摘要
用 3 H作为示踪剂研究水的运动是一种最常用的方法。本文通过3 H在天然黄土包气带的现场示踪试验 ,得到了3 H在非饱和黄土中迁移的某些特征。天然条件下现场示踪试验在 A、B两个试验坑进行。A、B坑的面积均为 2× 2 m2 ,深度分别为 30 cm和 10 0 cm。3 H示踪核素与一定量黄土均匀混合 ,制成示踪源 ,铺设于坑底中央 ,示踪源层的厚度为 0 .7cm,面积 1.5× 1.5m2 ,源层上方用原土回填。在 1989年 5月～ 1991年 7月试验期间 ,定期从两坑中采集土芯样 ,并切割成 0 .5～ 1cm厚的土壤样品 ,用真空加热蒸馏法 ,分离出土壤水 ,用液体闪烁计数器测量土壤水中的3 H含量 ,得到土壤中 3 H的浓度分布。结果发现 ,在非饱和黄土中 ,3 H浓度分布的质心位置 X0 (t)总体上是向下运动的 ,而且 ,随着深度的增加 ,3 H向下迁移速度变慢 ;试验期间 ,3 H在埋深 30 cm的 A坑中向下迁移速度为 5.4× 10 -2 cm/ d,在埋深 10 0 cm的 B坑为 1.6× 10 -2 cm/ d。但是 ,与 A坑相比 ,B坑中 3 H的质心位置上下迁移明显。另外 ,根据拟合结果可以看出 ,3 H的垂向浓度分布方差σ2x(t)随取样时间 t的变化关系近似呈 S型 ,对 A。
It is one of the common methods to study water movement in geological media using 3H as tracer. Some characteristics of migration of 3H in aerated loess were obtained through analyzing the results of the field tracer migration tests of 3H under natural rainfall condition. The tests were conducted in test pits A and B. Area of each test pit is 2×2 m 2. The depth of test pits A and B is 30 and 100 cm, respectively. Tracer 3H was mixed with an amount of loess to prepare a tracer source. The tracer source was put at the center of bottom of test pits A and B. The thickness and area of the tracer source layers were 0.7 cm and 1.5 ×1.5 m 2, respectively. The tracer source layers were covered by original loess to level surface. Soil cores were periodically collected from test pits A and B from May 1989 to July 1991. The soil cores were cut into samples with thickness of 0.5~1.0 cm. The samples were heated and distilled under vacuum condition in order to separate water from loess. 3H content in the water samples was measured with low level liquid scintillation analyzer to obtain concentration distributions of 3H in loess. It is found from the fitted results that the positions of the center of mass, X 0(t), of concentration distributions of 3H moved down as a whole in loess aerated zone during the tests. Migration velocity of the mass center of the concentration distribution of 3H decreases with depth. During the test down moving velocities of 3H were 5.4×10 -2 cm/d (at depth of 30 cm in test pit A) and 1.6×10 -2 cm/d (at depth of 100 cm in test pit B), respectively. Compared with the results in test pit A, the positions of the mass center of concentration distribution of 3H in test pit B moved up and down obviously. It can be seen from the fitted results that the longitudinal distribution variance of 3H,σ 2 x(t) shows S shape with sampling time, t. And the longitudinal distribution variance of 3H,σ 2 x(t), can be expressed in different equation for different intervals. (
出处
《辐射防护》
CAS
CSCD
北大核心
2000年第1期57-61,共5页
Radiation Protection
关键词
现场示踪试验
黄土包气带
氢示踪剂
核素迁移
H,Field Tracer Migration Test,Migration,Loess Aerated Zone, Concentration Distribution Variance
