// Define a parameter for later use :P Z_HALF_LENGTH 2.5*cm // Define materials :ELEM Hydrogen H 1. 1. :ELEM Oxygen O 8 16. :MIXT Water 1. 2 Hydrogen 2./18. Oxygen 16./18. // Define rotation matrix :ROTM R00 0. 0. 0. // unit matrix // Define volumes and place them :VOLU world BOX 100. 100. 100. G4_AIR :VOLU "my box" BOX 50. 50. 50. G4_AIR :PLACE "my box" 1 world R00 0. 0. $Z_HALF_LENGTH :VOLU Chamber BOX 5.*cm 5.*cm $Z_HALF_LENGTH Water :PLACE Chamber 1 "my box" R00 0. 0. -$Z_HALF_LENGTH :PLACE Chamber 2 "my box" R00 0. 0. $Z_HALF_LENGTH