The Effects of Uncertainties in Attachment Rates on EMP Calculations

The semi-analytical EM computer code, MODELC, has been used to study the effect of different attachment rates on the fields that are calculated in the source region and in the free field region. These calculations indicate that changing from the attachment rates published by Longley and Longmire to those based on more recent measurements made by Price and van Lint can lead to differences in peak fields of the order of 25%. Late time fields will be even more severely affected, and differences of 50% in the electric fields there can be seen. For the late time fields, two other sets of attachment rates are considered, based on the review of attachment data by Grover and Gilmore. These other curves represent limits on attachment rates, and calculations using them indicates that the very late time fields may vary as much as a factor of two between the fields calculated with the lowest and the highest attachment rates.