This is the fifty-fourth progress report of the Laboratory for Nuclear Science at the Massachusetts Institute of Technology. Progress reported covers the period for Physics and Chemistry through April 30,1959. Progress is reported on: (1) Chemistry of the fission elements group, (2) Nuclear chemistry (inorganic) group, (3) Nuclear chemistry (organic) group, (4) Cosmic ray group, (5) High energy accelerator physics group, (6) Bubble chamber group, (7) Liner acceleratory group, (8) Rockefeller generator group, (9) ONR generator group, (8) Radioactivity group, (9) Cyclotron group, (10) Theoretical group, (11) Personnel listing.

Results of an initial examination of non-fuel-bearing materials for the Marine Gas Cooled Reactor are presented. Areas given specific attention include structural and cladding materials and graphite moderator. Other areas not included because of classification include zirconium hydride moderator and control materials. In each report section, available pertinent information is summarized and a plan for future work is given.