陕北黄土高原239+240Pu大气湿沉降历史重建

The Atmospheric Wet Deposition History Reconstruction of 239+240Pu at the Loess Plateau of Northern Shaanxi

重建Pu同位素的大气沉降历史是开展Pu示踪应用以及核事故安全评价的重要基础。本研究根据东京年降水量和239＋240Pu年大气沉降数据，并结合经验模型对陕北黄土高原239＋240Pu年湿沉降通量进行初探。结果表明，1957-2005年间研究区239＋240Pu年湿沉降通量在0.000 2-4.116 7 Bq/m^2之间，累计湿沉降通量为14.08 Bq/m^2；通过与周边土壤剖面的Pu总量对比发现陕北黄土高原Pu同位素的干湿沉降比为1左右。在时间变化上，上世纪60年代初全球大规模核试验导致研究区1963年239＋240Pu湿沉降通量出现峰值，1964-2000年Pu湿沉降通量呈明显减小趋势，2001-2005年亚洲粉尘的地表再悬浮过程使得239＋240Pu年湿沉降通量有所增加。

The reconstruction of wet deposition history of plutonium isotopes is the important foundation for their tracer applications and safety assessments after nuclear accidents. On the basis of annual precipitation and 239＋240Pu annual deposition flux data collected in Tokyo, this study investigated 239＋240Pu annual wet deposition flux at the Loess Plateau of Northern Shaanxi via empirical equations. The results showed that 239＋240Pu annual wet deposition flux was in the range of 0.000 2-4.116 7 Bq/m^2 during 1957-2005 in the study area, and the cumulative wet deposition was estimated to be 14.08 Bq/m^2. Compared the cumulative wet deposition at the Loess Plateau of Northern Shaanxi with the inventory in surrounding soil profiles, we deduced that the wet deposition to the dry deposition ratio in the study region is about 1. For temporal variation characteristics, the maximum annual deposition appeared in 1963 since of the large-scale atmospheric nuclear weapons testing in the early 1960s, and the 239＋240Pu annual wet deposition flux presented an obvious decrease trend from 1964 to 2000. However, annual wet deposition flux of Pu isotopes showed an increase trend during 2001-2005 due to the particle suspension of Asian dusts.