<html>
<head>
</head>
<body text="#000000" bgcolor="#ffffff">
Dear Dave,<br>
<br>
The wall is 10' wide. That is the approximate distance from the short
ladder at the pair spectrometer to the upstream end of that platform.
The wall height would then be beam height plus one foot. (I did not
measure the height so I am not sure whether it would be 4' or 5'.)<br>
<br>
I completely agree that we should not rush into this. I think that the
radiation experience since Thursday indicates that we do not need to do
this immediately.<br>
<br>
- Larry<br>
<br>
David Kashy wrote:
<blockquote type="cite" cite="mid:4D409DCB.8020902@jlab.org">
Hi Larry,<br>
Is this wall 10' high or wide?<br>
If it is 10 ft wide then I guess we need to start it above the floor
level and need to design a beam structure to support it.<br>
<br>
If it is 10 ft tall we will still need to design a structure to keep it
from toppling. <br>
<br>
This wall will weight about 8000 lbs (similar to HYCAL) not a trivial
load and thus we must do it correctly.<br>
<br>
Thanks<br>
Dave<br>
<br>
<br>
<br>
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 width="450" cellspacing="0" cellpadding="0" border="0">
<col width="75" span="6"> <tbody>
<tr height="13">
<td width="75" height="13" align="right">66016</td>
<td width="75" align="right">331</td>
<td width="225" colspan="3">1' from top of Acc IOC rack</td>
<td width="75"><br>
</td>
</tr>
<tr height="13">
<td height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">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 height="13" align="right">66027</td>
<td align="right">230</td>
<td colspan="4">upstream, beam side of lead wall on ioctorus</td>
</tr>
<tr height="13">
<td height="13" align="right">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 cols="72" class="moz-signature">--
Sincerely,
Larry
-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 3038 (fax)
<a href="mailto:weinstein@odu.edu">weinstein@odu.edu</a>
<a href="http://www.lions.odu.edu/%7Elweinste/">http://www.lions.odu.edu/~lweinste/</a></pre>
</blockquote>
<br>
<div>
<hr><br>
<a href="https://www.spamtrap.odu.edu/b.php?i=438400204&m=903a77671a30&t=20110126&c=s">Spam</a><br>
<a href="https://www.spamtrap.odu.edu/b.php?i=438400204&m=903a77671a30&t=20110126&c=n">Not
spam</a><br>
<a href="https://www.spamtrap.odu.edu/b.php?i=438400204&m=903a77671a30&t=20110126&c=f">Forget
previous vote</a><br>
</div>
</blockquote>
<br>
<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 3038 (fax)
<a href="mailto:weinstein@odu.edu">weinstein@odu.edu</a>
<a href="http://www.lions.odu.edu/~lweinste/">http://www.lions.odu.edu/~lweinste/</a></pre>
</body>
</html>