
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摘要&关键词
摘要:光释光信号积分区间的选择对等效剂量(De)的估算有重要影响。光释光衰减曲线并非单一的指数衰减,而由多个指数衰减函数组成,且每个衰减函数代表不同的信号组分。因矿物晶格陷阱类型不同,各组分有不同的衰减率、热稳定性等。本文对采自青藏高原东缘4个典型黄土分布区的黄土样品进行了系统的石英光释光组分分析和背景区间扣除研究。结果发现:(1)高原东缘黄土石英光释光信号由快、中、慢组分组成,并以快组分占主导,适合用单片再生剂量法测定等效剂量;(2)不同背景区间扣除对小于10 Gy样品等效剂量结果影响较小,误差范围内一致;(3)对大于10 Gy样品,选取早、晚不同背景区间扣除其等效剂量结果差异显著,两者差值占晚期背景扣除所得De值的10%—38%,且有随De值增加而增大的趋势,因此计算大于10 Gy样品De时应慎重选择积分区间。
关键词:光释光信号组分;背景扣除;石英光释光;黄土;青藏高原
Abstract & Keywords
Abstract: Background, aim, and scope Selections of the integration time intervals for the quartz OSL is very important for estimating equivalent dose (De). The traditional method, in calculating De, is to select the first few seconds of OSL decay curve as the initial interval and subtract the last few seconds of decay curve as the background subtraction (e.g. 0—0.4 s, 19.9—24.9 s). In 2010, Cunningham and Wallinga suggested that the early background subtraction should be used in standard protocol. That is to select the first few seconds of OSL decay curve as the initial interval and subtract its followed few seconds interval as the background subtraction (e.g. 0—0.4 s, 0.4—1.4 s). Some recent studies also indicated the differences exist between De values by using ‘early background’ and ‘late background’. To further illustrate the effect of different background interval subtractions on the equivalent dose, we have systematically studied loess samples collected from the four typical loess distribution areas in the eastern margin of the Qinghai- Plateau. Materials and methods OSL samples were collected from 4 typical loess profiles using steel pipes, ~25 cm long and ~4 cm in diameter. Extraction of the quartz from samples and the OSL measurements were performed in the red light darkroom in the OSL laboratory of Chengdu Institute of Mountain Hazards and Environment, Chinese Academy of Sciences. First, the outside parts of sample, about 3—5 cm, were removed. After that, the 10% HCL and 30% H2O2 were added in the residual samples to remove carbonates and organics. Next, the 38-63μm of quartz components was extracted for measuring De. After De of all samples were measured with the single aliquot regenerative-dose (SAR), we analyzed the components of quartz OSL signals of all samples and selection of integration time intervals using Analyst 4.53. Result The proportions of fast component of all samples are above 84%. For those samples of <10 Gy, the difference of average De between A1 (0—0.4 s, 0.4—1.4 s) and A2 (0—0.4 s, 19.9—24.9 s) is only 0.00—0.32 Gy, which is 0—5% for the average De of A2. Compared to <10 Gy samples, to >10 Gy samples, the difference is 16.33—56.17 Gy, which is 10%—38% for the average De of A2. Discussion For those samples with >10 Gy, we analyzed the changes of their natural and test dose signals after selecting the different background intervals to subtract. We found that the average rate of change of natural signals is 13%—22% after selecting the different background intervals to subtract, and the average rate of change of test dose signals is 17%—31%. The difference of average rate of change of the two is 4%—15%. Thus, we infer that it may be caused by the large difference of average De between A1 and A2 for >10 Gy samples. The further component analysis of test dose shows that a significant proportion of unstable medium components are included in test dose signals, so resulting in a higher De when calculated with the early background subtraction (0—0.4 s, 0.4—1.4 s). Conclusions The fast component is the dominant signal of quartz OSL signals of loess in the eastern margin of Qinghai-Tibet Plateau, and the equivalent dose can be measured using the SAR procedure. The effect of different background intervals subtraction on De results of <10 Gy samples is small, and the error range can be negligible. But for >10 Gy samples, the effect is significant. It also shows that the difference of De between A1 and A2 seems to be increasing with the increase of the equivalent dose. Recommendations and perspectives The integral intervals should be carefully selected when calculating De of >10 Gy samples. To calculate OSL age of those samples, further studies are needed for selecting a more appropriate method of background subtractions, such as using independent age control or comparing to the result of measuring fast component only.
Keywords: components of OSL signals; background subtraction; quartz OSL; loess; Tibetan Plateau
光释光(OSL)测年技术自1985年(Huntley et al,1985)被提出以来,因其测试矿物易得、有效测年范围广等优点被广泛应用于第四纪沉积物定年研究(如:Lai,2008;Buylaert et al,2009;Li and Li,2012;Lai and Fan 2014;Kang et al,2016;Wintle and Adamiec,2017)。Murray and Wintle(2000)对单片再生剂量法(single aliquot regenerative-dose,SAR)的改进大大提高了光释光测年的准确度和精确度,因而被广泛应用于风成黄土的精细测年研究(Kang et al,2015,2016;Guérin et al,2017;Song et al,2018)。
应用SAR法测定沉积样品等效剂量(De)的基本前提之一,就是样品中石英光释光信号以快组分为主(Wintle and Murray,2006),通过初始信号扣除背景值可得到净释光信号(Galbraith and Roberts,2012;Wallinga and Cunningham,2015)。Huntley et al(1985)首次测试光释光信号时发现:恒定激发(continuous wave OSL,CW-OSL)时,光释光信号以非单一指数递减。此后的研究发现:光释光衰减曲线由衰减率、热稳定性及剂量响应特征等不同的快、中、慢组分组成(Smith and Rhodes,1994;Bailey,1997;Jain et al,2003;Bailey,2010),并认为其原因是石英矿物晶格中存在不同的深度陷阱和重组中心(Bailey,1997)。相关研究表明:快组分占主导时,样品光释光信号晒褪更完全,热转移更小,测试的年代更稳定(Wintle and Murray,2006;Wintle,2010)。因此,为了减小年代结果误差,计算等效剂量时应使快组分信号所占比例尽可能大。
计算等效剂量时,通常会选取光释光衰减曲线前几秒作为初始信号区间减去最后几秒区间信号作为背景扣除(Banerjee et al,2000),但这种方法存在释光信号中不稳定的中组分和慢组分未被充分扣除,可能造成年代结果低估的现象,尤其是年代较老的样品(Murray et al,2008)。因此,近年来有研究者提出通过早期背景扣除法计算De值,即把光释光衰减信号的前数个通道积分作为初始信号,相邻的数个通道积分作为背景信号(Ballarini et al,2007;Cunningham and Wallinga,2010)。不同沉积类型样品的等效剂量(De)值对信号区间选择方式的敏感度不同(Cunningham and Wallinga,2010)。Costas et al(2012)研究北海南部海岸沙丘年代时,将样品光释光信号不同背景区间扣除后的年代结果与独立年代控制比较发现:早期背景扣除后得到的释光年代结果更接近独立年代。腾格里沙漠南缘风成沉积物快组分光释光信号选择研究表明:等效剂量对信号区间选择方式较为敏感(彭俊和韩凤清,2013)。
青藏高原东缘广泛存在的风成黄土是该区晚更新世环境变化的良好记录,详细的光释光测年研究是建立高原黄土年代框架和深入理解高原东部环境演化的重要基础。本文对采自青藏高原东缘4个典型黄土分布区的黄土样品进行系统的石英光释光组分分析和背景区间扣除研究,进一步探讨不同背景区间扣除对风成黄土石英光释光等效剂量的影响,为今后高原东缘黄土光释光等效剂量的分析,进而建立可靠的光释光年代序列提供依据。
1   样品采集及实验过程
1.1   样品采集及前处理
选择高原东缘黄土分布较集中的甘孜、小金、马尔康及舟曲4个地区(图1),开展系统的石英光释光测年研究。光释光样品采集时按照光释光采样的通用方法,先开挖探槽,将剖面表层风化部分去除,再将不锈钢管垂直打入剖面,然后取出钢管,避光封装和保存。本研究共采集黄土光释光样品11个。


图1   研究区地形和采样地点
Fig.1 Geography and sampling sites in the study area
实验分析时,将采集的光释光样品在红光暗室中拆开,去除两端3—5 cm可能曝光的部分,将剩余中间部分进行前处理。粒度分析发现:该区黄土主要由黏土和粉砂组成,众数粒径主要集中于35—63 μm,粗组分含量较少,不能提供足够的纯石英样品。因此,选择了筛取粒径38—63 μm的组分进行提纯(Lai et al,2010;Chen et al,2017)。样品前处理时,先通过盐酸和双氧水去除样品中的碳酸盐和有机质,再使用35%氟硅酸浸泡,去除长石,然后加入稀盐酸去除氟化物沉淀,最后用磁性粒子去除磁性矿物,获得提纯后的石英样品(赖忠平和欧先交,2013)。提纯后的石英样品,需使用波长850 nm的红外激发光源(IRSL)对其进行检测,确保样品中长石信号已基本去除或处于较低水平,避免影响等效剂量的结果(Lai and Brückner,2008)。本次实验所有样品IRSL检测结果表明:长石红外释光信号与石英光释光信号比值小于10%,说明长石信号已基本被去除干净(Duller,2003),可以用来测定等效剂量。
1.2   等效剂量测试
所有样品的等效剂量在中国科学院、水利部成都山地灾害与环境研究所光释光实验室完成测试。等效剂量测试使用全新模块化的德国lexsyg research 全自动TL/OSL 测量仪测定(Richter et al,2013),测试程序使用Murray and Wintle(2000)改进的单片再生剂量法。
为选择合适的预热温度,进行了预热坪实验分析。首先,将预热温度从180℃间隔20℃增加到300℃,结果显示,在低温区(180—220℃)预热坪检验结果误差较大,而在240—260℃样品等效剂量较稳定(图2a)。为检测该地区样品是否适合使用单片法(SAR)进行等效剂量测试,进行了剂量恢复实验(Murray and Wintle,2003),结果显示(图2b),在240—260℃剂量恢复比率最接近1。因此,选择260℃,保持10 s作为天然信号和再生剂量的预热温度,220℃作为实验剂量的预热温度,具体测试流程见表1。


图2   样品ZQ-5预热坪实验(a)、剂量恢复实验(b)测试结果
Fig.2 Result of preheating plateau and dose recovery of sample ZQ-5
表1   SAR测试基本流程(Murray and Wintle,2000)
步骤
Step
实验过程
Procedures
释光信号
OSL signals
1预热,5℃/s至260℃,保持10 s
Preheat, 5℃/s to 260℃, keep 10 s
TL
2加热,5℃/s至125℃保持90 s,蓝光激发70 s
Heat, 5℃/s to 125℃ keep 90 s, blue stimulate 70 s
Ln, Li (i=1, 2, …, 6)
3辐照试验剂量(TD)
Irradiation test dose (TD)
4预热,5℃/s至220℃
Preheat, 5℃/s to 220℃
TL
5加热,5℃/s至125℃保持90 s,蓝光激发70 s
Heat, 5℃/s to 125℃ keep 90 s, blue stimulate 70 s
Tn, Ti (i=1, 2, …, 6)
6依次辐照再生剂量Ri(i=1,2,…,6),重复1—6次
Sequential irradiation regeneration Ri (i=1, 2, …, 6), repeat 1—6 times
测定等效剂量时,先将样品均匀单层涂在直径约1 cm测片上,125℃温度条件下,用强度50 mW∙cm−2、波长(458±5) nm的蓝光激发70 s。随后,释光信号经厚2.5 mm的滤光镜Hoya U340及厚5 mm的干涉滤光片Delta BP365/50 EX进入9235QB光电倍增管进行记录,实验剂量及再生剂量辐照源选择(90Sr/90Y)β源。11个黄土样品共测得100个测片(表2),图3 a—h分别显示了部分样品的衰减曲线及生长曲线。


图3   样品XJ-2、ZQ-5、ML-1及XS15-4衰减曲线(a、c、e、g)和生长曲线(b、d、f、h)
Fig.3 Decay curves (a, c, e, g) and grow curves (b, d, f, h) of sample XJ-2, ZQ-5, ML-1and XS15-4
2   释光衰减曲线组分分析
2.1   衰减曲线组分拟合原理
光释光衰减曲线并非单一指数衰减,而是衰减率不同的指数函数之和,且每个函数代表不同的释光组分(Smith and Rhodes,1994)。Bailey et al(1997)将其分别称为快、中、慢组分。他们认为,恒定激发(CW-OSL)下,释光衰减曲线非单一指数递减是由于石英晶格中存在多个不同类型的陷阱。这些陷阱使晶体产生局域能量态,提供额外的热、光等能量时,价带中的电子吸收能量向导带移动成为自由电子,这些获得能量的电子从价带逃逸后在其形成离位电子和空穴。再一次受到激发后,陷阱中的电子和发光中心复合释放光子。整个过程,各电子速率不同。来自快组分和中组分的电子以不同速率会优先在释光中心重组(Bailey,2001;Jain et al,2003;Bailey,2010;Wintle and Adamiec,2017)。
2.2   衰减曲线组分拟合
据前人研究成果,CW-OSL衰减曲线可由三个指数衰减组分拟合(Cunningham and Wallinga,2009)。为便于对比,利用Analyst 4.53软件分别对样品ZQ-2和ZQ-5一个测片的天然信号进行了前6 s的组分拟合。拟合公式为公式(1),拟合结果见图4。因室温短期测量时,慢组分以恒定低速率衰减(Bailey et al,1997),故图4中将常量与慢组分进行了合并。即背景+慢组分表示公式中a值和n3×b3e-b3t 之和,图4c、d残留信号表示测量值与拟合值之差。
y=a+[n1×b1e-b1t ] +[n2×b2e-b2t ]+[n3×b3e-b3t ] (1)
式中:a是常量;bi表示去除陷阱可能性大小,即去陷概率(detrapping probability),大小由光电离截面(photoionization cross-section)和激发光强度(I0)决定;ni表示矿物晶格捕获电子数(i=1,2,3)。


图4   样品ZQ-2(a、c)及ZQ-5(b、d)组分拟合及误差图
Fig.4 Fitting of component and the error of sample ZQ-2 (a, c) and ZQ-5 (b, d)
图4a、图4b显示,样品ZQ-2和ZQ-5总信号在激发前2 s已降到本底,表明这两个样品晒褪完全且以快速衰减为主,进一步说明青藏高原东缘黄土可用单片再生法测定等效剂量。再者,如图中所示,快、中、慢组分对总信号贡献不同,各组分衰减率也存在较大差异。图4c、图4d中可以看出,样品ZQ-2和ZQ-5测量值与拟合值之差基本在0值左右(注意纵坐标数值变化),表明无论样品ZQ-2还是样品ZQ-5释光信号衰减曲线都可以利用公式(1)得到很好的拟合效果,说明将样品分为快、中、慢组分是合适的。
为进一步讨论各组分初始信号与总信号的关系,计算了11个样品所有测片在t=0时,各组分对总信号的占比,结果见表2。
表2   所有样品各组分初始信号占总信号百分比
样品号快组分占比中组分占比背景+慢组分占比SAR测片个数
Sample IDThe percentage of fast componentThe percentage of medium componentThe percentage of BG+slow componentThe number of SAR aliquots
/%/%/%
XJ-18513.81.29
XJ-289.990.710
ZQ-284.81419
ZQ-591.57.21.49
ZQ-688.810.20.99
ZQ-887.611.11.39
ML-187.212.30.49
ML-492.67.20.310
ML-591.97.80.310
XS15-489.99.40.78
XS15-590.590.58
合计 Total100
为减小误差,计算了每个样品所有测片各组分t=0时信号占总信号的比例,并求其均值。样品XJ-1初始时刻快组分信号占总信号的85%,是其9个SAR测片快组分占比的平均值,以此类推。表2中显示,同一样品快、中及背景+慢组分在t=0时信号占总信号百分比差异显著,且依次递减,这可能与各组分来源不同有关(Bailey et al,1997)。再者,不同样品各组分信号占总信号百分比也存在差异,推测可能因为每个样品矿物晶体本身缺陷不同所致(Bailey et al,1997;Wintle and Adamiec,2017)。但总体来看,高原东缘黄土石英OSL快组分在t=0时信号占总信号百分比均在84%以上,说明青藏高原东缘黄土石英光释光信号以快组分占主导。
3   不同背景信号扣除区间对等效剂量的影响
研究表明:背景信号扣除区间为初始信号区间2—3倍时,快组分分量占总信号比例最大(Cunningham and Wallinga,2010)。据此,对所有样品的测片进行了背景扣除区间选择分析(表3,图5)。表3 中,A1组平均De值由每个样品单个测片选取前0—0.4 s光释光信号减去其随后0.4—1.4 s光释光信号后,利用指数或指数加线性对释光信号进行拟合,形成单个测片生长曲线,再将校正后的光释光信号强度内插到生长曲线,得到该测片等效剂量,最后计算所有测片等效剂量均值。同理,得到所有样品A2组平均De值。但需注意,A2组最终拟合的光释光信号是0—0.4 s释光信号减去19.9—24.9 s光释光信号后所得。表中差值表示A1组和A2组平均De值之差。图5中,虚线表示早、晚期背景扣除后所得等效剂量相等(图中1∶1线),实线为所有样品早、晚期背景扣除后所得等效剂量线性回归结果(k=0.81)。
表3   所有样品不同积分区间等效剂量比较
样品号

Sample ID
A1组平均De值
The mean De of A1 group
/Gy
A1组平均误差
The mean error of A1 group
/Gy
A2组平均De值
The mean De of A2 group
/Gy
A2组平均误差
The mean error of A2 group
/Gy
差值
Deffience
/Gy
差值/A2组平均De
Deffience/mean De of A2 group /%
SAR测片个数
The number of SAR aliquots
XJ-11.30.021.30.03009
XJ-25.630.055.640.050.0109
ZQ-27.180.216.850.20.3258
ZQ-571.172.0854.841.8216.33308
ZQ-697.285.7676.424.5720.86278
ZQ-8137.674.32107.353.0930.32288
ML-1124.932.67112.61.612.33119
ML-4189.56.01172.485.4917.02109
ML-5202.688.71146.514.1256.173810
XS15-4211.155.57161.185.9549.96318
XS15-5311.0412.33258.037.7253.01218
合计 Total94
表3和图5中可以看到,所选初始信号区间相同时,不同背景扣除区间对<10 Gy样品(XJ-1、XJ-2、ZQ-2)和>10 Gy样品(ZQ-5、ZQ-6、ZQ-8等)等效剂量结果差别显著。对于<10 Gy样品,A1组与A2组平均De差值只有0.00—0.32 Gy,两者之差占A2组平均De比例在0—5%,误差范围内可忽略不计。图5中也可以看出,样品的等效剂量越小(<10 Gy)线性回归结果与1∶1线越接近。<10 Gy样品ZQ-2辐射径向图(图6a、图6b)也显示,该样品不同背景区间扣除前后除等效剂量(单位:s)基本无变化外,其离散度(Galbraith et al,1999)也变化较小。这与Cunningham and Wallinga(2010)所得结论略有不同,可能与样品类型及是否完全晒褪有关。


图5   所有样品早期背景扣除及晚期背景扣除所得De比较
Fig.5 Comparison of De of early background subtraction and late background subtraction for all samples
与<10 Gy样品不同,>10 Gy样品不同背景区间扣除前后等效剂量有明显差异(表3和图5)。表3中,>10 Gy样品A1组与A2组平均De差值最小为16.33 Gy,最大可达56.17 Gy,且所有样品A1组平均De值均大于A2组,两者差值占A2组平均De值比例可达10%—38%。若以中国黄土2—5 Gy/ka的环境剂量率(张克旗等,2015)计算,A1组与A2组释光年代最小相差3—10 ka,最大可达8—28 ka。图5可知,随着样品等效剂量的逐渐增加,线性回归结果逐渐偏离1∶1线,这说明随着等效剂量的增加,早、晚期不同背景扣除后得到的等效剂量结果差异逐渐增大。此外,辐射径向图(图6a、图6b)显示,不同背景区间扣除前后>10 Gy样品ZQ-5等效剂量相差约158 s(19 Gy)左右。虽然两组离散度都在20%以内(Galbraith et al,1999;Arnold and Roberts,2009),但早期背景扣除(A1组)(5.3%±1.0%)明显优于晚期背景扣除(A2组)(9.1%±1.0%)。


图6   样品ZQ-2和ZQ-5早期背景扣除(a、c)与晚期背景扣除(b、d)辐射径向图
Fig.6 Sample ZQ-2 and ZQ-5 early background subtraction and late background subtraction radial diagram
表4   所有>10 Gy样品不同背景区间扣除天然信号和实验剂量信号的变化
样品号
Sample ID
A1组平均
(OSLN-BGN)/OSLN
A1 group mean (OSLN-BGN)/OSLN
/%
A2组平均
(OSLN-BGN)/OSLN
A2 group mean
(OSLN-BGN)/OSLN
%
A1组平均
(OSLTD-BGTD)/OSLTD
A1 group mean (OSLTD-BGTD)/OSLTD
%
A2组平均
(OSLTD-BGTD)/OSLTD
A2 group mean (OSLTD-BGTD)/OSLTD
%
平均变化率N
Ratio of mean change N
%
平均变化率TD
Ratio of mean change TD
%
A1组平均Ln/Tn
A1 group mean Ln/Tn
A2组平均Ln/Tn
A2 group mean Ln/Tn
测片个数
The number of SAR aliquots
ZQ-58298639316314.653.628
ZQ-68399709515255.214.538
ZQ-88398699416265.935.128
ML-17799719722275.224.899
ML-486100819814185.715.419
ML-586100819813176.065.8010
XS15-48099699619276.535.808
XS15-58099739720246.846.418
OSLN:样品天然信号;BGN:测量天然信号时的背景信号;OSLTD:样品实验剂量信号;BGTD:测量实验剂量信号时的背景信号。
OSLN: The natural signals of samples; BGN: The background signals of measuring natural signals; OSLTD: The test dose signals of samples; BGTD: The background signals of measuring test dose.
等效剂量由校正后的天然释光强度(Ln/Tn)内插到生长曲线所得。为讨论>10 Gy样品等效剂量不同背景区间扣除前后差异显著的原因,对样品天然信号及实验剂量信号进行了分析。表4显示,>10 Gy样品的天然释光信号在A1与A2组背景区间扣除后,剩余天然信号占总天然信号比例变化了13%—22%,实验剂量不同背景区间扣除后的释光信号占总信号比例的变化可达17%—31%,两者平均变化率相差4%—15%。因此,推测>10 Gy样品等效剂量不同背景区间扣除前后差异显著,主要由样品天然信号与实验剂量信号不同背景区间扣除前后变化率不一致,导致A1组平均Ln/Tn均大于A2组所致。然而,对于>10 Gy的样品最终应选择哪种背景扣除方式进行年代计算,还需要进一步研究。
为进一步分析原因,以样品ZQ-5为例对>10 Gy样品天然信号组分和实验剂量信号组分进行了分析(图7)。如图所示,样品ZQ-5天然信号的快组分与总信号比值在0.9左右,中组分与总信号比值基本在0.1以下,背景+慢组分则在0值附近,说明ZQ-5天然信号以快组分占主导,这与前面结论一致。与天然信号各组分分布不同,ZQ-5实验剂量信号的快组分与总信号比值只有0.8左右,甚至低至0.7(位置3),中组分所占比值平均在0.15以上,最高可达0.2以上,背景+慢组分所占比值也均高于天然信号。这说明选取0—0.4 s作为初始信号时,实验剂量信号中包含了相当比例的不稳定中组分信号,这与Steffen et al(2009)利用天然信号比再生剂量信号(N/R)分析的结论一致。


图7   样品ZQ-5各测片不同组分占总信号比值
Fig.7 Ratio of the different components of sample ZQ-5 to the total signal
FN、MN、(S+BG)N:天然信号快、中、背景+慢组分与总信号比值;FT、MT、(S+BG)T:实验剂量信号快、中、背景+慢组分信号与总信号比值。FN, MN, (S+BG)N: Ratio of fast, medium, background + slow component to the sum of component for natural signals; FT, MT, (S+BG)T: Ratio of fast, medium, background + slow component to the sum of component for test dose signals.
FN、MN、(S+BG)N:天然信号快、中、背景+慢组分与总信号比值;FT、MT、(S+BG)T:实验剂量信号快、中、背景+慢组分信号与总信号比值。
FN, MN, (S+BG)N: Ratio of fast, medium, background + slow component to the sum of component for natural signals; FT, MT, (S+BG)T: Ratio of fast, medium, background + slow component to the sum of component for test dose signals.
4   结论
通过上述对青藏高原东缘典型风成黄土样品的石英光释光信号组分分析和不同背景区间扣除选择的详细分析,可获得如下主要结论:
(1)石英光释光信号组分分析表明:高原东缘黄土石英光释光信号由衰减率、稳定性等不同的快、中、慢组分拟合而成,但以快组分占主导,所有分析样品快组分占总信号比例均在84%以上,适合用单片再生法测定其等效剂量。
(2)对高原东缘黄土石英光释光信号进行不同背景区间扣除分析表明:不同背景扣除方式对于小于10 Gy样品等效剂量计算的影响较小,误差范围内一致,离散度也无明显变化;。对于大于10 Gy样品选取不同背景区间扣除后,其等效剂量差异显著,最小相差16.33 Gy,最大达56.17 Gy,且均为早期背景扣除获得的等效剂量(De)大于晚期背景扣除,离散度前者也优于后者。
致谢:
感谢审稿人的意见和建议,王姣姣、黄政、洪苗苗参加了野外工作,特此致谢!
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稿件与作者信息
刘楠楠1, 2
LIU Nannan1, 2
杨胜利1*
YANG Shengli1*
杨胜利,Email: shlyang@lzu.edu.cn
刘维明2
LIU Weiming2,
成婷1
CHENG Ting1
陈慧1
CHEN Hui1
唐国乾1
TANG Guoqian1,
李 帅1
LI Shuai1
梁敏豪1
LIANG Minhao1
国家自然科学基金项目(41472147);兰州大学中央高校基本科研业务费专项资金(lzujbky-2017-ct05,lzujbky-2015-k10);兰州大学西部环境教育部重点实验室开放基金
National Natural Science Foundation of China (41472147); Fundamental Research Funds for the Central Universities (lzujbky-2017-ct05, lzujbky-2015-k10); Open Foundation of MOE Key Laboratory of Western China’s Environmental System, Lanzhou University
出版历史
出版时间: 2018年9月20日 (版本4
参考文献列表中查看
地球环境学报
Journal of Earth Environment