Re: Fiber test stand at JLAB (fwd from lolos)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Wed, 27 Aug 2008 13:29:34 -0600
From: George Lolos <gjlolos@uregina.ca>
To: Beni Zihlmann <zihlmann@jlab.org>
Cc: Hall-D Calorimetry <halld-cal@jlab.org>
Subject: Re: Fiber test stand at JLAB

Hi Beni:

Kathryn has completed the measurements of the number of
photoelectrons for the three Kuraray fibers and two Bicron and we're
now double checking to make sure the numbers stand the test of
different methodology.  As they stand now, they're in agreement with
the numbers in your report and Kathryn will post them when we're done.

I have some questions on your report for clarifications:

When I look at figure 2 (the LED ADC spectrum) the mu value gives you
~2.5 photoelectrons.  However, with a mean of ~2.5 pe's I would
expect the height of the second peak to be a bit higher than that of
the 1st. and it's not.

The gain of the XP2020 at -2200V that comes out at 2 x 10^6 is low
for the 12-stage PMT.  I looked back at measurements we had done a
number of years ago with a number of XP2020's and we were getting
more like 10^7 at 2000 V with voltage divider Type A.   Did you use
such a highly "progressive" dynode chain to increase the peak pulse
current?  I would have thought that for low light measurements a Type
A dynode chain will give you excellent gain at low bias and you
wouldn't need an external amplifier that can never do much good to
peak width.

In any case, as I stated above, Kathryn gets consistent numbers but I
am looking to attach some measure of "error" in the extraction to
increase confidence because dealing with small numbers of
photoelectrons to begin with, agreement can come down to decimal
numbers.

Cheers,

George

On 26-Aug-08, at 7:42 AM, Beni Zihlmann wrote:

> Dear Colleagues,
> I put description of the fiber test stand here at JLAB on the wiki
> together with
> some first results. Have a look at:
> http://www.jlab.org/Hall-D/software/wiki/index.php/
> Fiber_Test_Stand_at_JLAB
>
> cheers,
> Beni
>