Reyes Erika, Marques Leila S
Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão, 1226, CEP 05508-090 São Paulo, SP, Brazil.
Appl Radiat Isot. 2008 Oct;66(10):1531-42. doi: 10.1016/j.apradiso.2008.04.003. Epub 2008 Apr 6.
Activity concentrations of dissolved (234)U, (238)U, (226)Ra and (228)Ra were determined in ground waters from two deep wells drilled in Morungaba Granitoids (Southern Brazil). Sampling was done monthly for little longer than 1 year. Significant disequilibrium between (238)U, (234)U and (226)Ra were observed in all samples. The variation of (238)U and (234)U activity concentrations and (234)U/(238)U activity ratios is related to seasonal changes. Although the distance between the two wells is short (about 900 m), systematic differences of activity concentrations of U isotopes, as well as of (234)U/(238)U, (226)Ra/(234)U and (228)Ra/(226)Ra activity ratios were noticed, indicating distinct host rock-water interactions. Slightly acidic ground water percolation through heterogeneous host rock, associated with different recharge processes, may explain uranium and radium isotope behavior.
测定了在巴西南部莫伦加巴花岗岩体中钻的两口深井地下水中溶解的（234）U、（238）U、（226）Ra和（228）Ra的活度浓度。每月采样，持续时间略超过1年。在所有样品中均观察到（238）U、（234）U和（226）Ra之间存在显著的不平衡。（238）U和（234）U活度浓度以及（234）U/（238）U活度比的变化与季节变化有关。尽管两口井之间的距离很短（约900米），但仍注意到U同位素活度浓度以及（234）U/（238）U、（226）Ra/（234）U和（228）Ra/（226）Ra活度比存在系统差异，表明存在不同的主岩 - 水相互作用。与不同补给过程相关的微酸性地下水通过非均质主岩的渗流可能解释了铀和镭同位素的行为。
