# BCAL Pb Sheet Widths

From GlueXWiki

Here are the long awaited specifications for the Pb widths and numbers. The basis for the numbers are the following:

- The assumption was that the active matrix will be 23.5 cm or 190 layers assuming 1.24 mm vertical pitch. I am giving you these numbers so one can correct accordingly for the final thickness and perhaps different pitch but the differences will be very minor and will affect only the number of sheets for the last step in the pyramid.
- I have added +1.0 cm to the minimal width required by an ideal geometry and rounded to the nearest integer. For example, the bottom of the first step should be (after machining) 11.78 cm. I then require all the layers (21) in that first step to be 13.0 cm to allow us for possible variations during construction. In other words, I added 0.5 cm of "slop" on either side with respect to the center line that all dimensions are referred to.
- This way I tried to minimize the widths without sacrificing much in lead and SciFi wastage. One can increase the number of widths by using 0.5 cm increments but I am not so sure that we stand to gain more than we lose if the supplier balks at the number of different widths. It also makes Pb sheet sorting a bit easier.

So we need (per module):

- 21 sheets of 13.0 cm width (step 1)
- 42 sheets of 12.0 cm width (steps 2 and 3)
- 21 sheets of 11.5 cm width (step 4 or can be combined with 2 and 3 as 12.0 cm)
- 63 sheets of 11.0 cm width (steps 5, 6 and 7)
- 42 sheets of 10.0 cm width (steps 8 and 9)