Robot enters Fukushima Daiichi unit 1 containment vessel

[quaker bill]

23. The precise mechanism is barely relevant

An explosion of any sort in a nuclear reactor is always a bad thing. The fact that it was not a nuclear detonation very slightly improves it. Chernobyl was not a nuclear detonation per se, but it was a very bad thing.

There is a thing about radiation and in particular cesium you need to get. It has probably been explained before, but I will give it a whack.

E=MC^2. (Energy = Mass * Speed of light (squared))

What this means to a cesium atom (or any other atom, regardless of source):

Radiation is energy.

For a cesium atom to release energy (read radiation), it must lose mass. Typically in nuclear chemistry this happens when fission occurs. Typically fission breaks an atom into two pieces, sometimes one piece is smaller than an atom, but often two different atoms result. Neither of the two new atoms are cesium, and when you add all the split parts up, there is slightly less mass than there was before fission. This is where the energy in the radiation photon of say a gamma ray comes from. If you can determine the missing mass, you can then calculate the energy of the photon produced using the above formula and determine the wavelength of the radiation produced.

This is called nuclear decay. For any single atom of any species, decay happens once. An atom of a radioactive isotope does not sit there glowing and spewing radiation, it decays, once. Emitting radiation requires a loss of mass and this happens only during decay. After decay, it is no longer cesium. Where the danger of cesium 137 comes in is the short half life, the short half life means that cesium 137, in even very small quantity, say a million atoms or so, will produce a lot of individual nuclear decays in a short time.

It is important to remember how small atoms are. A million cesium 137 atoms will have a mass of 1.37 * 10^-15 grams, a tiny fraction of a picogram. (about a millionth).

Being exposed to ionizing radiation is not a good thing. It does however happen all the time and every day. Our bodies have developed repair mechanisms to deal with it. If they hadn't our lifespans would be far shorter.