See: http://www.washingtonpost.com/world/national-security/the-b61-bomb-a-case-study-in-needs-and-costs/2012/09/16/494aff00-f831-11e1-8253-3f495ae70650_story.html?hpid=z1
This article has a surprising amount of technical detail, and some close up photos of a 50-year-old bomb and the components in it. - Jed
