out of curiosity: how far away must the source of such a pulse be to be survivable? what is the "minimum safe distance" beyond which the gamma density is low enough to permit survival?
See this:
http://www.bautforum.com/archive/index.php/t-11239.html
It really is a complicated question. Lethal dose is 450,000 millirem, but we don't (as far as I know) have an accurate way of determining the radiation field mathematically.
Suffice it to say, I wouldn't want to be within, oh, a couple of hundred million miles of an event like this without some amazing shield technology.