Re: Back-of-the-envelop photon estimates

[Will Brooks <brooksw@jlab.org>]

Hi,

 I meant 'real' as distinct from 'calculated by us', not to disparage the existing experimental measurements. What I was thinking is to use a calibrated photodiode to do a direct measurement of the number of photons per MeV. But maybe it has already been done, I haven't finished wading through all the many writeups.

 Anyway, if you say a factor of 2 less light is quite possible, then that is not very different from the factor of 3.5 between the PDG number and the number in the specifications document, they are beginning to converge.

Thanks,

 - Will

Pine.LNX.4.58.0905191417580.26027@elton01.jlab.org" type="cite">

I think you are right and UofR has many measurements of the attenuation of
light as a function of wavelength. There are been many discussions about
what fraction should actully be used [see ref. from the calorimeter
review Feb 2008]. A factor of two is quite consistent, which brings the
numbers closer to measured numbers.

In any case, I hope that our guys here will soon come up
  

with a more quantitative estimate based on the absorption and emission
spectra. Also, we should try to do a real measurement.
    

What is closer to a "real measurement" than measurements of photoelectrons
obtained from the Bcal prototype [see GlueX-doc-1069 and the cal NIM
article]? This is what the numbers are normalized to.