void geom_example(){

  gSystem->Load("libGeom");
  
  TGeoManager *geom_example = new TGeoManager("geom_example","geom_example.C");
 
  TGeoMaterial *mymat = new TGeoMaterial("BERILLIUM",9.01,4,1.848);
  mymat->SetUniqueID(   5);

  TGeoMedium *mymed = new TGeoMedium("BERILLIUM",3,5,0,1,10,2,0.1000000E+11,0.2163378,0.2000000E-03,0.2261152E-01);
  
  TGeoRotation *myrot = new TGeoRotation("myrot",10,20,30);

  TGeoVolume *TOP_VOL = gGeoManager->MakeTube("TOP_VOL",mymed,0,210,350);
  TOP_VOL->SetVisibility(0);
  
  TGeoVolume *CONE = gGeoManager->MakePcon("CONE",mymed,0,360,12);
  ((TGeoPcon*)CONE->GetShape())->DefineSection(0,-124,0,6.55);
  
  gGeoManager->SetTopVolume(TOP_VOL);
  TOP_VOL->AddNode(CONE,1,gGeoIdentity);
  TOP_VOL->AddNode(CONE,2,new TGeoCombiTrans(0,0,-131.5,myrot));
  gGeoManager->CloseGeometry();

  gGeoManager->GetTopVolume()->Draw("ogl");

}