Does everything become radioactive if bombarded with radiation for long enough?

Especially, say, concrete or lead. If something highly radioactive goes on inside a room lined with concrete or lead, and this goes on for many decades, will the walls of the room themselves eventually become radioactive as well?

If so, is there any material that never becomes radioactive no matter how long it is exposed to radiation?

It depends on the kind of material and the kind of radiation. High energy electromagnetic radiation (X-ray and gamma ray) will cause materials to become ionized (e.g. have electrons in elevated or free energy states) and will emit more ionizing radiation. Alpha, beta, and particularly neutron and heavy ion radiation can cause elements to transmute either by absorbing the particle and fusing or becoming an unstable isotope, or spallation by adding too much kinetic energy and causing an atomic nucleus to fragment. This can happen with really high energy gamma rays, too, though photodisintegration but the particle energies have to be really high, like those found in a supernova.

Just bombarding an arbitrary substance with low energy radiation, e.g. shining a flashlight on a rock will not cause it to become radioactive, and even directing X-ray or low energy alpha particles will not cause most materials to emit radiation beyond the infrared (in response to heating up). But if you shine a neutron source on any material for long enough you’ll see some level of transmutation as neutrons are absorbed as every material has a definable neutron absorption cross-section. However, producing the unstable heavy isotopes of helium under normal conditions is very, very unlikely and they decay almost instantly, so in practice they are never seen outside of a particle accelerator.


For realistic energies, the only way to render something radioactive is with neutrons. And for most purposes, the only way to get neutron radiation is from fission. So the containment vessel for a nuclear reactor, for instance, might become radioactive, but a vault containing a bunch of radium won’t.

What’s more often a worry is contamination. That’s where you’ve got bits of dust and the like made out of the already-radioactive material, and it gets all over something else. In principle, this can be cleaned off in the same way as any other kind of dust, but depending on what it is that got contaminated, and how nasty the contaminant was, you might not be able to do a good enough job of it.

Perhaps what OP is thinking of–if not, I am–is the case where someone is exposed to radiation over s length of time (pilots/nuclear reactor workers) potentially dangerous to health or demonstrably clinically so, and the Geiger counters on them registers over the red line (clicks high, in movies).

ETA: IE, exposes to the kind of radiation described previously but now that I mentioned it, non contact (laser) IR thermometers would be fun to fuck around with at a summer beach.

Again, there are different types of ionizing radiation. Gamma rays/x-rays/high energy ultraviolet (high energy photons) and to a lesser extent beta particles (energetic electrons) can do damage via external exposure, and alpha particles (charged helium nuclei) and energetic heavy ions (heavier charged atoms) can do damage if ingested, and specifically damage to the genome, interrupt cellular function, and damage to the immune system and intestinal biome (gut bacteria) but will not cause materials to become activated (transformed into radioactive isotopes) and emit more radiation under normal terrestrial circumstances. Only neutron bombardment or absorption of radionuclides will cause someone to emit radiation via atomic decay.

A Geiger counter detections ionization that is a result of active radiation but does not detect passive exposure to radiation. So, if you have alpha or beta particles on your person it will detect those being released, but it cannot measure how much you have been exposed to gamma radiation, for instance. Pilots and other air crew are exposed to ionizing radiation from space due to the reduced protection in spending time above the thickest part of the atmosphere including heavy ion bombardment but most of their exposure is gamma radiation, either directly from space or due to spallation of heavy ions off the upper atmosphere producing secondary radiation. The aluminum skin of an airliner, while thin, is sufficient to stop virtually all alpha and beta particles.

The biggest terrestrial exposure to radiation (aside from skin damage due to ultraviolet or X-rays in occupational exposure) is ingestion of natural radon gas trapped in underground environments, ingestion of naturally radioactive materials from excavation and mining residues (particularly pitchblende, monazite, and thorianite) from uranium and rare earth extraction, and the processing and enrichment of nuclear fuels and synthetic radionuclides for medical, detection, and weapon applications, e.g. enriched uranium, plutonium, americium, et cetera. Nuclear power plant workers are rarely exposed to such materials because the fuel elements themselves are delivered already encapsulated in protective cladding and are handled remotely; their biggest risk is exposure to secondary sources of radiation due to activation of reactor hardware and the inner coolant loop to neutron radiation, and great care is taken in design and operation to minimize those exposures. In a properly working reactor, workers are exposed to less occupational sources of radiation than they are to that in the ambient environment. At far greater risk are workers who work in fuel enrichment and fabrication facilities and the general communities around them, e.g. the massive contamination of the Savanah River facilities, the Cimarron Fuel Fabrication Site that was the focus of the Silkwood v. Kerr-McGee lawsuit, and numerous other enrichment and fabrication facilities around the world, which is the reason the United States currently has only one working domestic facility for large scale commercial nuclear fuel production.

Virtually everything you see in films about radiation exposure is at least misleading and often completely wrong, particularly the idea that there is some precisely quantified magical threshold of exposure time to “radiation” that you can inch right up to but not exceed without any ill effects. The impact of exposure to different types and levels of radiation has a range of effects on different people and tissues or organs. Some modes of exposure can have immediate effects but little in the way of correlated long term impact, and some have a clear cumulative impact but high variability, and there are still things we are learning about exposure in space to solar and high energy cosmic radiation (such as its long term effects on the cardiovascular system, the immune system, and the gut biome) that are still poorly understood over the long term.


The easiest way for a person to “become radioactive” would be for them to ingest in some way some material that was already radioactive. Swallow a gamma source, and there will be gamma rays coming from your stomach. Or, if you don’t consider the contents of your stomach to be part of you, then make it food containing carbon-14, or breathe oxygen-18, or something, so the radioactive material gets incorporated into your tissues.


Unfortunately the “Banana equivalent dose” is nothing but an amusing teaching tool.

Potassium Homeostasis would make your excretions mildly higher risk as P-40 is a tiny fraction of the potassium in a Banana anyway. If you eat a lot of bananas or not, living near large quantities of your urine probably isn’t a grand idea anyway.

You might be confusing two things: a Geiger counter, which measures radiation coming off of something at that moment, and a dosimeter/badge which measures how much radiation has already hit the badge.

If the person comes out of the reactor room, and a Geiger counter held up next to them goes crazy, that means they’ve been contaminated with bits of the radioactive reactor fuel. They need to wash/dispose of their clothes/etc so they don’t track plutonium dust everywhere (their body is not radioactive; it’s just got plutonium dust on it).

If the person comes out of the reactor room, and their dosimeter is showing a big red skull and crossbones, that means that while they were in the reactor room, they got a (too) large dose of radiation. Depending on how large a dose, they’re looking at a range from an increased risk of cancer to imminent death.

Those two things are independent; you could be contaminated without having gotten an overwhelming radiation dose (though if you don’t decontaminate, the dose will keep increasing), or you could get a huge dose without getting contaminated (and could get a huge dose from a situation where contamination isn’t possible).

One claim that is sometimes (often?) made is that irradiated food will be radioactive. I assume that this is nonsense. A colleague of mine built a harpsichord in his office that happened to above a cyclotron and was convinced that the harpsichord had become radioactive. He finally convinced someone to test it with a geiger counter and it showed only background.

Brazil nuts.

Food is irradiated using ionizing radiation which has enough energy to strip some electrons but not enough to create a super villain.

The X-rays, Gamma or electron beams they use would be dangerous, but not the material that is exposed to it.

Exposure to Ionizing radiation is what poses the risk, not the irradiated food but the word “radiation” is scary, especially if you don’t have a hard understanding that heat and light are also “radiation”. While not ionizing radiation, sitting inside the oven while you cooked a roast would pose a health risk too and is technically radiation .

The analogy to cooking is particularly apt: Cooking serves the same purpose as food irradiation; to kill germs. And heat, like ionizing radiation, is dangerous: You certainly wouldn’t want to be inside of an oven. But that doesn’t mean that food that’s been exposed to radiation or heat is necessarily dangerous. If anything, food irradiation is safer than cooking, because food that’s been exposed to heat can be dangerously hot for a short time after it’s removed from the heat source, but irradiated food is safe the moment you turn off the gamma gun.

So when the KGB slips some polonium into your tea, you’re going to set off that Geiger counter because the radiation source is inside your body, and there’s no way to remove it. But if you sat on a polonium chair you would wouldn’t set off the Geiger counter afterwards, even though you might have already absorbed a lethal dose of radiation.

I thought that, in principle, alpha sources were not that dangerous until actually swallowed. But you might still avoid the red-hot, blue-glowing glowing polonium chair (which is impossible to make out of solid polonium anyway).

To be fair, it’s even harder to make a chair out of liquid polonium.

Nah, swallowing is not needed. They’re typically even more dangerous if inhaled- for example, Radon gas.

Skin will stop alphas, though.