目前情况下值得忧虑的是电离辐射，它由重同位素——如碘131和铯137——自发衰变而生成。

Of concern in the current situation is ionizing radiation, which is produced by spontaneously decaying heavy isotopes, such as iodine 131 and cesium 137.

youdao

原子激发态是不稳定的，其必然会自发地向低能级衰变，产生自发辐射现象。

Atom's motivated state in not stable, it inevitably disintegrate into the lower energy state, which makes the phenomenon of the spontaneous radiation.

youdao

原子激发态是不稳定的，其必然会自发地向低能级衰变，产生自发辐射现象。

Atom's motivated state in not stable, it inevitably disintegrate into the lower energy state, which makes the phenomenon of the spontaneous radiation.

youdao