[Clas12tdg] shielding study

[David Kashy]

Hi All,
I put a set of pictures from Alex Vlassov in the following folder
M:\hallb_eng\CLAS12\Beamline\Vlassov shielding pictures 9_09

After the review, we will need to take a close look at this and see how 
it can be implemented. If there are problems we may need to ask Alex to 
run different geometry.

Here is the note from Alex that defines the materials.

> Hi Dave,
> I am sending you pictures of the design I use.
> yellow = tungsten
> blue = aluminum
> black ( grey ) = stainless steel
> Let me know if you have questions, I'll come and explain.
> - Alex


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Dave