highly significantp < 0.001
The correlation between 226 Ra and 232 Th was not significant ( r = 0.47, p > 0.05), whereas a highly significant correlation was observed between 226 Ra and 40 K ( r = 0.77, p < 0.001) and between 232 Th and 40 K ( r = 0.75, p < 0.001).