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### Geant4 volumes hierarchy

There are three types of volumes in Geant4 , and can arrange them in order to build a recursive hierarchy, or a tree, that defines the detector. They are organized as the creation process of a detector component.

- Base volume: it is the pure geometrical definition of a detector component. For example, a box, a cylinder, a polyhedra ...and the dimensions i.e. it is the component project on paper.
- Logical volume: it is the definition of the detector component obtained combining the geometric definition and the material, i.e. it is the component at the exit of the workshop.
- Physical volume: it is a logical volume that recieved a placement (center position vector and space transformation like rotation, translation ...) in a mother volume, i.e. it is the component introduced in the detector.

The mother volume of a physical volume is always a logical volume, expect for the main physical volume, which is the ``World'', the experimental hall volume. Therefore, a recursive hierarchy is possible. A physical volume C will be put in a logical volume B, at a certain position and with a certain orientation. The physical volume B will be the placement of the B logical volume (including the physical volume C) into a logical volume A, and so on.

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