It is usual to determine the density of neutrons by using foils of metals which become radioactive as a result of bombardment in the region under investigation. From the rate of disintegration of the newly formed radioactive element the number of neutrons absorbed can be calculated. By use of the capture cross section of the element of which the foil is composed the density of the neutrons can then be computed. By counting the alpha particles from a bismuth foil of known weight after exposure to neutrons the density of the neutrons which produced this activity can be calculated. The least accurately known value which enters into this evaluation is the capture cross-section of bismuth for pile neutrons. This value may be improved by future measurements. It is of importance only for absolute measurements of neutron density so that relative values can be measured with considerable accuracy on the basis of known data.

Report presenting tests on a scale model of a four-engine transport airplane to determine the stability characteristics, empennage control-surface effectiveness, the effect of propeller rotation on longitudinal stability, and a method for carrying spare wing panels under the fuselage. The effect of two models of wing power operation on the characteristics of the model was studied. The results indicate that the model possess satisfactory stick-fixed longitudinal stability for all normal flight conditions except for high power with flaps extended.

Included herein is a historical record of the AAF sponsored NEPA Project during the period of October 1945, to the present time, and covers in narrative form the nature of planning leading to the implementation of the project, the establishment of the operating group and its relationship to the Manhattan District (later to become the Atomic Energy Commission) and the approach to applicable technological problems bearing on both nuclear science and aeronautical propulsion engineering aspects.