Status of Six-Group Delayed Neutron Data and Relationships Between Delayed Neutron Parameters from the Macroscopic and Microscopic Approaches

Work performed in part for an American Nuclear Society Standards Committee Subgroup (ANS 19.9) to assess the status of delayed neutron data is summarized. Recent measurements of delayed neutron emission conducted at Texas A&M University are also described. During the last 10 yr, there have been advances in nuclear data libraries (e.g., improved fission product yields) that make it possible to quantitatively predict delayed neutron emission from basic data. The six-group delayed neutron data available in the literature from both macroscopic level experiments and microscopic level calculations for several actinide isotopes are compared. Results are also presented from recent experimental measurements of delayed neutron emission and delineates some of the relationships between these measurements and microscopic level predictions. For example, from the experimental measurements, Keepin's delayed neutron group 1 is shown to correspond mainly to a single isotope, ⁸⁷Br, as expected from microscopic level theory, and Keepin's group 2 is shown to correspond to primarily two separate isotopes, ¹³⁷I and ⁸⁸Br. In the future, it may be useful to use properties of specific isotopes to replace Keepin's delayed neutron groups 1, 2, 3, and 4 for prescribing delayed neutron data for actinides.