南沙海域沉积物岩心228Ra和228Th的深度变化
Depth profiles of 228Ra and 228Th in sediment cores in Nansha sea area
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摘要: 用HPGe γ谱方法测定了6个来自南沙海域沉积物岩心的228Ra和228Th.测定结果如下：228Ra的放射性比活度变化范围为（15.73±1.00）Bq·kg-1至（44.35±1.69）Bq·kg-1，平均值的变化范围为（17.86±0.98）Bq·kg-1至（39.78±1.76）Bq·kg-1；228Th的放射性比活度变化范围为（13.62±0.67）Bq·kg-1至（49.21±1.05）Bq·kg-1，平均值的变化范围（17.30±0.55）Bq·kg-1至（42.89±0.99）Bq·kg-1.与其他海域比较发现，本研究海域的228Ra和228Th比活度及平均值比其他大部分海域稍低.比较6个岩心的结果发现，228Ra和228Th的变化范围基本相同，同时深度变化趋势也非常一致，表明在该研究海域，228Ra和228Th在不同深度处都基本上达到了放射性平衡，没有明显的过剩228Ra存在.这两个核素的深度变化趋势大致分为两种情况，一是随深度的增加有一个微弱的增加趋势，但在中间深度处有一个突然减小的变化；二是随深度的增加呈现出逐渐减小的趋势，但有两个岩心在最深层段出现较大的变化.Abstract: 228Ra and 228Th in six sediment cores in Nansha sea were measured by HPGe gamma spectrometry. The results showed that the activities of 228Ra in these cores ranged from (15.73±1.00) Bq·kg-1 to (44.35±1.69) Bq·kg-1 and the range of the average value was (17.86±0.98) Bq·kg-1 to (39.78±1.76) Bq·kg-1. As for 228Th, the activity ranged from (13.62±0.67) Bq·kg-1 to (49.21±1.05) Bq·kg-1 and the range of the average value was (17.30±0.55) Bq·kg-1 to (42.89±0.99) Bq·kg-1.Comparing with results in other sea areas, the content and average value of 228Ra and 228Th were slightly lower than those in most of other sea areas. After comparing the activities of the 228Ra and 228Th in the six cores, it was found that their changing ranges were basically the same, and the trends of depth profiles were very consistent, indicating that 228Ra and 228Th from the samples in the study area reached radioactive equilibrium, with no apparent excess 228Ra present. The depth profiles of the two nuclides could be roughly divided into two types, one was a slight increase with the increase of depth, but there was a sudden decrease in the middle depth; while the other was a gradual decrease with the increase of depth, but there were greater changes in the deepest segment in two cores.
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Key words:
- HPGe gamma spectrometry /
- radionuclide /
- sediment core /
- depth profile
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