What is a plausible way to have a micro-scale containment system that prevents excited nuclear isomers from decaying?


A nuclear isomer is an excited state of an atomic nucleus. This is energetically mid-way between chemical energy and what we normally consider nuclear energy.

log scale cartoon

178m2Hf for example stores 2.446 MeV per atom, compared to over 200 for Uranium fission. Adding a bar for 1 330 000 MJ/kg to the above chart (the bar will be 260 m tall), we see that even at 1% of nuclear levels it's about 10,000× more energetic than any chemical energy.

A grain of sand is about 10 mg. A single milligram is microscopic speck. One milligram of this isomer would have the same power as 10 grams of chemical explosives, about the same as a grenade or anti-tank projectile.


The excited nuclear isomer is used as an explosive in small projectiles, ranging from ultra-fine needles to fléchettes. The ammo will be stored in small hand-held guns.

engineering problem

Given a near(ish) future with nanotechnology, superconductors, and the like, what is a scientifically plausible device that can store the excited nuclear isomer?

The containment system must prevent the excited isomer from decaying. If the specific isomer used has a long half life, we also have the opposite requirement of inducing such decay over the entire sample on command. If the natural half-life is sufficiently short, than simply turning off the containment will make it explode as all atoms release their energy within a small fraction of a second.

The physical system must be miniaturized to sub-millimeter dimensions. Since nanotechnology is available, you just need to have the physical principles involved realizable in a small number of atoms and without large cavities.

Supplemental equipment can be in the gun, with the system on the projectile only needing to last on its own for the time of flight.

some food for thought

quantum Ζήνων effect, Bose-Einstein condensate, relativistic time dilation, induced gamma emission.

BEC applicatitivity asked on Physics.

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    $\begingroup$ Excellent! Glad to see a question on nuclear isomer explosives. Plus one for the cool conception. $\endgroup$
    – a4android
    May 28, 2017 at 8:32
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    $\begingroup$ I know it's a good question when I have to do some supplemental reading just to decide whether it's above my pay grade or not. :-) $\endgroup$ May 28, 2017 at 10:31
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    $\begingroup$ I suggest relativistic time dilation can be taken off the menu for some food for thought. Considering most nuclear isomers decay within nanoseconds it would take excessively high levels of relativistic time dilation. Nuclear isomer explosives would be moving at such high relativistic velocities their kinetic energy would exceed their explosive yields by very large orders of magnitude. Throwing anything at those velocities would be just as deadly. Really, that's a pity. $\endgroup$
    – a4android
    May 28, 2017 at 13:21
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    $\begingroup$ This is a fine question. It might be a good one for the physics stack. I have never heard of anything that could alter the rate of nuclear decay. I suspect what you would have to do is avoid exciting the isomer until you needed it. $\endgroup$
    – Willk
    May 28, 2017 at 20:14
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    $\begingroup$ @JDługosz To boil down the question a bit... you are essentially asking: "I postulate a semi-magic concept somewhat grounded in physics. Can I then assume that another semi-magic concept — needed for the first one to work — is plausible?". Answer: yes. Since you have already wandered into the realm of semi-magic, any semi-magic concept you wish you use is plausible. $\endgroup$
    – MichaelK
    May 29, 2017 at 6:47

3 Answers 3


(Note: I'm not a physicist...)

Other than by relativistic effects, there is no known way of delaying or stopping the decay of nuclear materials, so we should choose nuclear isomers that are stable. This would allow us to have a weapon that isn't spent by the time we need to use it, having emitted all of its energy in the form of high-energy radiation in the meantime.

Thus, we would choose nuclear isomers with long half-lives (something with a half-life of 10 years would decay by 50% in 10 years, thus becoming only half as potent). If we assume that the usable lifespan of a weaponised nuclear isomer ends once it decays to 90%, then the lifespan is 15% of its half-life (=log2(100/90)). Thus, if we want to be able to store the material for 5 years, the material would need to have a half-life of over 33 years (5 years/15%).

The problem is that nuclear isomers that are stable will still slowly decay due to the normal stochastic (random) process rather than spontaneously. That's the same problem that the Manhattan project had. In their case, they overcame that by inducing a neutron cascade that triggered the fission process across the entire sample of material.

For a nuclear isomer, a similar trigger mechanism would be to bathe the material with radiation of specific frequencies to decrease the spin states of every atom so the material as a whole will undergo explosive decay. The radiation required would depend on the material chosen, ranging from gamma rays down to microwaves.

To achieve this, the casing for such ammunition would be designed to serve multiple purposes: a) to hold the projectile together; b) to convert a safe form of radiation (e.g. radio waves) into radiation of the triggering frequencies; c) to prevent the radiation caused by the natural decay process from getting out by absorbing the photon and re-emitting it at a lower frequency (heat or radio waves or even light). The explosion could then be triggered either remotely (by directing a beam of radiation at it) or locally by having an emitter built into the projectile to create the triggering radiation at the right time. The latter would require a smart projectile, either with sensors built in to detect proximity to target, or at least a timing mechanism, with the delay programmed into the projectile by the gun prior to firing.

Given the half-life requirements, following nuclear isomers would be suitable:

  • 166m1Ho (Half-life 1200 years => Usable weapon life 180 years; 6 keV photon emitted = ~578 MJ/mole = ~3500 MJ/kg)
  • 178m2Hf (Half-life 31 years => Usable weapon life 4.6 years; 2.3 MeV photon emitted = ~221,600 MJ/mole = ~1,250,000 MJ/kg)
  • 180mTa (Half-life >1015 years => Usable weapon life >1.5x1014 years; 75keV photon emitted = ~7,200 MJ/mole = ~40,000 MJ/kg)

All of these have much greater specific energies than TNT (=4.6MJ/kg), so you can pick whichever you feel would work for your scenario. The 178m2Hf has the greatest energy available, at about 270,000 times more energy than TNT, but the others aren't too shabby; 166m1Ho has 761 times more energy than TNT with 180mTa having 8700 times more energy than TNT.

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    $\begingroup$ So your answer is to use a long-lived isomer and cope with normal decay rate (as opposed to preventing the natural decay), and use “some form of radiation” to trigger bulk decay. Right? $\endgroup$
    – JDługosz
    May 30, 2017 at 7:05
  • $\begingroup$ Yes. In this case, it seems to be easier to trigger a reaction than to delay decay indefinitely. You could postulate some mechanism that allows you to delay decay (e.g. by manipulating the spin states so that the spin goes up instead of down), but you would still have the issue of making the whole material sample decay at once (or at least within a few nanoseconds) explosively, rather than over years/decades/millennia/aeons as natural radioactive decay. $\endgroup$
    – Pak
    May 30, 2017 at 11:39
  • $\begingroup$ You should explain that in the post. As written it’s mostly talking around tne question and my summary in the first comment was all the relevant meat I found in it. $\endgroup$
    – JDługosz
    May 30, 2017 at 20:43
  • $\begingroup$ On the point of "there is no known way of delaying or stopping the decay of nuclear materials", Hypothetically (and this is VERY hypothetical) if you gave me a magical substance that was a perfect mirror for alpha particles, and allowed me to create a box on the scale of an alpha-particle wavelength using this substance then I could enclose an atom and stop it decaying (suppress the density of states). The problem is that this material doesn't exist. $\endgroup$
    – Dast
    Nov 19, 2021 at 11:44

Isomer Bomb


With the right Isomer, it may be possible to induce a very violent and rapid decay by blasting it with gamma rays. This may be a viable method for trigger an explosion using Hafnium which has been looked into. Your weapons could consist of a primer that triggers a blast of gamma rays into (insert isomer here) resulting in the rapid decay. Put in a casing that can help focus the decay products to continue the reaction. This may or may not be how some nuclear weapons work.

With advances in particle physics, it may be possible to engineer elements/isomers that fit the needs required. On a similar note, a universe I'm working on has an extremely advanced civilization using a stable-ish Hassium isomer in kinetic weapons because of its very high density, predicted to be ~40 g/cm$^3$.


Since an isomer is a metastable nucleus, that is to say, kept from decaying because its constitute parts have just enough extra energy to hold together and that decay occurs when that energy is released. Therefore, it might be possible to store the isomer in an environment that constantly keep the nucleus on the perturbed. I imagine a scenario where the isomer is stored under gamma ray illumination, the energy of the decaying isomer is replaced the flux of extra gamma radiation. This would only be practical if the decay chain has several steps in it, otherwise, the gamma radiation would be better suited as the weapon itself.

  • $\begingroup$ I wonder if you’re confusing fission with the relaxation of the excited nucleus that I’m interested in. “Hold together, constituent parts.” $\endgroup$
    – JDługosz
    May 31, 2017 at 1:43
  • $\begingroup$ In your second part, you are saying that the same conditions used to trigger decay will instead prevent decay. Supplying gamma radiation of the energy needed to excite the nucleus, the same as emitted when it relaxes, will actually cause other atoms to relax! That is due to a property ob Bosons and is how a laser works. $\endgroup$
    – JDługosz
    May 31, 2017 at 1:53
  • $\begingroup$ That may very well be, however fission is a decay mode of larger events. $\endgroup$ May 31, 2017 at 1:57
  • $\begingroup$ For the second part, that's why there is a question mark there. I was envisioning a metastable system where the incident gamma radiation provides just enough excitation to keep the nucleus together. I do however agree with your assessment. $\endgroup$ May 31, 2017 at 1:58

All right. let's see:

  • Near-relativistic time dilation: The projectile would vaporize you before it even exits the barrel.
  • Zeno's arrow: You have to measure the stuff (isomer density decrease in the projectile), so you're place energy into the system == overheating + need of constant power supply ((further decrease in isomer density to allow for these structures)
  • Bose-Einstein condensate: maybe, but still too complicated.


  1. Inducing gamma-ray emission in more stable isomers with high power photons, similarly to lasers.

  2. Using isomers to trigger an uncontrolled fusion by focusing enough gamma-radiation on deuterium = pure fusion bombs.

  3. Using nuclear isomers to create a gamma-ray laser cannon.

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    $\begingroup$ Cancer inducing? I would expect a weapon to kill quickly... not after years.. $\endgroup$
    – L.Dutch
    Jun 8, 2017 at 2:35
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    $\begingroup$ Thanks for answering! This post is in the “very low quality” review queue, though. It doesn’t make a lot of sense, and seems to be alusions to your previous (deleted) answers. I think you are trying to avoid the problems with the earlier answer posts by just stating your result and leaving off the “in-character” writeup. However, this has two problems: ① now it's a couple non-seqitors. With no explaining, the “ascended” statement makes no sense, other than as a reference to the deleted post. … $\endgroup$
    – JDługosz
    Jun 8, 2017 at 7:49
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    $\begingroup$ And, the “real deal” is just dropped in without any reasoning. ② the previous posts were not ill-received only because of the in-character narration. They were not answers! “no, you don’t want that; do this instead!” is not an answer to the question. Your gamma-ray laser post was not a misplaced 4chan or redit post in terms of writing style, but still was dowvoted and flagged as not an answer. So repeating the ideas in another try, even if you had presented them well, is not going to work. I hope this helps. Let me point out that there is an Answer Sandbox you might use. $\endgroup$
    – JDługosz
    Jun 8, 2017 at 7:55
  • $\begingroup$ Here is the link to the Answer Sandbox on Meta that @JDługosz mentioned. It hasn't been used much as far as I can tell, but that doesn't mean we can't revive it. $\endgroup$
    – Secespitus
    Jun 8, 2017 at 9:26
  • $\begingroup$ Even if this is an answer to the question, I can't tell how it is. $\endgroup$
    – user
    Jun 8, 2017 at 12:26

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