Eli5: what happens to contained radation during neclear decay?


If I put a radioactive thing in a lead box, as it decays, where does the radiation go? It can’t leave the box, but conservation of energy means it can’t just vanish. After the object isn’t radioactive anymore, would the air in the box be radioactive/dangerous now?

Eta: can’t edit the title, sadly. *radiation

In: 1

The radiation given off by a decaying radioactive object is called ionizing radiation. This radiation is powerful enough to knock electrons off of atoms, creating ions. When the object stops decaying, the radiation it emits is much weaker and no longer considered ionizing.

The radiation given off by a radioactive object is contained within the object as it decays. However, as the object decays, it also gives off heat. This heat can cause the object to glow, and the radiation can escape from the object in the form of light.

If a radioactive object is placed in a lead box, the radiation will be contained within the box. The lead box will absorb the radiation and prevent it from escaping. As the object decays, it will give off heat, but this heat will be contained within the box.

After the object has stopped decaying, the air in the box will not be radioactive. However, the lead box may be radioactive if it has absorbed radiation from the decaying object.

The energy in the radiation is attenuated by collisions with the lead atoms. The reason that radiation is so damaging to life forms is because of its ionizing potential; it has enough energy to strip electrons from an atom, which plays all kinds of hell with biological processes. Lead is dense enough, and has enough electrons to spare, that it can provide shielding from ionizing radiation in a relatively compact form; lead has a “tenth thickness” (attenuates radiation to 10% of its former value) of around two inches.

The short answer is the box heats up. “Containing” radiation just means capturing the high-energy particles that are being emitted. This depends a bit on the type of radiation, but the general principle is the same. High energy particles can do damage to people, particularly to their DNA. Once that energy has been captured and spread out (heating up the radiation barrier), it’s no longer all that dangerous.

“Radiation” as a property making something radioactive isn’t necessarily conserved. Sometimes the particular form of radiation will make whatever it hits convert into a radioactive isotope. But eventually everything decays into stable isotopes.

Radiation is an emission. In the case of gamma rays, it’s basically light. That light travels out until it hits something and is absorbed. Removing the radiation source from the box, like flipping a light switch, removes the radiation.

While the source is in the box, it constantly produces radiation and that radiation is constantly striking the edges of the box being absorbed.

Radiation isn’t contained by shielding. It’s blocked by shielding.

At a fundamental level, radiation is individual energetic particles. When they encounter material, they’ll either pass through without interacting or give up some of their energy when they interact with the particles of the shielding. Any radiation stopped by the shielding has simply given up all it’s energy to the shielding material and heated it up.