Re: question on pair spectrometer shielding

[Alexander Somov <somov@jlab.org>]

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
>