There used to be a lot of EMP stuff up at DTIC Online, Office of Scientific and Technical Information, OSTI, U.S. Department of Energy, and other places. The Fed had scanned a sizeable chunk of the declassified nuke stuff into .PDFs and put it online, but whole categories got yanked down within weeks after 11 Sept 2001. [searches] at least some of it is back up; go for it.
Most of the reports from Oak Ridge, Sandia, and Livermore are quite readable. There's even some Army stuff out there. I liked the reports of how they determined how close a nuke had to be to take out a pickup truck... instead of "modeling" a result, they just parked a bunch of trucks at different distances, popped a fiery mushroom, and then had some guys go out and see which ones would start and drive away.
Empirical testing at its best!