Dear all,
Thanks for your answer,Scott Calvin!
I guess the value of sigma2 is normal, which is 0.0075.
But your suggestion about the existing of modest degree of oxidation or other impurities is possible, I will think over it ^^
Actually this morning I improved this situation and got a reasonable CN value by trying self absorption correction to my data in Athena ( because I used fluorescence measurement). I think it is because the amplitude of my data increased after self absorption correction, so the CN of 1st shell also increased from around 8 to around12, which is more reasonable. So I really want to know if this self absorption correction really makes sense, or it might be just an accident??
Thanks a lot~