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Using the method of weighted residuals, a detailed numerical study is made of the neutronics of spherical cold neutron sources composed of liquid hydrogen and liquid deuterium in reactor moderators of light water, heavy water and graphite, Particular attention is paid to the physical effects at the cold source boundary. The computations allow a number of conclusions to be made on the best designs of spherical cold source configurations. It is found that for small spherical sources there is little difference in neutron gain using either normal-hydrogen or para-hydrogen, and that the largest gains are obtainable from large deuterium-filled sources.

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PACS. 72.15R -Quantum localization. PACS. 05.45 -Theory and models of chaotic systems. Abstract. -The energy level separation distribution of a fermionic disordered many-particle system is studied. For a non-interacting system, a crossover is observed from a Wigner (GOE) distribution for the frst and second excitations to a different form which depends on the number of particles for low-lying excitations and then to a Poisson distribution for high excitations. This behaviour also holds for weakly interacting systems, while for stronger interactions a transition of the high excitations to a Wigner distribution is observed.