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Since the main purpose of this example is to describe the technicalities of interfacing the HBOOK routines, we shall not consider a sophisticated geometrical description and we shall limit ourselves to the simple approximation of a single large volume uniformly filled by water having homogeneous properties. This can be easily obtained using a Rectangular Parallelepiped body (RPP) with one edge parallel to the propagation axis (Z).

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 different materials.

We remind here that all physical regions 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 external boundary of this 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_min and Z = Z_max such that Z_max – Z_min = Depth, where Depth is the desired thickness of water. The extreme Z coordinates of the RPP body, Z₁ < Z_min and Z₂ > Z_max, will be chosen so that Z_min – Z₁ and Z₂ – Z_max 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.

Figure 1: Sketch of the geometrical setup of the current example. The size of the bodies is not in scale.

The bodies can be defined in the geometry data cards (free format with names) according to the following lines:

SPH LARGESPH   0.0 0.0 0.0 5000000.0
RPP WORLD      -1000000.0 1000000.0 -1000000.0 1000000.0 -100.0 100100.0
XYP SEATOP     0.0
XYP SEABOT     100000.0
END

Here Z₁ = –100 cm and Z₂ = 100100 cm, while Z_min = 0 and Z_max = 100000 cm. The initial and final vacuum layers are therefore 100 cm deep.

From these bodies, the following regions (to be assigned a specific material) are defined:

* black hole
BLACKHOL     5  +LARGESPH -WORLD
* vacuum at the beginning
VACTOP       5  +WORLD +SEATOP
* water layer
SEA          5  +WORLD +SEABOT -SEATOP
* vacuum at the end
VACBOT       5  +WORLD -SEABOT
END

The black hole will be the 1^st region (named BLACKHOL): the space contained within the body LARGESPH (SPH) and outside the body WORLD (RPP).

The initial vacuum will be the region #2 (named VACTOP): the space within the body WORLD (RPP) and above the XYP plane named SEATOP.

The water volume will be the 3^rd region (named SEA): the space within the body WORLD (RPP) and delimited by the two XYP planes (SEATOP and SEABOT).

The 4^th region (named VACBOT) is at the bottom boundary of the sea-water region SEA (within the body WORLD (RPP) and below the XYP plane named SEABOT) and will be defined as a vacuum region.

Giuseppe Battistoni; INFN, Milano
Francesco Cerutti; CERN, Geneva

Last updated: 10th of December, 2008