In Hiroshima, there are permanent shadows caused by the intensity of the blast from the bomb that was dropped. Nuclear bombs emit EM(electromagnetic) radiation which was absorbed by the people or objects that were in front of the radiation. So if they were far enough away from the blast, they wouldn’t have been incinerated, but still would have cast a shadow.
Since thermal radiation is light, and since light travels from a central point, everything in its path is burned except when there is something blocking it, so it creates this shadow effect. The surfaces behind the matter (the objects you see the shadows of) received much less radiation bleaching so there is a visible difference