<html>
<head>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix">Eugene,<br>
<br>
One needs to measure the ratio of the pair spectrometer rate to
the TAC counter <b>for a particular set of beam photon
populations.</b> The populations are defined by those beam
photons that are in coincidence with each of the tagger detector
channels. None of this is meaningful without the tagger in
coincidence. As soon as you change the radiator, the population
being selected by the tagger coincidences changes.<br>
<br>
-Richard Jones<br>
<br>
<br>
<br>
<br>
On 7/10/2012 10:52 AM, Eugene Chudakov wrote:<br>
</div>
<blockquote cite="mid:Pine.LNX.4.64.1207101016340.21664@jlabl1.jlab.org" type="cite">
<pre wrap="">Hi,
The yesterday's discussion on the photon flux calibration did not
convince me that one desperately needs a 1nA current.
One needs to measure the ratio of the pair spectrometer rate to the
total absorption counter rate (for a given energy bin in the tagger).
This ratio should not be very sensitive to the type of the
radiator. Both detectors see the same photon beam. So, instead of
using a 1nA beam current run one may use a thin radiator or a scanning
wire with a 50nA run. I suppose it is easy to simulate the acceptance
of the pair spectrometer to find out what would be the dependence on
reasonable shifts in the beam spot profile (say, a 20% variation of
the radiator thickness across the beam). One should also keep in mind
that a low current beam might have a different profile with respect to
the full current beam, so this kind of uncertainty always exists.
Eugene
On Mon, 9 Jul 2012, Richard Jones wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hello,
Please remember our biweekly working group meeting this morning at 11:30EST.
The draft agenda is posted in the usual place. Please install links in the
agenda page to any materials that you will be presenting.
-Richard J.
</pre>
</blockquote>
<pre wrap="">_______________________________________________
Halld-tagger mailing list
<a href="mailto:Halld-tagger@jlab.org">Halld-tagger@jlab.org</a>
<a href="https://mailman.jlab.org/mailman/listinfo/halld-tagger">https://mailman.jlab.org/mailman/listinfo/halld-tagger</a>
</pre>
</blockquote>
<br>
<br>
</body>
</html>