Hacker News Reader

Comment by fragmede | Hacker News Reader

My hot spoon isn't made up of uranium and didn't come out of a nuclear reactor, and isn't radioactive, so I'm not sure how that addresses GP's concerns.

View on HN

Your hot spoon is in fact radioactive, emitting thermal radiation. Thermal radiation doesn't make things it hits radioactive. Neither does your microwave oven or even gamma radiation. Radioactivity can be induced in things by neutron radiation, but not EM radiation. It is safe to eat food which has been irradiated with gamma radiation, and chances are you have many times before (it is fairly common for dried spices and herbs to be irradiated for preservation purposes.)

Things that emit thermal radiation are not radioactive. An easy way to conceptualize it for stuff here on Earth is that radioactivity involves stuff flying out of the nucleus of an atom, while other forms of radiation do not.

Thermal radiation is in fact emitted from the nucleus of atoms; all matter emits black body radiation. The reason hot things generally aren't considered radioactive is because that would pull literally all matter into the discussion.

But that wasn't the point being made here. The point being made with the hot spoon example is that EM radiation doesn't make other things radioactive (except insofar as it heats things up). This is equally true of gamma radiation as thermal radiation. Thermal radiation and gamma radiation can both cause harm directly, but neither will make other things radioactive.

That's why it's completely safe to eat food that was sterilized with gamma radiation intense enough to kill you outright.

I think you may be confused about the distinction between radioactivity and black body radiation. The fact that gamma rays, microwaves, visible light and so on are all on a spectrum doesn't mean that every EM emitter is radioactive.

Whether or not you want to apply the term "radioactive" to a black body emitter is completely beside the point, which is that EM radiation doesn't make things radioactive. Your objection is to the use of a word, not the physics, so I think this discussion has run its course.

At high enough photon energy, electromagnetic radiation actually can make things radioactive. The general term is "photonuclear reactions."

Here's an example:

"Photonuclear production of medical isotopes 62,64Cu using intense laser-plasma electron source"

https://aip.scitation.org/doi/10.1063/1.5100925

Reply on news.ycombinator.com