放射
ほうしゃ · housha · JLPT N1 · noun
radiation
☢️ 放 (release) + 射 (shoot): things released outward, like light or rays shot out from a source
放 means let go or release; 射 means shoot or fire. Radiation is energy shot outward from a source, and 放射 is the same idea: something released and sent out in all directions.
放 — 方 (square/phonetic) + 攵 (rap/strike radical)
放 is a semantic-phonetic compound: 方 supplies the sound and 攵 (a hand holding a stick) supplies the meaning of striking or driving away. The original sense was to banish or drive out, which broadened over time to 'release', 'let go', and 'put down'.
射 — body 身 + inch/hand 寸
Originally a pictograph of a hand drawing a bow with an arrow. The ancient form showed 弓 (bow) plus 矢 (arrow) or a hand. Over time it was reshaped into 身 (body) plus 寸 (hand/measure), and the meaning 'to shoot' was extended to 'emit' or 'project'.