海相年轻沉积物36Cl定年研究
36Cl Dating of the Young Marine Sediments
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摘要: 提取、纯化海相沉积颗粒表面 "诱导吸附"的36Cl(和Cl),制成加速器质谱(AMS)测定放射性比度I (36Cl/Cl)所需的标样,即高纯度AgCl;定量计算出沉积颗粒沉积封闭时的放射性比度I0 (36Cl/Cl),依据放射性衰败定律I=I0e-λt计算得到沉积年龄t。研究结果表明:年轻的海相沉积物沉积封闭时的36Cl放射性比度I0与地理纬度之间存在线性关系,采取具有代表性、无污染的太平洋表面海水(4°18'N,161°09'E),经AMS测出的36Cl放射性比度为IL为99.34±10.30,再利用 36Cl产率与纬度的关系图,得出"放射性比度-产率"的比例常数μ为23.65238。并测定了两个海底沉积物和一个海底锰结核的放射性比度I,计算得到的沉积年龄分别为83.2×104 a、74.0×104 a、17.6×104 a。提出I0的定值计算方法具有科学依据,可操作性强,为揭示海洋沉积地层相关关系和沉积年龄精确测定提供技术支撑。Abstract: Accelerate mass spectrometry (AMS) has been used to the measurement of specific activity I ( 36Cl/Cl) of high purity AgCl made of "inducing-adsorbed" 36Cl (and Cl) collected and purified from the surface of young marine sediments. Sediment age t was calculated from closed specific activity I0 ( 36Cl/Cl) of sediment grain based on the radioactive decay law I=I0e-λt. The study shows that the specific activity I0 of closed 36Cl in earlier marine sediments has linear relationship with latitude. 36Cl specific activity IL from typical and uncontaminated seawater of the Pacific Ocean (4°18'N,161°09'E) surface was measured by AMS and the result was 99.34±10.30. And taking account of latitude factor, the proportionality constant of specific activity-yield (μ) was obtained as 23.65238. 36Cl specific activity of two sediments grains and a manganese nodule from seabed has measured and the ages of sedimentation for the samples are 83.2×104 a, 74.0×104 a, and 17.6×104 a respectively. The calculation method of I0 is of scientific foundation and accessibility and it can provide the exact sedimentation ages and explain the correlation of marine sediment layers.
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