Complex sentence: He became head of the Metallurgical Laboratory's chemistry section in January 1942, and in March, his small experimental reactor using beryllium came closer to criticality than the graphite-moderated design of Enrico Fermi's group at Columbia University.
Split into simpler sentences: He became head of the Metallurgical Laboratory's chemistry section in January 1942. In March, his small experimental reactor using beryllium came closer to criticality than the graphite-moderated design of Enrico Fermi's group at Columbia University.