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Re: question on pair spectrometer shielding



Alex,

Can we have a discussion of this at the working group meeting this 
week?  This iron will make mapping in the pair spectrometer more 
complicated because the iron has to be present during the mapping and 
not allowed to move.  There will be large horizontal forces in addition 
to the weight.  I don't remember discussing this before.  I wonder what 
can be the shielding benefit from this iron outside the region of the 
gap, since it is already shadowed by 2m of yoke iron.

-Richard Jones


Alexander Somov wrote:
> Richard,
>
> There were two main reasons of using the wall after the pair
> spectrometer:
>
>   - to reduce the size of a shielding lead wall after the pair
>     spectrometer; lead bricks are more expensive (if purchase them)
>     than this iron blocks. This blocks should even be available in
>     Jlab. These blocks are also not that heavy (about 1 ton each,
>     8 tons in total) so that they could be placed on the GlueX
>     platform without aditional reinforcing it.
>
> - the wall also reduced remaining bg from the cave. Sweeping magnets
>    deflect particles in horizontal directions.
>
> All in all, after some discussions we decided to use this blocks
> given that they don't  (marginally) affect the cost. They also
> don't hinder moving out detector components.
>
> Cheers,
>         Alex
>
>
>
>
> On Mon, 23 Mar 2009, Richard Jones wrote:
>
>> Alex,
>>
>> I am going through the new geometry for the photon beamline, and have 
>> a question.  What is the purpose of the large iron wall 17.8cm thick 
>> at the downstream end of the pair spectrometer?  It seems that this 
>> will play no role, since there is already much more iron that this in 
>> the yoke and poles of the dipole itself.  Is this a crude description 
>> of the support structure for the magnet?  If it is not needed to 
>> shield the counters then can I get rid of it?  If you think we need 
>> to shield the counters, can we somehow reduce its dimensions? 
>> -Richard Jones
>>
>