The planet I've built was at one point inhabited by a society of somewhat advanced (think late 1800s) humanoids. Earth-people came to the planet in their first attempt at universal conquest, but ended up leaving after a rebellion from the other people. The Earth-people took all of their things and detonated some sort of nuclear weapon (?), which devastated the population and changed the landscape.

Several hundred years after this, the society puts itself back together. While they do not have their own means of space travel, occasionally people from more advanced societies will stop at this planet. These off-worlders experience some kind of sickness due to the high levels of radiation on the planet.

Question: Is there any theoretical weapon that would leave a harmful amount of radiation in the planet for several hundred years?

  • $\begingroup$ When worldbuilding the only restriction are those you choose to impose on yourself. So unless you have some specific reason why people would experience sickness due to a high level of radiation it's feasible for that to happen in your world. Is there some specific concern you have that's preventing you from just saying "Offworlders run the risk of radiation sickness."? As written it's hard to see why you asked the question in the first place. $\endgroup$
    – sphennings
    Apr 8, 2022 at 19:15
  • $\begingroup$ Closely related: worldbuilding.stackexchange.com/questions/183568/… $\endgroup$
    – Willk
    Apr 8, 2022 at 19:17
  • $\begingroup$ @sphennings was just wondering if "radiation sickness" was the correct condition $\endgroup$ Apr 8, 2022 at 19:22
  • $\begingroup$ As written that's not what your question is asking. You may want to edit your post to more clearly specify what you're asking. If you are asking "Is radiation sickness the correct term for someone exposed to high doses of radiation?" that may be something that you can easily look up on your own. $\endgroup$
    – sphennings
    Apr 8, 2022 at 20:20
  • 1
    $\begingroup$ I'll just leave this here. $\endgroup$ Apr 9, 2022 at 10:54

1 Answer 1


The Earth-people took all of their things and detonated some sort of nuclear weapon (?), which devastated the population and changed the landscape.

In order to maintain a significant amount of radioactivity after a few hundred years, you might consider salted bomb. These are specially modified nuclear devices which make use of the intense neutron flux generated by a nuclear explosion to transmute some material via neutron activation into some suitably dangerous, suitably long-lived radioisotope.

The most long-lived material considered was cobalt-60 which has a half-life of a bit over five and a quarter years, and therein lies the problem. A bit after 52 years, the radiation will have fallen to less than 0.1% of the starting level. A bit after 104 years, it'll be less than 0.0001% of the starting level.

You want something which is still dangerous after several hundred years. Radio-isotopes which are strongly radioactive lose their radioactivity more quickly. Long-lived radio-isotopes must necessarily be less radioactive. this means that you can't really create a salted bomb that produces dangerous radioactivity several hundred years after detonation. (edit: if you made a lot of salted bombs using nickel-62 cases you might be able to achieve your goal, see footnote)

Instead, what you probably require is something that's not merely a genocidal warcrime but also an instrument to carry your spite down the generations (or alternatively: deny an ecosystem to an opponent who might be capable of building closed life support systems and surviving in them for generational timescales... a trick a mature spacefaring civilization might reasonably have developed). This probably needs to be some kind of nuclear reactor, fuelled up ahead of time and built to operate unmaintained for many decades. It creates a steady supply of deadly radio-isotopes by a continuous process, using up a feedstock of suitably fertile material which can then be reduced to some suitable fine dust and blown into the atmosphere where high-altitude winds can carry it around the planet.

A number of these continuous fallout generators can be constructed and placed in hard-to-access bits of the planetary surface. Disabling the devices might be difficult, and blowing them up would be counterproductive as it could release more radiation in the short term. A clued-up spacefaring visitor would be able to detect elevated levels of radioactivity, identify the offending radio-isotopes, realize they must have an artificial source, and track wind patterns to track them down, and then see about sealing them off and shutting them down with robots.

Fictional spacefaring civilizations are notoriously unable to do this baby's-first-exoplanet-landing routine and will be breathing the air, drinking the water and investigating the orifices and intromissive facilities of the locals for biocompatibility before you can say "how have you people survived this long?".

I want a way to have these off-worlders experience some kind of sickness due to the high levels of radiation on the planet. Is this feasible to do?

Sure. Radiation sickness is depressingly well documented. How it would manifest (and how severe it would be) in non-human species is of course entirely up to you.

If you were interested, wikipedia has a list of radioisotopes sorted by their half-life... the mega and gigasecond decay times are probably the ones you're interested in. Long story short: there are almost no neutron activation products with the required half lives, but there are a few exotic fission products and cosmic ray spallation products that are impractical to produce on a large enough scale.

You're left with Nickel-63, with a half-life of about 100 years which can be made via neutron activation of stable Nickel-62. This is naturally stable, but uncommon on Earth (~3% abundance). Oak Ridge National Laboratory manufacture Nickel-63 from enriched nickel by irradiating it in a research reactor, using the result as a radiotracer. It may be possible to use Nickel-62 as the casing in a nuclear bomb for long-lived, lower-energy salted bomb fallout. It'd still have a quarter of its radioactivity after 200 years, but you'd need to make an awful lot of it to start with. Radioactive nickel is considered slightly less dangerous than some other forms of nuclear waste... notably, you have you ingest or inhale it. Compare with the ambient radiation risk of the high-energy gamma rays released by Cobalt-60. A death factory might be easier to build, and guarantees more radiation over a longer timescale, and that radiation will be continually released into the air instead of being trapped in soil and sediment.

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    $\begingroup$ This is a horrifying idea for punishing a planetary population. I like it. $\endgroup$
    – jdunlop
    Apr 8, 2022 at 23:25
  • $\begingroup$ I really like this idea, plus it would work with the way the land is shaped. There are areas of land where people do not go due to some sort of aggressive architecture and/or signage placed long ago. This could be where these death-machines are located. Truly a horrible idea, but very on-brand for humankind, unfortunately... $\endgroup$ Apr 9, 2022 at 3:59
  • $\begingroup$ The Russians supposedly have as one of their "doomsday devices" a nuclear jet engine built to fly for years and salt the world with radioactive byproducts. According to the movies (I think, my memory has had a ~1000x reduction in the last few years) the US wanted more control, so they worked on the "super-dirty-bomb" to use nuclear material to deny area to an invading enemy, more of the cobalt-60 stuff. Plutonium isn't just radioactive, it is toxic at parts per billion. Strontium acts like the element right able it in the periodic table, calcium, and gets placed in bones when ingested. $\endgroup$ Aug 22, 2022 at 13:59

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