The inner darkness consists of one region:-
The shape and size of this region depends the detector being modelled. For SNO it is a barrel shape made by rotating around a quadratic to form the side and using two planes for the top and bottom. This shape is an approximation as, in reality, the cavity walls vary in radius at any given height by about 50cm. However, the particular quadratic used in SNOMAN to model this shape has an rms deviation of 14.1cm from the real shape, and a maximum deviation of 82.6cm.
For Mini-SNO the shape is a block.
The user can disable this region so long as the counting room, urylon, shotcrete, and rock regions are also disabled. In this case the panel zones terminate in the outer darkness.