Absorption and diffusion coefficient

Dear @vojtech.stransky ,
I want to ask a question about absorption and diffusion coefficient again(it seems I have asked it ever, but I am not understand it clearly ). How much influence these two parameters have on the calculation of energy deposition, secondary particle and photon count, and material thickness, because some special materials cannot find the corresponding reference data. If there is no impact, I intend to take a value at will.

Dear Xiong,

The absorption and diffusion parameters defined in the OPT-PROP card do not have any influence on the energy deposition and the production of secondary particles. The number of optical photons produced in your material is driven by the OPT-PROD cards associated to this material. For example, the fraction parameter (WHAT(2)) when setting SDUM=SCINTILL corresponds to the photon yield in units of GeV/GeV.

The absorption and diffusion defined for an optical material will, however, influence the transport of optical photons inside the material and incidentally the photon yield of a detector optically attached to the material.

The proper values for the absorption and diffusion are not, in general, intrinsic characteristics of the material as they typically depend on manufacturing process. And unfortunately those properties are seldom specified by the manufacturer. If you could not find values for those parameters, and if it’s not possible to measure them yourself, I suggest you use the values that “best-fit” your expectations.

I attached simulations results for a simple BGO cylinder wrapped in Teflon. Clearly, the fluence of optical photons exiting the BGO volume is influenced by the absorption and diffusion parameters. However, for that simulation, I used absorption and diffusion lengths that are rather short (10cm). Note that the FLUKA default length is infinity in both cases.

opt-prop.flair (10.6 KB)
opt-prop.pdf (13.5 KB)opt-prop

Dear @blefebvre ,
I have understand it and thank you for your reply.