In an elastic collision the neutron loses part of its kinetic energy to the nucleus with both the kinetic and momentum of the system being conserved. However, for many elements the scattering is not isotropic in the center-of-mass system at the higher neutron energies. Many of the present reactor multigroup codes include anisotropic scattering at the high neutron energies, while many others assume isotropic scattering at all energies. In order to consider some of the effects of including anisotropic scatting, reference is made t the multigroup equation generally assumed for the slowing-down density.

The information concerning beryllium assembled herein has been selected primarily to provide information that might be pertinent to the design of the ART. The creep-rupture data in the literature have been obtained from vacuum cast and extruded beryllium, rather than from the hot-pressed beryllium which will be used in the ART. A research program is being conducted by the Brush Beryllium Company, under contract to the Oak Ridge National Laboratory, which will eventually provide the design engineers with data on the high temperature strength properties of hot-pressed beryllium. In the interim, it will be necessary for the metallurgists and design engineers to make judicious estimates and extrapolations from the data available.

Short reports to the members of the Nuclear Cross Section Advisory Group from three groups: (1) High voltage group; (2) Fast chopper time-of flight spectrometer; and (3) Electronuclear research division.

In order to test the operation of a freeze jacket in air with the process fluid closely following the conditions found in the high pressure circulation loop of a homogeneous reactor, or, 2000 psi and 300C, a test loop was built and used in conjunction with existing refrigeration equipment. The freeze jacket was made of 5/16-in. type 346 stainless steel tubing wrapped around and welded to a 1/2-in. stainless steel process line. It was concluded that for these reactor operating conditions, only a small leak rate, 11 cc/min, could be frozen off. It is recommended that, at the beginning of the the freezing operation, the temperature of the secondary refrigerant entering the freeze jacket be at least -40C and that the freeze jacket be made as long as practical.

It is the purpose of this memo to clarify and revise burnup calculations for the APPR irradiation program and to present a proposed irradiation schedule. the report will also be in the nature of a review of the program.

A method for calculating the frequency response of weighted voids (proportional to reactivity of steam voids) as a function of reactor power is presented.