Proton dose peak in material interface

Hello to all,

I am attempting to simulate the dose deposition of a 150 MeV in an optic fiber composed of PMMA and polystyrene set in a PMMA phantom but a peak with a maximum greater than expected was observed.

Afterwards I used a simpler simulation with a polystyrene block between two of PMMA to see if the cause was the binning chosen but have been unable to identify the origin of the peak, which is still observed in the interface between the blocks.
The input is
IntStudyProton.inp (2.3 KB)
A plot with the peaks follows.

I would be grateful if you could help.
Thank you in advance and kind regards,
Daniel Salgueiro

Dear @daniel.salgueiro

Thank you for your question.
From the input file you have attached, between the layers of PMMA and polystyrene there are two thin layers of air (0.001-cm thick). Unfortunately, you have not defined the optical properties of the AIR material, which means that the optical photons are not transported in those thin layers, creating the peaks in your picture. As you can see in the picture below, once you include OPT-PROP for AIR, the dose becomes a smoother function. Alternatively, if the air is not needed in your design, there is no problem if the PMMA/polystyrene layers are simply in contact, without air in between.

I hope this solves the problem.
Best regards,
Mario Sacristan

1 Like