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Question question about the reflectivity index inside Look up tables 

Forum: Processes Involving Optical Photons
Date: 30 Sep, 2015
From: sauvestre <sauvestre>

Hello, I am simulating a Li glass scintillator used for neutron detection.

The glass is a cylinder of 1,86 cm diameter and 0,95 cm thickness.

The distribution of the emission spectra (due to Ce3+ activators within

the glass) is in the UV-visible range with a maximum wavelength around 395 nm.

I use for sure the processes involved in the optical photon package. My geant4

version is geant4.10,0. The faces of the glass are covered by a TiO2 paint

except at the rear side coupled to a PM via an optical grease. I have used the

LUT given in RealSurface1.0. In my code i have set:


opAirSurface->SetFinish(polishedtioair); but also ground or etched to test their effect


If i look at the reflectance index given by DupontTM or in NIM A 704(2013)

104-110 (Bicron Manufacturer)i have the figures attached.

On the basis of these figures, i though that part of the optical photons

generated by ionisation of light charged particles in the glass will be lost

(10% around 400 nm) while transmitted through the paint. Instead of that, all

the optical photons are reflected in my code and only absorption is seen

despite the small size of the glass (this trend is normal however,i.e.

absorption length are tabulated in my code thanks to Bollinger article NIM 17


I try to understand the format of tables given in RealSurface1.0. There are

many 0 but sometimes values appear that i can't understand at all even after

reading the article of Martin Janecek and William W. Moses (IEEE TNS vol 57 n3

 (2010) 964-970).

My questions are:

do i use correctly the LUT and if not where am i wrong? Do i have to add

something else that i have missed (see the previous three lines of the code).

Is there any method to extract a figure giving reflectance index versus

wavelength from the data files in RealSurface1.0?

If i change the type of the surface (etched, ground) i see no differences at

all? Is it explained by the small size and thus the low number of reflexion

before entering the photocathode?

Hope i have been clear enough. Thanks in advance for any answer. Jean Etienne Sauvestre


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