Hello, Mike et al., 

you can correct for self-absorption using the "self-absorption correction tool" in Athena, as long as the chemical composition of your sample is known.

In case it's not possible to determine the chemical composition of you sample, and your sample is conductive, then running your experiment in total electron yield (TEY) mode would be an alternative.

If you're sample isn't suitable for TEY, and the only choice you have left is to run it in fluorescence mode, then you should dilute your sample to a total concentration of P of ~ 0.1 - 0.15% to avoid self-absorption.

It's very important to think through your experiment/samples before you get to the beamline as it avoids you running into such issues, saving you a lot of time. 

Hope it helps ;)

 - Dalton Abdala