How to figure out the wave type for scattering boundary condition?

Hello,

I'm a newbie in Comsol and I have a question, which you might be able to answere.

I want to simulate the absorption and scattering of nanoparticles illuminated with an incident plane wave. My nanoparticle is a disc and the environment is spherical. Now I want to apply a scattering boundary condition but how do I know which wave type I have to choose? I would suppose it's spherical but how do I know that?

Best regards...