from the fact that it has the highest thermal fission cross section (thousands of barns), about 10x the next highest cross section across all known isotopes. The 242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of 239Pu. It has a very high cross section for fission, and if in a nuclear reactor is destroyed relatively quickly. Another report claims that 242mAm can sustain a chain reaction even as a thin film, and could be used for a novel type of nuclear rocket. Since the thermal absorption cross section of 242mAm is very high, the best way to obtain 242mAm is by the capture of fast or epithermal neutrons in Americium-241 irradiated in a fast reactor. However, fast spectrum reactors are not readily available. Detailed analysis of 242mAm breeding in existing pressurized water reactors (PWRs) was provided. Proliferation resistance of 242mAm was reported by the Karlsruhe Institute of Technology 2008 study. Italy In 2000, Carlo Rubbia at CERN further extended the work by Ronen and Chapline on a Fission-fragment rocket using 242mAm as a fuel. Project 242 based on Rubbia design studied a concept of 242mAm based Thin-Film Fission Fragment Heated NTR by using a direct conversion of the kinetic energy of fission fragments into increasing of enthalpy of a propellant gas. Project 242 studied the application of this propulsion system to a crewed mission to Mars. Preliminary results were very satisfactory, and it has been observed that a propulsion system with these characteristics could make the mission feasible. Another study focused on the production of 242mAm in conventional thermal nuclear reactors. Current research in the US since 2000 Current solid-core nuclear thermal rocket designs are intended to greatly limit the dispersion and break-up of radioactive fuel elements in the event of a catastrophic failure. As of 2013, an NTR for interplanetary travel from Earth orbit to Mars orbit is being studied at Marshall Space Flight Center. In historical ground testing, NTRs proved to be at least twice as efficient as the most advanced chemical engines, which would allow for quicker transfer time and increased cargo capacity. The shorter flight duration, estimated at 3–4 months with NTR engines, compared to 6–9 months using chemical engines, would reduce crew exposure to potentially harmful and difficult to shield cosmic rays. NTR engines, such as the Pewee of Project Rover, were selected