Measurement and Interpretation of Neutron Total Cross Sections of Carbon, Calcium, and Lead

The neutron total cross sections of carbon, calcium, and lead have been determined in the energy region 200-960 kev using a time-of-flight technique. The observed cross section for carbon has been analyzed in terms of the effective-range theory as well as the bound-level contribution, with results which agree very well with those obtained by the ($d, p$) stripping experiments. Also it is concluded that the upper limit for the total width of the "proposed" resonance in ${\mathrm{C}}^{13}$ at 610 kev is 100 ev. For calcium and lead the data are analyzed for resonance parameters. It is found that the $s$-wave strength function for ${\mathrm{Ca}}^{40}$ increases rapidly with increasing energy. It is concluded also that the course of the Pb cross sections can be explained only by the presence of a broad $s$-wave resonance in ${\mathrm{Pb}}^{208}$, at $E_n=515\mathrm{}\pm 15$ kev with a neutron width ${\Gamma }_n=100\mathrm{}\pm 15$ kev.