After the war, the department returned to obtain particular successes thanks to the return to Italy of many influential personalities. In 1949, lectures were given by the Nobel laureate Enrico Fermi, collected by the assistants of the universities of Rome and Milan, and were then published in 1950 by the Accademia Nazionale dei Lincei. In 1952, Giuseppe Occhialini, who returned to Italy, taught higher physics and founded the Laboratory of Cosmic Physics and Related Technologies of the CNR and the Astrophysics Section of the Physics Department of the University of Milan. Here he creates a leading school in the research of cosmic rays with the use of nuclear emulsions exposed at high altitudes, an experience that culminated in 1954 with the G-Stack experiment. He also founded the Space Group, so called because it conducted high altitude observations with stratospheric balloons first, then with rockets and finally with artificial satellites. It is also through these activities that Italy and Milan have quickly acquired positions of excellence in the field of High Energy Astrophysics and more particularly in X-ray and Gamma-ray astronomy. To allow this type of activity, Beppo Occhialini also took action on the organizational level, founding various sections of various research institutes still present, and taking charge of both the theoretical and experimental direction of the department.