// Define a parameter for later use
:P POSZ 5.

// Define materials
:ELEM Hydrogen H 1. 1.
:ELEM Oxygen O 8 16.
:ELEM Nitrogen N 7 14.
:MIXT Air 1.214E-03 2
      Nitrogen   0.75
      Oxygen     0.25

// Define rotation matrix
:ROTM R00 90. 0. 90. 90. 0. 0.  // unit matrix

// Define volumes and place them
:VOLU world BOX 30. 30. 30. Air

:VOLU "my tube" TUBS 0. 10. 20. 0. 360. G4_WATER
:PLACE "my tube" 1 world R00 0. 0. $POSZ

:VOLU sphere ORB 5.  G4_AIR
:PLACE sphere 1 "my tube" R00 0. 1. 10.