Elastic and Inelastic Scattering of Fast Neutrons

Abstract

Cross sections for the combined processes of absorption+inelastic scattering of fast neutrons ($E>~4.5$ Mev and $E>~7$ Mev) have been measured for a number of elements by the use of absorbing cylinders and aluminum or iron detectors. A smooth increase with increasing atomic number is found. For neutrons of energies \ensuremath{\ge}7 Mev the ratio of these cross sections to the cross sections for absorption+total scattering (Dunning) is nearly constant at a value of about 0.4. The existence of a scattering of fast neutrons in which little or no energy is lost has been demonstrated experimentally and approximate cross sections for the process have been obtained. Cross sections for an "effective absorption" of medium fast neutrons have also been determined. These cross sections, which are smaller than those obtained for the faster neutrons mentioned above, show a maximum at about $Z=50$ and a marked decrease for the heaviest elements. The cross sections obtained by Aoki and Lea from experiments on the yield of gammarays from the action of fast neutrons on matter are in agreement with the present results.