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Dear Will,<br>
<br>
30 RL of tungsten is 10.5 cm. If we put the step there, then the first
10.5 cm will have ID 4.0 cm and the next 4.5 cm with a lightly larger
ID. <br>
<br>
I suspect that a proper clean-up collimator should be separated from
the first collimator so particles emerging at large angles have
distance to diverge before being stopped by the second collimator.<br>
<br>
Please email back your thoughts so I can give Dave an answer tomorrow.<br>
<br>
- Larry<br>
<br>
Will Brooks wrote:
<blockquote type="cite" cite="mid:4CB81949.1080506@jlab.org">
Dear all, <br>
<br>
I will think about it further, but my first inclination is not to have
a step. A collimator needs to either touch the particles or not, and
any reduced thicknesses will just increase the exposure to showers. If
the length of the collimator can be made to be quite a bit longer, then
a step will possibly help, but I think we would like to have a good
solid 20 radiation lengths for anything where we expect showering
particles to hit.<br>
<br>
Cristian simulated the entire collimator as tungsten. However, if our
instincts are correct, only the inner collimator matters. He and I
discussed this yesterday afternoon, and he was planning to launch a job
Thursday night with inner collimator made out of tungsten and outer
collimator made out of Pb. If there are no job crashes, we will have
the results today (Friday). However, I would not advocate waiting for
the results before proceeding. The inner W collimator can only help,
and probably is all that is really needed.<br>
<br>
Thanks, <br>
<br>
- Will<br>
<br>
<br>
On 10/14/10 11:05 PM, Larry Weinstein wrote:
<blockquote type="cite" cite="mid:4CB7707F.3070808@odu.edu"> Dear
Folks,<br>
<br>
The downstream collimator is a cylinder 40 mm ID, 98 mm OD and about 6"
long. It is currently lead and we would like it to be tungsten (based
on Cristian's simulation results).<br>
<br>
1) The downstream collimator will be tungsten ID 40 mm, OD 76.2 mm
with a lead jacket ID 76.2 mm, OD 98 mm. It will take 4-6 weeks to get
a bigger piece of tungsten so that the entire piece is made of
tungsten. We do not have that time.<br>
2) Dave K suggests that we taper or step the ID of the tungsten to
reduce the effects of a possible misalignment and to let the tungsten
also be its own clean-up collimator. Do we want the collimator to be
ID 40 mm for the first half (3") and then ID 42 mm for the 2nd half? <br>
a) Do we want a step in the collimator?<br>
b) If so, where do we want the step (how far downstream)?<br>
c) How big do we want the ID change to be?<br>
<br>
I will discuss this with Dave Monday (and I will not be available
tomorrow).<br>
<br>
- Larry<br>
<br>
-------- Original Message --------
<table cellspacing="0" cellpadding="0" border="0" class="moz-email-headers-table">
<tbody>
<tr>
<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Subject: </th>
<td>collimator at target</td>
</tr>
<tr>
<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Date: </th>
<td>Thu, 14 Oct 2010 16:56:55 -0400</td>
</tr>
<tr>
<th valign="BASELINE" nowrap="nowrap" align="RIGHT">From: </th>
<td>David Kashy <a href="mailto:kashy@jlab.org"><kashy@jlab.org></a></td>
</tr>
<tr>
<th valign="BASELINE" nowrap="nowrap" align="RIGHT">To: </th>
<td>Larry Weinstein <a href="mailto:weinstei@jlab.org"><weinstei@jlab.org></a></td>
</tr>
</tbody>
</table>
<br>
<br>
<pre>Hi Larry,
The shop tells me to get tungsten of 4" OD will be 4-5 weeks just for
the material, I called a place my self and they said 5-6 weeks. I don't
think we should risk the delay since there is a piece at the shop that
is 3" od and just over 6" long.
I did have an idea that you might want to consider.
We could make a taper or step in the ID so that slight miss alignment of
the collimator has less effect that would be something like making the
first 2, 3 or 4" with 40 mm id and the final 4 , 3 or 2 inches is 42mm
or 44mm
Let me know
Dave
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<pre cols="72" class="moz-signature">--
Sincerely,
Larry
-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 5809 (fax)
<a href="mailto:weinstein@odu.edu">weinstein@odu.edu</a>
<a href="http://www.physics.odu.edu/~weinstei">http://www.physics.odu.edu/~weinstei</a>
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