  The Casimir energy of a semi-circular cylindrical shell is calculated by
making use of the zeta function technique. This shell is obtained by crossing
an infinite circular cylindrical shell by a plane passing through the symmetry
axes of the cylinder and by considering only a half of this configuration. All
the surfaces, including the cutting plane, are assumed to be perfectly
conducting. The zeta functions for scalar massless fields obeying the Dirichlet
and Neumann boundary conditions on the semi-circular cylinder are constructed
exactly. The sum of these zeta functions gives the zeta function for
electromagnetic field in question. The relevant plane problem is considered
also. In all the cases the final expressions for the corresponding Casimir
energies contain the pole contributions which are the consequence of the edges
or corners in the boundaries. This implies that further renormalization is
needed in order for the finite physical values for vacuum energy to be obtained
for given boundary conditions.
