In case variation of material properties (such as the density) as a function of depth must be considered, one should prepare different bodies to be positioned one after the other, so to fill them with the proper different materials.
We remind here that all physical setups must be embedded inside an enclosing volume, defined to be a ``black hole'' material, so to stop the tracking of all escaping particles. We can choose a large sphere (SPH) to describe the enclosing volume.
Since muons must be injected just above the water surface and since, by definition, they cannot be injected in a ``black body'' medium, it can be convenient to define a limited vacuum region just above the water volume. It is convenient to do the same just after the depth at which scoring is performed. All this can be easily implemented by cutting the RPP volume by two planes orthogonal to the Z axis (XYP bodies), respectively at Z = Z and Z = Z such that Z - Z = , where is the desidered thickness of water. The extreme Z coordinates of the RPP body, Z Z and Z Z, will be chosen so that Z - Z and Z - Z will respectively define the desired vacuum layers above and below the water volume.
In summary, the geometrical setup will be the one depicted in Fig.1.
The bodies can be numbered in the data cards according to the following lines:
SPH 1 0.0 0.0 0.0+5000000.0 RPP 2-1000000.0+1000000.0-1000000.0+1000000.0 -100.0+1000000.0 XYP 3 0.0 XYP 4 200000.0 END
Here Z = -100 cm and Z = 1000000 cm, while Z = 0 and Z = 200000 cm. The initial vacuum layer is therefore 100 cm deep.
From these bodies, the following regions (to be assigned a specific material) are defined:
* black hole 1 5 1 -2 * vacuum at the beginning 2 5 2 3 * water layer 3 5 2 4 -3 * vacuum at the end 4 5 2 -4 END
The black hole will be the 1 region: the space contained within body n. 1 (SPH) and outside body n. 2 (RPP),
The inital vacuum will be region no. 2: the region of space internal to volume n. 2 and below the XYP plane defined as n. 3.
The water volume will be the region of space (the 3 region) internal to volume n. 2 and delimited by the two XYP planes.
The 4 region, defined at the bottom boundary of the sea-water region, will be defined as a vacuum region.