Use of logical border surfaces with reflectivity and transmittance

[dsawkey]

@Frank_Malatino

using a G4LogicalBorderSurface, is it necessary to define a surface going both ways?

G4LogicalBorderSurfaces are defined separately for each direction of propagation. So yes, if your model requires a G4LogicalBorderSurface to accurately model reflector->scintillator transport, you will need to define it.

“A border surface is defined by specifying the ordered pair of physical volumes touching at the surface. Because the pair of physical volumes is ordered, the user may specify different optical properties for photons arriving from the reverse side of the same interface.” (Book for Application Developers)

@Frank_Malatino

When defining the properties REFLECTIVITY and TRANSMITTANCE, does one need to define both, or is one sufficient, given that T = 100% - R (R = 100% - T)?

This is incorrect. REFLECTIVITY is 1-(absorption coefficient). If you want a fraction f1 of photons absorbed, specify REFLECTIVITY = 1-f1. If you want a fraction f2 of photons transmitted, specify TRANSMITTANCE = f2. The rest undergo dielectric-dielectric interaction.

@Frank_Malatino

if one were to use a dielectric as a reflector, example: a sheet of white paper, should the surface be defined as a dielectric_dielectric or a dielectric_metal?

You’ll need to figure out what you want to simulate, and puzzle through the figure in the Book for Application Developers. Do you want opticalphotons propagating in the paper? Do you want total internal reflection? If either, dielectric_dielectric.