Neutron Resonances in the kev Region: Heavy Even Elements

Neutron cross-section curves as a function of neutron energy have been measured for Se(1-80), Sr(6-102), Zr(2-80), Mo(1-80), Ba(15-102), Ce(5-55), and Pb(2-80); the energy range in kev of each curve is shown in parentheses. The number of peaks observed are 8, 4, 11, 9(?), 5, 12, and 10, respectively. Isotopic assignments of a few of the observed resonance peaks are ${\mathrm{Se}}^{80}$; 3 and 7 kev; ${\mathrm{Sr}}^{88}$; 15 and 95 kev; ${\mathrm{Zr}}^{90}$; 43 kev; and ${\mathrm{Ce}}^{140}$; 24 kev. No doubt many peaks, particularly those due to minor isotopes, have been missed completely. It is concluded that many of the nuclides which make up these complicated isotropic mixtures would be found to have strong, well-separated resonances if they were measured in an isotopically pure state with a neutron energy spread of the order of a few kev.