Re: Fiber light output specification for KLOE (fwd)

[Elton Smith <elton@jlab.org>]

Dear collaborators,

I sent an inquiry to Stefano Miscetti to find out how KLOE specified the
absolute light yield. Below is his reply:

---------- Forwarded message ----------
Date: Tue, 22 Apr 2008 15:09:27 +0200 (METDST)
From: miscetti <Stefano.Miscetti@lnf.infn.it>
To: Elton Smith <elton@jlab.org>
Subject: Re: Fiber light output specification

Dear Elton,
I agree with you that these measurements are tricky.

Specifically the measurement with beta sources on single
fibers are very complicated for the calculation of Npe/MIP
since to define the MIP crossing the fiber is not straightforward.

There are pubblications on NIM recalling/explaining this kind of
measurements.

We have done something similar in the past and repeating on these
days for our own experiments. However, for the reasons mentioned
above absolute light yield measurements "with single fiber" is
very difficult.

To get a final decision for the fibers and then monitor the
fiber production we have done  (for KLOE) two different things:

i) select the best fibers with test beam/CR test by building
    either boundles of fibers of the same kind, or small
    calorimeter sectors ( see NIMA 370, pag 367-371, 1996)

ii) monitor the arrival of fibers by x-measurement with
    beta sources in current, i.e. we got from the same
    samples of (i) a relative measurement of anodic current
    when illuminating a long fiber with a beta source
    moving over a rail in different position along the
    fiber length. This gave us both attenuation length
    and average current. We repeated the measurement many
    times for  the first tested fibers in order to assign
    a reproducibility  error to the method. We then accepted
    fibers by sampling few of them/each package sent by
    Kuraray only if the average current-attenuation length
    were inside our specified acceptance range.

For the measurement of the absolute light yield and related
problems you can give a look to this great old NIM paper
NIM A 292, 329-336, 1990.


Let me know if this can be useful to you.

If you need more details I have to go back to thesys or
technical notes.

 			Regards,

 				Stefano


On Tue, 22 Apr 2008, Elton Smith wrote:

>
> Dear Stefano,
>
> I am working on the barrel calorimeter for Hall D and you participated in
> our review in February, where you gave us useful suggestions and advice.
>
> We are in the process of finalizing the specification for the fibers of
> the calorimeter and are still trying to decide how to specify the absolute
> light output. Neither Kuraray or St. Gobain (Bicron) specify the absolute
> light yield of the fibers in their specification sheets. (In contrast,
> bulk scintillator is specified in terms of the % of anthracene).
> Experience has shown that the light output gives us the expected
> resolution, but we want to specify and check fibers before gluing them
> into the modules. One possibility is to require a certain number of
> photoelectrons detected from a radioactive source, but these measurements
> are tricky and both the manufacturer and us will need to agree on the
> outcome.
>
> Do you remember how you specified the absolute light yield for your
> fibers? If you still have the actual specification used to purchase
> the fibers and the specific acceptance tests you performed, that would be
> very useful as background.
>
> Thanks so much, Elton.
>
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave
> Suite # 16
> Newport News, VA 23606
> elton@jlab.org
> (757) 269-7625
> (757) 269-6331 fax
>