FYI ... some more references:
The Curse of the Demon Core
http://www.neatorama.com/2011/11/28/the-curse-of-the-demon-core/
The Manhattan Project’s Fatal “Demon Core”
http://www.physicscentral.com/buzz/blog/index.cfm?postid=8146939447898984108
The Demon Core
http://talesfromthenuclearage.wordpress.com/2009/11/26/the-demon-core/
www.orau.org/ptp/Library/accidents/la-13638.pdf is heavy but fascinating reading of all the criticality accidents all around the world, especially including the US and the Soviet Union, but also elsewhere. It’s dry and technical, but includes excerpts of interviews and (doomed) people’s notes aware of their own fate. It also includes reconstructions of what happened, in detail. Very technical, but fascinating to those inclined to such things. It’s also very long, to the tune of hundreds of pages.