probably the most realistic one on pt
Hiroshima: 15kt, Nagisaki: 21kt.
The "Fat Man" bomb dropped on Nagasaki on August 9, 1945, had the nuclear charge, 6.4kg of plutonium (Pu-239), only the shooting mode of your save, that is similar to the bomb "Little Boy" that yes had load 64kg of uranium (U-235).