thickness estimates for wire frames

[Simon Taylor <staylor@jlab.org>]

Hi.

I estimate the following thicknesses in radiation lengths for normally 
incident particles (to show the scale)
for the wire frame material ideas we discussed on Thursday: 

Material                        X/X0
------------------------------------------
Solid G10/FR4              3.13%
2 FR4 skins+HF31        1.05%          Low density foam
2 FR4 skins+IG110       1.11%          High density foam

These numbers are for each wire  frame (so 5 mm thickness).
I find that the thickness of the composite is completely dominated by 
the FR-4 skins (I assumed a density of 1.9 g/cm^3 for FR-4 but have seen 
numbers as low as 1.7 g/cm^3) and that the difference in this metric 
between the high and low density foam is negligible.

Simon