Status of six-group delayed neutron data and relationships between delayedneutron 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 summari zed. Recent measurements of delayed neutron emission conducted at Texas A&M University are also described. During the last 10 yr there have been advan ces in nuclear data libraries (e.g., improved fission product yields) that make it possible to quantitatively predict delayed neutron emission from ba sic data. The six-group delayed neutron darn available in the literature fr om both macroscopic level experiments and microscopic level calculations fo r several actinide isotopes are compared. Results are also presented from r ecent 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 dela yed neutron group I is shown to correspond mainly to a single isotope, Br-8 7 as expected from microscopic level theory, and Keepin's group 2 is shown to correspond to primarily two separate isotopes, I-137 and Br-88. In the f uture, it may be useful to use properties of specific isotopes to replace K eepin's delayed neutron groups 1, 2, 3, and 4 for prescribing delayed neutr on data for actinides.