How to simulate at very low energies

Hello there,
i was wondering if there are any tricks to make simulations at very low energies more efficient and accurate.
Im trying to simulate Xrays in the <500eV Range but that takes insanely long due to the very small efficiency of xray production at that energy. I’ve found ways to bias the bremsstrahlung but am still confused how i would go about biasing bremsstrahlung and pixe together.
Ive tried running a few simulations with the Em_penelope and the Em_standard_opt4 physics lists with limited success, meaning extremely long simulation duration for a lackluster spectrum. Are there any physic lists that support my usecase better?

Thanks for reading!

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