SetFactory("OpenCASCADE");
Box(1) = {0, 0, 0, 1, 1, 1};
Sphere(2) = {0.5, 0.5, 0.5, 0.2};
BooleanDifference { Volume{1}; Delete; }{ Volume{2};}
Physical Volume("Matrix",9) = {1};
Physical Volume("Particle",10) = {2};