I have a group of time wizards (who only use time magic) who are attacking a country that just underwent a massive magical industrial revolution. These wizards are terrorists and they have a spell that can rewind 100 kg of lead into a piece of uranium with equivalent mass. The spell can reach 30 feet and has obvious incantations and arm movements, but magic is common so most people won't give it a second thought. How do they use this spell to cause as much panic as possible in this society?

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    $\begingroup$ This is greatly dependent on what kinds of magical counter-measures are available. Do these people even understand what uranium is? I'm guessing that to them it's just a toxic metal. Slow poisoning is rarely a dramatic frightening thing unless it's widely advertised. That lump of metal isn't going to be fissionable, even if it is uranium. $\endgroup$
    – DWKraus
    Commented May 21, 2021 at 12:50
  • $\begingroup$ The question comes across as somewhat story-based at present, is there a way you can clarify to include more details and make it clear what the exact worldbuilding problem that needs solving is? $\endgroup$ Commented May 21, 2021 at 12:52
  • $\begingroup$ 100kg of 100% U235 wouldn't be supercritical (think you need compression for that), but it would certainly melt down in a very big way. Probably too quickly and too dangerously to escape, but if they're willing to do the suicide bomber thing... then again, in a preindustrial society that is vaguely Europeanish, I'm not sure that there are any great concentrations of lead to zap. $\endgroup$
    – John O
    Commented May 21, 2021 at 13:18
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    $\begingroup$ Also, since only part of lead comes from uranium, you may not have a very enriched block. Your uranium will be embedded in natural lead, which will help shield it. reddit.com/r/askscience/comments/20bqp0/… $\endgroup$
    – DWKraus
    Commented May 21, 2021 at 13:30
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    $\begingroup$ What isotope of uranium does the spell transform the lead into: U238, which is toxic but mostly stable, or U235, the very fissionable kind? A quick Google says that around 100kg is just over twice the critical mass for U235 so launching the spell from less than a couple of kilometers away instantly nukes the caster along with the target. (The transformation must also be instantaneous; anything less will result in a fizzle as the transformed mass melts itself apart.) Below the critical mass, the transformed sphere just heats up into a very radioactive molten puddle a la China syndrome. $\endgroup$ Commented May 21, 2021 at 14:18

4 Answers 4


Any element has unstable isotopes which are radioactive. That might be what you want to consider in addition to or instead of changing the element.

Uranium has a long half life meaning it is relatively less radioactive than other radioactive elements. More radioactive elements, those with shorter half lives, are Radium and Radon which result from Uranium's decay.

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So for your story you might consider turning lead into Radium or Radon gas which would be much more deadly.

Terrorist weapons (we might consider chemical and biological weapons to be such) are concerned with delivery. So Radon gas might be a means of delivery.

  • $\begingroup$ Also consider that uranium oxide, which has a glowing orange color and radium which has a glowing green color have been used as jewelry. This is not an answer for your question but will help describe the appearance in your setting. $\endgroup$ Commented May 24, 2021 at 12:38
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    $\begingroup$ @DavidR said that polonium would be good for my purpose so I'll probably use that. $\endgroup$
    – MrHiTech
    Commented May 24, 2021 at 12:39
  • $\begingroup$ You've hit it! I didn't think to check what the intermediates between uranium and lead are. Yes, stopping at polonium, radium or (if you can avoid being collateral damage yourself - remember the spell's range is only 30 feet) radon would give MUCH scarier results. $\endgroup$
    – A. B.
    Commented May 26, 2021 at 10:09

I am assuming that your time magic works be reversing the flow of time around a piece of lead so that it reverts to its previous form, uranium. This means you will end up with natural uranium (i.e. the distribution of isotopes is the same as that as found in the Earth crust). By far the most interesting thing I have learned researching questions for this site is this:

Health effects of natural and depleted uranium are due to chemical effects and not to radiation.

I was all ready to write about alpha particles and replicating the effects of fallout, but apparently all of that is off the table. The dangers of natural uranium are almost entirely chemical, which means that the molecular form and method of uptake are the most important factors (this source used for everything below). Since there is no way for the terrorists to aerosolize their uranium (at least none that I can think of), they are forced to rely on people ingesting the uranium.

By far the most damaging compounds of uranium when ingested are soluble. Fortunately (or not depending on your point of view), uranium ore, specifically carnotite, is soluble, so even if your terrorist-wizards don't know much about chemistry they have access to toxic uranium compounds. Fortunately (or not depending on your point of view), there have been no human deaths attributed to oral exposure to uranium, and concentrations that could kill rats were so high they refused to eat the food until a sweetener was added. Even if you did get someone to ingest uranium despite the clearly horrible flavor, the effects would not be significant:

A volunteer given a single dose of 1 g uranyl nitrate (14.3 mg/kg) and observed for clinical signs and symptoms within 24 hours after intake suffered acute nausea, vomiting, and diarrhea within a few hours of administration. All clinical signs returned to normal within 24 hours after administration of the oral uranyl nitrate dose (Butterworth 1955).

Uranium compounds can also cause a lot of kidney damage, and in a place without access to modern medicine this could be fatal, but I don't think it would be useful to terrorists. For uranium concentrations to be high enough that kidney damage can cause death in your context, there is no way to cause uranium poisoning except through force feeding, which is way harder to do than simply stabbing the target.


It sounds like you are running time backwards to get the original element. But what is the original element???

First, as has been pointed out, not all the lead came from uranium in the first place.

Second, where did the uranium come from? Wind it back far enough and you have hydrogen. Makes a big boom if you let it mix appropriately with the atmosphere and then light it.

Or lets not go quite as far back. The s-process (slow neutron capture) hits a wall at Polonium (you have to go from Po-210 to Po-215 before you have any chance of going higher and the half lives of everything above Po-210 are measured in microseconds at best.) Thus your uranium must have come from r-process (rapid neutron capture) in neutron stars. Anything that can bridge that wall at Polonium is fast indeed--and it's not going to stop at uranium. You're going to have a hellish brew of later row 7 elements if you wind every atom back to it's highest state. (And how are you picking just how far back to wind it??)

While you're not going to get an atomic boom out of it some of that stuff is very hot indeed--lethal radiation for anyone nearby.

This will be occurring in the outer layers of neutron stars--I doubt anyone knows how much mixing there is between the atoms on the surface and the neutron soup beneath but since the atoms keep changing there must be some mixing. I have a hard time picturing not having a decent number of free neutrons in the brew--not that big a deal directly but you're going to get neutron activation of whatever is around. The radioactivity of uranium is irrelevant, this is not.


Turn the lead in the church roofs into uranium.

This is assuming they've discovered that uncontrolled exposure to uranium makes people sick. You're talking about a period before the discovery of radiation and its effects.

However most societies of the time were deeply religious and lead is a common roofing material. If the act of going to church makes you sick it's going to cause significant social trauma.

That's assuming these aren't suicide mages.

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    $\begingroup$ But does uncontrolled exposure to metallic uranium tens of meters away really make people sick? $\endgroup$
    – AlexP
    Commented May 21, 2021 at 13:52
  • $\begingroup$ @AlexP eventually, it's a long game. The most devout will get sick fastest. $\endgroup$
    – Separatrix
    Commented May 21, 2021 at 14:20
  • $\begingroup$ The density of uranium (18.95 g/cc) vs lead (11.35) is different; they'll definitely notice when the lead roofing shrinks by about 40% in volume. Plus natural uranium isn't all that radioactive and fissile uranium would give itself away by heating up. $\endgroup$ Commented May 21, 2021 at 14:29
  • $\begingroup$ @GrumpyYoungMan, depends how good your mages are, if they can get that only on the thickness of the plates nobody is going to notice. In terms of isotopes, I'm assuming a naturally proportioned mix, they're mages not nuclear engineers. It will increase background radiation to a point of long term toxicity and high cancer rates, not instant death of radiation poisoning. $\endgroup$
    – Separatrix
    Commented May 21, 2021 at 14:36
  • $\begingroup$ The uranium is much harder than the lead, and will crack and break due to thermal expansion while restrained to the mountings the much more pliable lead sheets were affixed to. When the workmen try to repair it, they will notice the substitution immediately. This will cause people to believe that the church got cursed, leading to religious unrest, leading to chaos. As for radiation? A long chain of alpha and beta emitters, dangerous if swallowed or breathed in, but who is likely to breathe in the "lead" of church roofs? At a distance of 35cm in air, the radiation is absorbed completely by air. $\endgroup$
    – PcMan
    Commented May 24, 2021 at 6:20

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