| 第四纪年龄测定的新技术──热电高质谱铀系法的发展近况 |
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| 引用本文： | 彭子成.第四纪年龄测定的新技术──热电高质谱铀系法的发展近况[J].第四纪研究,1997,17(3):258-264. |
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| 作者姓名： | 彭子成 |
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| 作者单位： | 中国科学技术大学地球和空间科学系 合肥 230026 |
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| 基金项目： | 中国科学院资源与生态环境研究资助 |
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| 摘 要： | 近10年来国际上用热电离质谱代替α谱仪测定不平衡铀系样品的年龄，在造礁珊瑚、洞穴堆积物、年轻火山岩和湖泊沉积物等领域已取得了显著的成果。该技术有明显的优点，如样品用量少，测试时间短，测量精度高，测年范围宽，是中更新世至全新世以来有效的测年方法之一，可为全球变化研究提供高精度和高灵敏度的年龄谱，展示了热电离质谱技术如同加速器质谱技术一样，有广阔的应用前景。我们曾用MAT－262质谱仪对国内石笋标样(GBW04412，GBW04413)和国际珊瑚标样(RKM－4)进行过测试，取得了与标准值一致的结果。
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| 关 键 词： | 热电离质谱技术 高精度定年的意义 |
| 收稿时间： | 1997-05-14 |
| 修稿时间： | 1997-05-31 |
NEW TECHNIQUE OF THE DATING QUATERNARY MATERIALS: THE DEVELOPMENT OF THE THERMAL IONIZATION MASS SPECTROMETRY-U SERIES METHOD |
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| Institution: | Department of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026 |
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| Abstract: | A new method of mass spectrometry, i. e. thermal ionization mass spectrometry （TIMS） for uranium series, has replaced alpha spectrometry, improving in greatly dating geological samples and tracing geological processes. In 1986 and 1987,Edwards et al.2,3] and Chen et al.4] first reported their data of the TIMS dating for the coral. Samples from different sites. The experiments show that TIMS is superior to alpha spectrometry in terms of the following aspects: （1） less amounts of samples,3-5g for samples younger than 1 000 years and only several hundred mg for samples older than 10 000 years; （2） short testing time, about 3 hours for uranium or thorium,（3） high measurement precision, 1%-3% for 1 000-10 000 years, < 1% for 10 000-200 000 years; （4）broad dating scope, from 100 years to 500 000 years. The high precision of the results enables us to identify geological and environmental changes at shorter intervals. Therefore, TIMS, like accelerator mass spectrometry, is of a promising future.Recently, TIMS has been employed to determine the ratio and content of various isotopes. However, direct determination of the daughters of uranium series through TIMS did not witness initial results until the mid 80s. The reason for this is that thecontent of the daughter nuclides, such as 230Th, is low, 2 × 108 atoms / g in corals for 100 years and 1 × 1011 atoms / g for 120 000 years. In order to obtain the high precision measurement of these subtypes, it should be necessary to achieve high ionization efficiency and high abundance sensitivity of mass spectrometry. In October,1996, we introduced a MAT-262 mass spectrometer from Finnigan MAT Company.The equivalent curvature radius of the equipment is 64 cm. It has 7 Faradny-Cup receptors, 1 ion counter, and RPQ with ion counter system. This meter, one of the most advanced commercial thermal ionization mass spectrometers, counts dark current ion at 0.6 ion / minute and ion current ranged in 10-19 - 10-10 A with abundance sensitivity 6 × 10-9.With the aid of MAT-262 mass spectrometer, we have tested the domestic stalagmite standard samples （GBW04412, GBW04413） and the intemational coral standard sample （RKM-4）. Our results are consistent with standard values.TIMS method can be used in study of reef coral. The results of TIMS dating show that the rise of sea level during the last interglacial period was influenced not only by sunshine intensity but also by some other dynamic factors.Cave deposits, such as stalagmite and flowstone, have obvious sedimentary annual rings recorded information of paloeclimatological changes. TIMS method is used to study the cave accumulation. The findings indicate that the change in sunshine radiation intensity is not the only factor responsible for ice melting, which is consistent with TIMS study on coral. TIMS method can be employed to date young volcanic rock and to promote U/ Th geochemistry. TIMS will benefit the researches on the chronology of volcanic rock and periodical cycles of the eruption in Tengchong, Changbai shan Mountain and Wudalianchi. Since lake sediments have stored a great deal of paleoclimatological information, they become one of the important objects in Global Change strategy study.Hydrogenous thorium in the lake sediments is strongly influence of the TIMS dating results appeared in a positive errors.In a word, TIMS has witnessed its successful applications in the studies of coral,cave sediments, young volcanic rock, and lake sediments. Oretically, TIMS uranium series can be widely utilized in studies of underground water, continental surface sediments （for example, soil）, sulfate, and apatite sediments, and in marine chemistry and archaeology （bone and tooth fossils）. ms method will promote the development of Quaternary sciences. |
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| Keywords: | thermal ionization mass spectrometry(TIMS) technique high precise dating significance |
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