JEF-2 DELAYED NEUTRON YIELDS FOR 39 FISSIONING SYSTEMS

There is a need for a more complete and accurate knowledge of absolute delayed neutron yields (<(v)over bar d>). One method to derive <(v)ov er bar d> for a given fissioning system involves a summation calculati on using cumulative fission yields (Cu) and the delayed neutron branch ing ratios (Pn) of all precursors. In this work, we have used for thes e data the recently revised European JEF-2.2 evaluation (Joint Evaluat ed File-version 2.2). We have limited the number of precursors to 158, comprising 100 measured Pn data and 58 calculated values. We show tha t the contribution to the <(v)over bar d> calculation of the unmeasure d Pn values is almost negligible. However, it seems that the new nucle ar mass data may improve the prediction of Pn values. According to our results, the relative uncertainty due to the Cu yields is three times higher than that due to the Pn values. We also present a systematic w ay to derive <(v)over bar d> for exotic fissioning systems. (C) 1997 E lsevier Science Ltd.