Radiation
noun, する verb
It releases and shoots out of the bomb. It's not fire. It's radiation, and it sticks around a long time once it has been released.
ほうしゃ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
放射冷却のせいで今朝起きた時はものすごい冷え込みだったよ。
It was very cold when I got up this morning because of radiational cooling.