REGULARITIES IN THERMAL NEUTRON ABSORPTION CROSS SECTIONS.

Thermal neutron absorption cross sections have generally not been considered to show much systematics. However, some regularities are brought out which may not have been stated before. Each stable odd Zi-even Nj nucleus has a higher cross section than the corresponding even Zi - 1-even Nj nucleus, with very few exceptions. The odd Z nuclei show a pronounced cyclic variation in cross section, while the corresponding even Z nuclei have considerably less variation. Justifications for these rules are presented on the basis of the existence of a pairing force in the nucleus. Suggestions are given for additional cross section measurements to be made. These involve the determination of cross sections of stable, as well as, radioactive nuclei. Author