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analytical or numerical solutions. In order to retain the significant effects that may result from the inclusion of exaggerated nuclear motion, some characteristics of a typical plasma core reactor will now be considered. The introduction of a model of such a reactor allows physical arguments to be used in making simplifying assumptions. For purposes of describing the nucleonic characteristics, the reactor is basically a central region of uranium plasma surrounded by a cylindrical annulus of hydrogen coolant plasma. To provide the desired neutron reflection while operating at high temperatures, the reaction chamber is assumed to be graphite. The determination of the neutron energy spectrum for this model is of primary importance, since all nuclear characteristics of the system will be directly affected by the neutron spectrum. The simplest case to consider is the zero power plasma core reactor which consists of a critical mass of uranium plasma surrounded by graphite. No hydrogen coolant is included since there is no significant heat production at zero power. For an adequately reflected zero power reactor, leakage is assumed to be negligible. For a high power rocket reactor, leakage due to neutron streaming through the nozzle would have to be included. The neutron spectrum in the zero power reactor will be determined by scattering collisions with graphite and uranium, and by absorption