请教两个英语术语：radiation 和irradiation有何异同?

adiation
n.
放射,辐射; 发射; 发光
放射物; 辐射线[能]
散射器
【生】辐射形;【测】射出测量法;【医】射线疗法
语义扩展; 语义推演
irradiation
n.
放射,照射
阐明,启发; 启迪
【物】光渗; 光线; 辐照[射]
【医】照射
扩散
这样看不出来什么区别吧?
其实通俗一点讲 虽然两词都有照射的意思 但是radiation是 "主动"的发出照射的一方,而irradiation强调 "被动"被照射的物体,那个被照射的也可以说是 have been irradiated.
Radiation is emitted from something and travels from its point of origin to somewhere else.
When radiation hits something else (and is therefore stopped) the thing that has been hit is said to have been irradiated.
举个例子
A sunbather is undergoing irradiation by radiation emitted by the sun.