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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 cite="mid:4CB7707F.3070808@odu.edu" type="cite">
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 class="moz-email-headers-table" border="0" cellpadding="0"
cellspacing="0">
<tbody>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Subject:
</th>
<td>collimator at target</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Date: </th>
<td>Thu, 14 Oct 2010 16:56:55 -0400</td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">From: </th>
<td>David Kashy <a moz-do-not-send="true"
href="mailto:kashy@jlab.org"><kashy@jlab.org></a></td>
</tr>
<tr>
<th align="RIGHT" nowrap="nowrap" valign="BASELINE">To: </th>
<td>Larry Weinstein <a moz-do-not-send="true"
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
</pre>
<pre wrap="">
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