Semi-empirical modifications of age theory have been made to interpret the critical masses of proton moderated assemblies, which may or may not have reflectors of various substances, in particular, water or steel. Section I shows that critical masses of untamped water moderated systems can be calculated by use of an appropriate age and linear extrapolation length. Assuming that all captures and fissions take place at thermal, a familiar expression can be set up which contains the age and extrapolation length which are not well determined by theory. An age value suggested by theory, (Sec. II) is taken and ORNL criticality data (K343) are used to find the best extrapolation length. With these values the K343 critical mases can be computed to bout +-5%, which is their estimated experimental uncertainty; this for H/U-235 atomic ratios between 43 and 755. Section II contains a theoretical discussion of effects which the simple "theory" of Sec I neglects. It is indicated that several of these effects compensate to make a simple theory more useful than one would believe at first sight. to take into account reflectors of water, water shield by cadmium, or steel of various thicknesses, it proves sufficient to alter the extrapolation …

The angular distribution of fission fragments from the neutron-induced fission of several isotopes has been studied. Distributions were observed for thermal neutrons on U233 and U235, Lady Godiva leakage neutrons on U235 and U238, and 14 Mev neutrons on U233, U235, U238, Th232, and Np237. No anisotropy was observed for thermal neutron fission, whereas for Lady Godiva neutrons and 14 Mev neutrons the probability of fission along the axis of the neutron beam was determined to be higher than for fission in the orthogonal direction. Experimental results are given on pages 10 and ll.