黄土包气带中核素二维迁移的试验研究

EXPERIMENTAL INVESTIGATION OF TWO DIMENSION MIGRATION OF RADIONUCLIDES IN LOESS AERATED ZONE

为了研究黄土包气带中放射性核素在垂直和水平方向上的二维迁移 ,在野外试验场的 C坑 (天然条件 )和 F坑 (人工喷淋条件 )进行了取样测量。将 85Sr、13 4Cs和 60 Co三种核素与黄土均匀混合 ,制成示踪源 ,埋置于坑底中心位置 ,距地表 1m,两坑示踪源层尺寸均为 5.5cm× 0 .6 cm。分别于埋置示踪源层后的第 783d(F坑 )和 10 72 d(C坑 )进行解体采样。使用专门制作的采样定位环 ,分层、分环采样。垂向分层 ,每层厚 1cm;水平方向分环 ,环的直径为 3～ 2 7cm,分 9种尺寸。在 C坑和 F坑分别采土样 2 4 1和 2 13个。用 Na I(Tl)γ谱仪测量土样中85Sr、13 4Cs和60 Co的活度 ,得到两坑中三种核素的比活度分布曲线。结果表明 ,13 4Cs和 60 Co的比活度峰在两试验坑中垂向迁移距离均小于 1cm,但也有一小部分迁移距离较大 ;而 85Sr的比活度峰在人工喷淋条件 (喷淋强度 1.5cm/d)的 F坑 ,向下迁移了约 13cm,在天然条件的 C坑 ,比活度峰仍在示踪源层 ,但在上、下二个方向上明显展宽。另外 ,还发现在水平方向上径向距为 11.3cm(F坑 )和 12 .8cm(C坑 )

To study two dimension migration at vertical and horizontal direction of radionuclides in loess aerated zone, the soil samples in test pit C (under natural condition) and test pit F (under artificial sprinkling condition) were taken and measured. Mixture layer of 85 Sr, 134 Cs, 60 Co with soil which dimension was φ5.5 cm×0.6 cm was buried at the centre of test pit bottom 1 m underground. The soil samples in test pits F and C were taken respectively at 783 and 1 072 days after the tracers were buried in the test pits using a set of specially made iron circles and by means of dividing layers at vertical and cutting rings in horizontal direction. Each layer is 1 cm thickness and 9 diameters of iron circles are 3～27 cm. The total number of samples in test pit C and test pit F are 241 and 213, respectively. The radioactivity of 85 Sr, 134 Cs, 60 Co in samples are measured by γ spectrometers and then the specific activity distribution of 85 Sr, 134 Cs, 60 Co in test pits F and C are obtained. The results show that in two test pits the specific activity peak of 134 Cs and 60 Co moved less than 1 cm at vertical but a small part of nuclides migrated quickly; the specific activity peak of 85 Sr in test pit F moved about 13 cm downward and in test pit C is almost still on the tracer layer but the both sides of the peak were spread out obviously. There are 85 Sr, 134 Cs and 60 Co in the samples which were taken in horizontal direction with radial distance of 11.3 cm (test pit F) and 12.8 cm (test pit C). (