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Re: more on BCAL light yield estimates
Dear George,
I think there has been a misunderstanding of my point:my point was that
although the green gives much more light to start with (especially the
double clad one) if one goes after about 2m ,the total light-folding in
the QE as well- is much reduced.I do not claim that is the same as the
blue ,I
it is about half (60-75%) of the blue.
So the bottom line was that it not worthwhile bying the expensive green
fibers if we are going to use PM read-out for the outer layers.
Cheers,Christine
> Hi Christina:
>
> As you noticed with Alex's messages, we have been in frequent
> communication on the issue of number of photo-electrons from the BCAL.
> I have a couple of comments on your message and Alex's analysis. My
> comments do not alter any conclusions but offer a bit more refinements
> for incorporation if work we need to pursue further on this matter.
>
>
>>>> "Christina Kourkoumeli" <hkourkou@phys.uoa.gr> 11/15/07 10:26 AM >>>
>>>> Dear all,
>>>> Let me also add some input to these arguments:few years ago I have
> done
>>>> exactly what Alex did:I took the transmission spectra measured in
> Regina
>>>> and available in the portal for different lengths of fibers and for
> blue
>>>> and green fibers digitized them after normalizing to the tails and
>>>> furthermore I have multiplied by a typical Bialkali QE (all as a
> function
>>>> of lambda ). After the product was done then I observed the
> following:
>>>> at 5cm the green gave as much light as the blue
>>>> but at 175cm (the longest length available) the green was only 75%
> of the
>>>> blue. This was also verfied by us with a rough experiment using UV
> light
>>>> and green/blue fibers.So our conclusion was that the green fiber is
> not
>>>> justifiable for a PM read-out.
>
>
> A bialkali PMT has a Q.E. curve shown in Alex's message of yesterday.
> It's fairly flat between ~400-440 nm at around 23%. Even as far as ~
> 500 nm, Q.E. is around 15%. A blue fiber with peak emission at ~ 430
> nm, at a distance from the source of 100 cm the peak emission is at ~
> 470 nm with very little strength left below 450 nm. A green SciFi, on
> the other hand, has no emission whatsoever below 470 nm at 100 cm from
> the source. So, I am surprised that the combination of green SciFi and
> blue PMT will give as much light as the same PMT with blue SciFi, UNLESS
> the latter has indeed lost so much of the "primary" wavelengths due to
> absorption right at the source while the green SciFi has not.
>
> One also has to be careful to compare emission spectra of identical or
> very similar types of SciFi's. For example, Alex used the curves from
> Kuraray for SCSF-78 to base his calculations, however, he normalized to
> the curve shown by Bicron for BCF-12 to extrapolate to the source. For
> "proof of principle", this is fine, however, there are some differences
> that will alter the final numbers. SCSF-78 has a peak wavelength of 450
> nm and high photon yield (Kuraray's claim without numbers attached).
> BCF-12, on the other hand has a peak wavelength of 435 nm. Normalizing
> the latter to the former is good for showing the effect but will not
> give as accurate numbers as one will get with SciFi's of the same kind.
>
>
>>>> Concerning the absolute numbers ,with different MC we always got
>>>> collection efficiency from both sides of the fiber higher than 9% so
> we
>>>> always assumed that it was 9% per side.
>>>> But I do agree that the spectrum after 2m of (175cm) has to be
> normalized
>>>> to the 2cm one-absolute measurement-and then multiplied by the
> functional
>>>> SiPM or PM efficiency to arrive at the right numbers.
> Cheers,Christine
>
> Both GEANT-based and GUIDEIT - based simulations show 9.3% per side as
> well. We will figure out what the "true" number is and document it by
> calculations for all of us to agree upon.
>
> Cheers,
>
> George
>
>
>
> > Dear Colleagues
>>
>> It is important for us to understand the apparent factor of 4
> discrepancy
>> between the photoelectron yield estimates and measurements for
>> cosmic rays using the BCAL test module. I find the same factor of
>> 4 (roughly) as George -- but I get there by a somewhat different path.
>>
>> Please read the attached and comment.
>>
>> Our goal should be to produce a note on our understanding of light
>> yields since setting specifications for the fibers and SiPM's depend
>> on this. In my role as Design Report editor I will generate this
> note
>> with help and input from others. I will also be spending the first
> week
>> of December in Regina working with my good friends there on the BCAL
>> section of the Design Report.
>>
>> Cheers
>> Alex
>> --
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Alex R. Dzierba
>> Chancellor's Professor of Physics (Emeritus)
>> Department of Physics / Indiana U / Bloomington IN 47405 /
> 812-855-9421
>> JLab Visiting Fellow
>> Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 /
>> 757-269-7577
>> Home Phone: 812-825-4063 Cell: 812-327-1881 Fax: 866-541-1263
>> http://dustbunny.physics.indiana.edu/~dzierba/
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
>