放射 ほうしゃ せい崩壊 ほうかいじゃありませんでした
hōshaseihō kaija arimasendeshita

Noun
Desu Copula

The polite, past negative form of 放射性崩壊

1. Was not radioactive decay.; Wasn't radioactive decay.

Past/Perfective
Negative
Polite
Terminal Form