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Dear Dave,<br>
<br>
Thank you very much. We will probably want to build this wall during
the next major down time, possibly Tuesday.<br>
<br>
- Larry<br>
<br>
David Kashy wrote:
<blockquote cite="mid:4D41F459.7020302@jlab.org" type="cite">
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Hello Larry,<br>
I have verified that we can stack a concrete wall up to 5 ft high and
10 ft long on the decking next to the pair spectrometer magnet if
necessary. I used a block density of 150 lb/cubic ft. I think this is
what we have. <br>
<br>
<br>
Thanks<br>
Dave<br>
<br>
<br>
<br>
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On 1/26/2011 4:55 PM, Larry Weinstein wrote:
<blockquote type="cite" cite="mid:4D409843.3060700@odu.edu">
Dear Folks,<br>
<br>
Recommendation: In order to be very conservative, build a concrete wall
on the beam left side of the collimator box, frascati magnet 1, and PS
magnet. The wall would be about 10' x 5' x 1' and require 200 blocks.
It should be built during the next extended down time (Tuesday?) so as
not to interfere with taking data.<br>
<br>
Details: I spoke to Pavel Degtiarenko, the radiation and shielding
expert. He says that there is very little useful data about the effect
of radiation on electronics because the response of electronics to
radiation is highly variable. He also noted that the existing BPM
amplifiers have probably already suffered some radiation damage and
that this damage is cumulative. He also said that most of the
radiation is probably high energy particles that can be shielded by a
shield wall (if we know the approximate source location.)<br>
<br>
This means that we probably want to add shielding to reduce the
probability of catastrophic BPM failure.<br>
<br>
RadCon gave us the badge readings today (thanks, Becky!). <br>
<br>
<table border="0" cellpadding="0" cellspacing="0"
width="450">
<col span="6" width="75"> <tbody>
<tr height="13">
<td align="right" height="13" width="75">66016</td>
<td align="right" width="75">331</td>
<td colspan="3" width="225">1' from top of Acc IOC
rack</td>
<td width="75"><br>
</td>
</tr>
<tr height="13">
<td align="right" height="13">66017</td>
<td align="right">197</td>
<td colspan="4">2.5' from top of Acc IOC rack, in
front of concrete wall</td>
</tr>
<tr height="13">
<td align="right" height="13">66018</td>
<td align="right">220</td>
<td colspan="4">2.5' from bottom of Acc IOC rack, in
front of concrete wall</td>
</tr>
<tr height="13">
<td align="right" height="13">66019</td>
<td align="right">66</td>
<td colspan="4">2.5 from top of Acc IOC rack, behind
concrete wall</td>
</tr>
<tr height="13">
<td align="right" height="13">66020</td>
<td align="right">73</td>
<td colspan="4">2' from bottom of Acc IOC rack,
behind concrete wall</td>
</tr>
<tr height="13">
<td align="right" height="13">66023</td>
<td align="right">92</td>
<td>on ioc ptarg</td>
<td><br>
</td>
<td><br>
</td>
<td><br>
</td>
</tr>
<tr height="13">
<td align="right" height="13">66024</td>
<td align="right">254</td>
<td colspan="3">in front of new lead wall, 5' from
floor</td>
<td><br>
</td>
</tr>
<tr height="13">
<td align="right" height="13">66025</td>
<td align="right">191</td>
<td colspan="3">L1-15 on left (upstream) side of IOC</td>
<td><br>
</td>
</tr>
<tr height="13">
<td align="right" height="13">66026</td>
<td align="right">632</td>
<td colspan="2">on railing opposite PS</td>
<td><br>
</td>
<td><br>
</td>
</tr>
<tr height="13">
<td align="right" height="13">66027</td>
<td align="right">230</td>
<td colspan="4">upstream, beam side of lead wall on
ioctorus</td>
</tr>
<tr height="13">
<td align="right" height="13">66028</td>
<td align="right">126</td>
<td colspan="4">downstream, outside of lead wall on
ioc torus<br>
</td>
</tr>
</tbody>
</table>
The first column is the badge number, the second is the radiation dose,
and the third is the location.<br>
<br>
A few notes: Badge 66026 with a reading of 632 mr is located where the
radcon photon probe was located before 1/20, on the railing of the
space frame close to the pair spectrometer. The probe was reading
about 50 mr/hr at that location.<br>
<br>
Badge 66019, behind the concrete wall, is located directly on top of
the accelerator BPM amplifiers and right next to the radcon photon
probe which is currently reading 5 mr/hr. This is consistent with
badge 66026.<br>
<br>
badges 66016, 7, and 8 are located on the accelerator BPM amplifier
rack. The highest one (66016) has the highest dose and has much less
of the lead shielding on the lead wall between it and the beam line.
The concrete wall (either 6" or 12") reduces the rate from about 200 mr
to 70 mr (comparing badges 17 and 18 with 19 and 20). (Note that the
badges were placed before the BPE shielding was added.)<br>
<br>
The maximum thickness of the lead wall reduces the dose from 254 (badge
66024) to 92 (badge 66023).<br>
<br>
The radiation level is not much less a little further down-beam on rack
L1-15 (191 mr at badge 25).<br>
<br>
The dose decreases about a factor of two between the upstream beam side
of the lead wall on ioctorus to the downstream outside of the lead wall.<br>
<br>
Summary: The dose at iocptarg, ioctorus and the accelerator BPM
amplifiers are within a factor of two. The shielding reduces the dose
significantly.<br>
<br>
There is floor space or floor weight capacity to place any more
shielding near the racks. THis means that the only place to add
shielding is near the source. Since the source probably includes the
collimator box, convertor and chicane, we should build a concrete wall
on the beam left side from the PS magnet going as far upstream as
possible.<br>
<br>
<pre class="moz-signature" cols="72">--
Sincerely,
Larry
-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 3038 (fax)
<a moz-do-not-send="true" href="mailto:weinstein@odu.edu">weinstein@odu.edu</a>
<a moz-do-not-send="true" href="http://www.lions.odu.edu/%7Elweinste/">http://www.lions.odu.edu/~lweinste/</a></pre>
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