When to meet senesce?

什么时候会开始衰老？

Chillness intensified the senesce of leaves, enhanced the MDA content and the O2-. produce rate, this was more evident in Shanyou63.

低温处理加剧了叶片的衰老，使得MDA含量和O2-产生速率上升，两优培九的升幅较汕优63小。

But hang on -- how do we know that radioactive atoms don't senesce?

但是，听清楚了—我们怎么知道放射性原子不衰老？