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Re: more on BCAL light yield estimates



Hi,

here's the Saint-Gobain Crystals link for the Bicron fibres info as well 
for anyone interested:
http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC%20Scintillating%20Optical%20Fibers%20Brochure%20605.pdf


-Blake


Alex Dzierba wrote:
> OK - thanks - I was doing a trivial solid angle and there's obviously
> more than that - thanks for the reference as well.
>
> Cheers
> Alex
>
> At 10:51 AM -0600 11/16/07, Blake Leverington wrote:
>> sorry it's (1-cos^2[theta])/2, which includes skew rays as well as 
>> meridional rays to give a trapping efficiency of ~10.6%., so this 
>> 9.3% which cam from Yianna's simulation is lower than predicted.
>>
>> -Blake
>>
>> Blake Leverington wrote:
>>> hi Alex,
>>>
>>> The trapping efficiency for a fiber is (1-cos[theta]^2)/2,  not 
>>> (1-cos[theta])/2 which gives a trapping efficiency closer to 10.6%. 
>>> See http://arxiv.org/pdf/nucl-ex/0404008 on page 8.
>>>
>>> -Blake
>>>
>>>
>>>
>>>
>>>
>>>
>>> Alex Dzierba wrote:
>>>> Thanks to George and Christine
>>>>
>>>> I appreciate and understand the comments - my goal was to
>>>> use other sources to look at the issue and I agree that we
>>>> need to quickly converge on putting down on paper what we
>>>> know and make sure we can agree.
>>>>
>>>> Regarding the capture fraction - I may be making a trivial error
>>>> but it seems that to first order the fraction of the light
>>>> generated at the source, assuming isotropic distribution,
>>>> coming out one end within critical angle theta (measured
>>>> along the fiber) is (1-cos[theta])/2 or the solid angle
>>>> subtended divided by 4pi.  For theta = 27.6 degrees
>>>> this leads to 5.3% out one end.
>>>>
>>>> Cheers
>>>> Alex
>>>>
>>>> At 4:27 PM -0600 11/15/07, George Lolos wrote:
>>>>> 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/
>>>>>>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>