So, in the process of developing a magic system, I have come up with an ability and I don't know why any mage would want to use it. Basically, some mages can control radioactive decay, and what that means is that they can cause radioactive decay of a particular substance within an object to speed up or slow down, increasing or decreasing it's half-life, but in the process they have to cause the half-life of that same substance somewhere else to change in the opposite direction so that, overall, the half-life of a particular substance remains constant within the universe. Nonetheless, despite this limitation, what this means on a local level is that they can make materials using Nuclei, atoms, and most importantly quantum particles that would normally be unstable.

The only thing I am having a hard time with is figuring out why they would do this? Sure, there are some applications, like reducing the ambient radiation from Radon emissions on earth to globally lower cancer rates, but would a magician from midaevil times even think of something like that? Sure, they could hypothetically capture muons, somehow combining them with Nuclei, keeping those muons stable and make new muonic chemicals and alloys (while simultaneously setting off random explosions who knows where), but aren't atoms with Muons instead of Electrons more prone to fusion due to their small size? Or do I need non-decaying Tau particles to turn your average Baguette into death, the destroyer of worlds? Even if it isn't ridiculously explosive, wouldn't it atleast be heavy?

My mages, these alchemists, have the ability to make absolutely massive arrays of magical substances that we could only dream of, but is there any reason to suspect that a normal fantasy society would use 2nd and 3rd generation materials in any practical application or are the practical uses for this kind of power really bound to the modern and space age of my world?

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    $\begingroup$ I don't think you can apply particle physics to such a speculative system and let it make sense. The ability to cause decay to speed up is used in literally every Atomic bomb and nuclear reactor. That's not anything special. Radioactive decay is a statistical property. You can make it happen really fast, which results in a nuke. As for applications, i mean you tell me why a Mage with the ability to cause nuclear explosions isnt useful in any context ? $\endgroup$
    – ErikHall
    Aug 16 at 6:38
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    $\begingroup$ @ErikHall Sorry, a nuclear chain reaction doesn't change the decay rate of the fissile material, it induces fission by tossing a lot of neutrons around the condensed material. It's the neutrons slamming into nuclei that cause the fission rate to rise, not anything changing the natural fission rate. $\endgroup$
    – Zeiss Ikon
    Aug 16 at 11:08
  • $\begingroup$ You might find Greg Egan's notes on the novel Scale to be useful. $\endgroup$ Aug 16 at 17:53
  • $\begingroup$ @ZeissIkon, I'm not sure that this is an absolute, because magic. The magic might increase decay by reducing the stability of the nuclei. If that's the case, neutron bombardment would definitely induce further decay, creating aforementioned chain reaction. You're right, though, that directly inducing decay wouldn't have that effect. $\endgroup$ Aug 16 at 18:01
  • $\begingroup$ @RobertRapplean Yes, magic might do that in the questioner's situation -- I was specifically referring to the comment above mine. $\endgroup$
    – Zeiss Ikon
    Aug 16 at 18:07

3 Answers 3


This question is very close to a hypothetical “What would happen if…”. What type of world are you trying to create? Are you telling a story? Is this particular magic needed to tell that story or make it more interesting? If it is not important, but an aspect of a large system which must be included to make logical sense, you can just sort of ignore it and state that mages do not use it due to the harm it causes. Manipulating radioactive decay is dangerous and would likely cause illness and death. If the magic is needed for your world to function properly, you should have an idea as to how it needs to be used to move the story along. Just because it can be used in a specific manner does not mean it will be. Alcohol can be burned to produce light, but people still tended to make it to drink instead of burn. People need to see its utilization as practical and useful.

The fact that radioactive decay can be halted is an amazing ability. It means that historically dangerous materials can be handled safely. Can these materials be “locked” into a specific state (i.e. continuously emitting radiation at a higher rate without the constant attention of a mage)? Certain substances would still be impossible to hold in a non-decay state due to the speed at which the element decays. When you are dealing with a half-life of yoctoseconds there is not enough time to capture a stable element, nor would other elements of the same type be able to provide any sort of buffer due to the rapid nature of their decay. Although… that could be a reason why in your world that certain elements decay so quickly. Their stabilized forms are so useful, and used so heavily, that the rest of the universe believes they decay extremely rapidly.

That being said, we can look at the history of mankind to determine likely avenues of utilization. Aside from the detrimental health impact of ionizing radiation, the primary outcome of decay is heat. In a medieval/fantasy type setting, heat is one of the most important elements in society. Heat was used to warm homes, cook food, smelt metals, and for warfare. Lead metal has been used for thousands of years and makes excellent radiation shielding. I could see it being combined with radioactive materials to make heating bricks for warming homes and ceramic walled ovens with iron grill plates for food preparation. There are limitations due to the low melting point of lead and its toxicity, but there is another element which is great for shielding and perfectly safe… gold.

Gold melts at 1.06K C, which means heat from it could be used to smelt tin, zinc, lead, aluminum, and even silver. Bath/steam houses could utilize gold radio-heat bricks for water heating. A small gold radio-heat sphere could potentially be added to a cooking pot and used as a heat source instead of burning wood. Cooking without fire would be revolutionary. Not only did gathering firewood take time and energy, but trees needed to be seasoned prior to use, which takes time. Enough of a stockpile needed to be gathered to last through wintertime to prevent needing to gather firewood in the cold. Smoke has a detrimental impact on the local environment. Creosote buildup in chimneys can cause fires which devastated entire towns. Medieval cities often relied on shipments of wood from distant locations. Crops and foodstuffs were grown near cities when possible. This meant that the land was cleared of trees to make way for fields. Cities built near rivers could sometimes rely on upriver logging efforts to supply their wood demand. Removing firewood as a main fuel would be a game changer.

Depending on your world’s metallurgic technology level, Osmium would make for excellent shielding and has a melting point of 2.92K C, which would allow for the smelting of iron, steel, copper, nickel, titanium, gold, platinum, chromium, and cobalt.

The use of this magic in warfare depends heavily on the range. Can a mage effect radioactive material a kilometer away or merely arms-length? The ability to control radioactive decay would likely result in the study and understanding of how quickly the various radioactive substances heat up, and for how long they can sustain various levels of heat. Knowing that, and the average travel time of a catapult/trebuchet projectile, it could be used to create radioactive firebombs. Radioactively “salting” of fields and other important locations could render them effectively dead until a mage comes in to neutralize the decay and the radiation decreases to a safe level. I could even see handheld (or platform-based) radiation projectors being used by mages to irradiate enemy soldiers. Siege warfare would be severely affected by such capabilities. Arrows with small amounts of radioactive material embedded could become extra dangerous, starting fires, irradiating impaled persons, or even irradiating a location for area denial. Adding lead to armor would likely be a necessity.

If your mages can make magics which pale in comparison to the utilization of radioactive decay, it could be seen as a “poor man’s” magic. People who cannot afford the safe alternative would turn to the cheaper option.

  • $\begingroup$ You could just use an alpha source. No shielding required. Gamma and beta sources are witchcraft and will get you baked at the alpha stake! $\endgroup$
    – g s
    Sep 6 at 18:37

Blow up uranium

Or at least overheat it.

Presume, a mage has discovered that there is a substance with a half-life nearby, upon investigation it turned to be an uranium-rich ore deposit. That mage has managed to procure some of pure uranium, placed it somewhere away and decided to make its half-life down to 0.5 seconds. The next thing he knows is he's flying head over heels, and the uranium has turned into a mushroom cloud. Recognizing its potential as a super-weapon, siege or whatnot, the mage has started a covert investigation of what he could do, and how hard it would blow up. In the meantime investigating the aftereffects of that blow yielded that employing those fissile isotopes won't do squat, so the mage cleaned up by forcing them to rapidly decay, probably being protected by a layer of ground.

Eventually altering uranium's half life would yield various small-yield uranium-powered heaters aka mini-nuclear power plants, with mere micrograms of accelerated U-238 that would last several seasons, or surprise assassinations made by the same principle but turned over9k. Say, the half life of U-238 is some 4e9 years, a mage that would accelerate a sample's half life to 1e-6 seconds would produce a "magical" nuke of controlled power, possibly just enough to wipe the target without eliminating the entire city. Since increasing half-life does not cause major troubles for whoever is not using the affected uranium, and that it could be extended to infinity without actually changing a lot, this action could be pretty much accounted for as "free", yet there should be an upper limit of U-238 to be blown up like that. Still, there's also U-235 with a lot smaller half-life that also produces neutrons for chain reaction, so the actual alterations with enriched uranium could take even less, but blowing up depleted uranium should still be doable.

Accelerating C-14

The same principle applies, if a person's C-14 content would all decompose, they would suffer like being exposed to severe levels of ambient radiation, but since the exposure would be totally internal, the consequences would be worse, down to outright death of a victim. Quite some implementation of half-life magic.

Exotic matter is too unstable to be of any use

You considered muons - but their half-life is about 2e-6 seconds, extending their half-life to years or higher would take quite a toll over the universe, even if there is enough muons in various processes across it to satisfy the requirement of "retain half-life of total substance". This would actually limit the amount of exotic matter to about 1e12 atoms at 1Y half life, which is too low to be of any practical use.

Considering other semi-stable isotopes - well, maybe you could gain some use of Co-60 or a similar gamma source, or Radium as an alpha source, yet they are already usable, and for the big BOOM uranium looks like the best candidate; other implementations are way away from medieval.


Long term storage of fissile materials

Obviously, your mages are going to be using thier powers to kickstart the atomic age... but the problem with nuclear anything is that it tends to involve leaving a bunch of radioactive stuff around. From your fuel rods to your spend waste, you have all these safety hazards and none of the modern technology we have for controlling and disposing of them. This is where slowing down decay comes in. When you have unused fuel rods, instead of needing a special containment facility to keep them from melting your face off, you just spread the decay effect out over an entire lake or something so that the radiation levels in any one spot are tolerable.

Then you just reverse the process when you are ready to use your fuel. Furthermore, you nuclear mages don't need to understand all the things we use to regulate nuclear reactions like salts or carbon rods, because thier magic itself regulates the decay rate so that makes understanding all the tricky math and chemistry behind nuclear science a lot less important. You just slow/speed the decay to whatever you need it to be.

Lastly, when you are done with a fuel, you can just put the radiation in your reactor room on hold while you walk in, replace the fuel rods with your bare hands, and toss out the old rods which you can also stabilize.


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