Analytical calculations of the radiation length for the Barrel Calorimeter of the GlueX Project are presented. These show that the full thickness radiation length ranges from 18-20 X_0 depending on the thickness of the aluminum backing plate and the analytical formalism used.
ZP checked all numbers in the previous documents and corrected errors in the calculation of Xo using all formulae. The numbers for eqs. 5 and 6 (as calculated by hand and via Mac Grapher equation macros) are in excellent agreement with the PDG values for the elements an mixtures in question and additional ones determined as cross checks.
