The apparatus associated with the Argonne fast neutron "chopper" and techniques that have been developed for its use in neutron transmission measurements are described. Of particular importance is the application of a boron-loaded liquid scintillation counter for the efficient detection of slow neutrons. The nature of the data that are obtained is illustrated by the results given for bismuth, selenium, and manganese. Several techniques for finding neutron resonance parameters and their application to the above data are are discussed. Resonance widths are found for the first two levels in bismuth. For the levels in selenium the measurements give only ${\sigma }_0{\Gamma }^2$. A complete set of parameters is obtained for the first three manganese resonances. The abnormally large ratio of neutron width to level spacing for manganese produces an unusual shape for the cross-section curve in the neighborhood of the second resonance which is interpreted as being caused by interference between the second and third resonances. For this interpretation we obtain $J=2\mathrm{}$ for $E_0=337\mathrm{}$ ev, $J=3\mathrm{}$ for $E_0=1080\mathrm{}$ ev, and $J=3\mathrm{}$ for 2360 ev.

• Received 13 January 1955

DOI:https://doi.org/10.1103/PhysRev.100.126