How to get the scattering cross section of a nano particle using HFSS?

I am trying to use HFSS to get the scattering cross section of a 25nm radium gold ball at the incident wavelength from 200nm to 1000nm.
I do not know how to do it. I can get the RCS of it. But I do not know how to get the scattering cross section.
And I am not sure about the difference between the scattering cross section and the RCS of a nano gold ball.
Could anyone help me on this?
Thanks a lot.