Re: light collection in bcal outer layers

["George Lolos" <George.Lolos@uregina.ca>]

Hi Elton:

Thanks for the note.  It pretty much agrees with the Blake studies for the Module 1 beam tests.  One should indeed do better than 75% in mirror reflectivity but 95% across the scintillation spectrum is not as easy as it looks.  We had CERN aluminise mirrors for the Hall-A aerogel cerenkov and the reflectivity curves we obtained as a function of wavelength would average out around 87-90% and CERN knew how to do mirrors!  Considering that the 45 degree parts will be machined not cast, their surface smoothness cannot be as good as cast so if we get an effective mirror reflectivity of 85% will be good.  Nevertheless, one thing that one sees clearly is the penalty we pay for long light guides compared to short ones.

The idea of using 3" PMT's to increase efficiency is worth pursuing, however, the residual magnetic field effects also increase with increasing photocathode area.

Cheers,

George

>>> Elton Smith <elton@jlab.org> 01/19/08 11:34 AM >>>

Dear collaborators,

I have posted a preliminary study of the light collection though light
guides for the outer layers of the bcal in GlueX-doc-959.

Cheers, Elton.




Elton Smith
Jefferson Lab MS 12H5
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elton@jlab.org
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