Well these effects are all we really have to go on:
"The atomic bomb, nicknamed "Little Boy", which was dropped on the Hiroshima City, exploded at an altitude of 580 meters above a hospital close to
the present A-bomb Dome (the former Hiroshima Prefectural Industrial Promotion Hall) at 8:15 am on 6 August 1945.
The atomic bomb employed uranium-235 and was equivalent in power to approximately 15 kilotons of TNT gunpowder. The dissipation of energy is believed
to have been in the following ratio: bomb blast - 50%, thermal rays - 35% and radiation - 15%.
It was estimated that the bomb blast traveled about 3 km, the thermal rays, about 3.5 km, and radiation, about 2 km, from the hypocenter,
respectively. (Figure prepared by Radiation Effects Research Foundation.)"
"The atomic bomb, nicknamed "Fat Man", which was dropped on the Nagasaki City, exploded at an approximate altitude of 500 meters above a tennis
court at Matsuyama-cho of Nagasaki City at 11:02 am on 9 August 1945.
The atomic bomb employed plutonium-239 and was equivalent in power to approximately 21 kilotons of TNT gunpowder. The dissipation of energy is
believed to have been in the following ratio: bomb blast - 50%, thermal rays - 35% and radiation - 15%.
It was estimated that the bomb blast traveled about 5 km, the thermal rays, about 4 km, and radiation, about 2.5 km, from the hypocenter,
respectively. (Figure prepared by Radiation Effects Research Foundation.)"
www.hiroshima-cdas.or.jp...
They probably have created more efficiant bombs since then, but this is really the only working info that we have to go on.