Experimental techniques are described for the spectral measurement of a collimated fast neutron beam. A hydrogen filled cloud chamber, proton recording nuclear plates, and threshold fission foils were used as neutron detectors in the measurements. As an application of the above technique, the energy distribution and absolute flux of the fast neutron beam emerging from port 5W of the Los Alamos fast rector has been measured from 0.1 Mev to 18 Mev. The result show a spectral curve possessing a maximum between 9.25 and 0.30 Mev and having an exponential decrease at energies above 1.5 Mev. The mass energy of the distribution is at 0.55 Mev and the slope of the exponential section is 3.1 - 0.1 Mev per decade of intensity decrease.

A new method to procure RaLa sources was proposed by Group CMR-10, Los Alamos Scientific Laboratory. This method depended upon irradiation of small-diameter U235 wire in the Materials Testing Reactor, Arco, Idaho. A procedure for cladding and sealing U235 wire in stainless steel tubing, by drawing, plugging the tube ends, and welding, was developed, tested, and proved to be satisfactory.