Corel Painter. Reference photos were used. The framed pictures are of: Little Boy - 1945, Fat Man - 1945, Trinity - 1945, Oak - 1957. The woman in the chair was also photo referenced, but it is an image I've had saved for a long time - I'm unsure of the original.

Interesting fact time:
"The bombs killed as many as 140,000 people in Hiroshima and 80,000 in Nagasaki by the end of 1945."

Paraphrased:
"The release was uneventful, and the gravity bomb known as "Little Boy", a gun-type fission weapon, took 57 seconds to fall from the aircraft to the predetermined detonation height about 1,900 ft above the city. It created a blast equivalent to about 13 kilotons of TNT. The U-235 weapon was considered very inefficient, with only 1.38% of its material fissioning."

[link]

If that's not considered "efficient," I'm scared to know what is.

EDIT: Holy crap, thanks for the DD! I have another work related to this image on Youtube, for those interested: [link]