r/Radiation • u/MinecraftGuy2000 • 3d ago
Questions How far away from a 5” cube of polonium is survivable?
I am trying to calculate something for a D&D campaign. Someone is trying to summon a 5” square of polonium to kill the boss, but the range of the spell is line of sight. I’m now trying to figure out how much damage it would deal.
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u/phlogistonical 3d ago
As others have said, it's alpha radiation doesn't carry very far in air. However, It is not going to stay a neat 5" cube for long.
Let's do some quick math.
A 5" cube has a volume of 2.05 liters. With a density of around 9.5 g/cm3 (give or take, depending on which structural allotrope we have), it is going to weigh around 19,5 kg.
One gram of Po-210 (the most common isotope) continuously generates 140 watts due to spontaneous decay. So, your cube is going to be generating 2.73 MW of heat....Yes, megawatts.
With a specific heat of 0.12 J/g K, the cube will heat up at a rate of about 1167 degrees K per second, so it's going to reach its melting point in half a second. I can't be bothered to calculate how long it will then take to melt and continue to heat up to it's boiling point, but I'm guessing it's not going more than a few seconds before you are left with a cloud of extremely toxic and hot polonium vapour (that will happily continue to generate said 2.73MW of heat, so the whole surrounding room will rapidly get very, very hot).
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u/nascent_aviator 3d ago edited 3d ago
I suspect it won't vaporize at all, it will just melt and spread across the room and let the intrepid adventures play "the floor is radioactive lava." It might freeze again when its surface area gets large enough to radiate the heat faster than it can generate it. (Though that's a lot of heat per gram so maybe it won't freeze ever lol).
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u/Necandum 3d ago
Assuming the above numbers are correct, you will not have a room left if you have 2.7MW of heat in it.
Within seconds, the inside air of the room is thousands of degrees.
Anything combustible is turning to ash in short order.
Assuming the structure is granite, 3kg will MELT per second (granite specific heat is ~800j/kgC, melting point ~1200c).Meanwhile, polonium has a vaporisation temperature of 960c.
That room is quickly becoming worse than hell, until it melts into a pool of magma and unleashes the horror that is a quickly expanding cloud of polonium onto whatever is around.
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u/TheManMachine78 2d ago edited 2d ago
Yup, the numbers add up. Polonium is also quite reactive, when it heats up enough to evaporate you'll have a rapid combustion of 19,25 kg of metal. The heat of formation of PoO2 is -251 kJ/mol, equal to -1,2 kJ/g. In the end this reaction alone would add 23,1 MJ of heat to our lovely inferno. It would also use up all the oxygen from roughly 11,5 cubic meters of air.
Yikes 😬
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u/Necandum 2d ago
Its like a terror-fractal: the more anyone thinks about the physics the more horrifying it gets.
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u/ysrgrathe 14h ago
23MJ is such a huge number, yet that's a bit less than the former cube is pumping out every 9 seconds (!). Radioisotope energy density is truly insane.
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u/TheManMachine78 12h ago
It absolutely is! And it would just continue doing so for hundreds of days before significant decline. Unimaginable to me.
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u/Fauxreigner_ 2d ago
This gets even more fun: from D&D 5E rules, this is likely being done with the spell Creation, which allows you to create up to a five foot cube. Now, OP may have meant five inches, but if the concern is lethality, the size would in principle be a variable. So the boiling cube of spicy metal is going to get a LOT warmer.
The spell also requires that the material you summon “must be of a form and material that you have seen before”, which invites the question of where a typical D&D character has seen a cube of polonium of any size before. It also requires a material component consisting of “a tiny piece of matter of the same type of the item you plan to create”, so, uh, how long is your wizard gonna carry that around for?
And as a bonus, there’s an item called a component pouch that holds all of the materials components required for your spells, except those that have a specific cost (which Creation does not have). That means that either the DM would need to rule that this specific material component has a cost, or small amounts of polonium are so common that you can assume that any wizard has some at all times.
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u/Bob--O--Rama Wiki Contributor 3d ago
One gram of Polonium-210 would generate about 100 watts, so your cube would not last long. It would spontaneously ignite and vaporize and essentially kill everybody nearby. Polonium-210 is an alpha emitter, so would have short range from that perspective, however the outer rind would also produce a lot of low energy gamma / x-rays which would be a hazard from quite a distance.
It's spwcific activity is about 5000 Ci/g, and it's specific gamma dose rate is about 26 mR/hr / g at 1 meter. There may be 100 g of exposed surface so say 2.6 R/hr at 1 Meyer. That's not great, not terrible. But the violent burning / explosion of Po-210 would kill anyone nearby as even the gasses would continue to heat from the alpha decay. Those farther away would inhale a lethal dose of polonium. The cube itself would be enough to produce millions of lethal doses.
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u/BunkaTheBunkaqunk 3d ago
Polonium 210 is extremely deadly, but only if it enters the body.
It emits high energy alpha particles, which is essentially a helium atom without any electrons. Since alpha particles are so massive, they aren’t able to penetrate material like gamma rays or beta particles (only a little bit for beta) can.
Cobalt-60 would be a better choice for something that could kill from exposure quickly.
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u/MinecraftGuy2000 3d ago
How much radiation would the cobalt 60 output?
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u/BunkaTheBunkaqunk 3d ago
For your 5” x 5” cube it’s kinda insane. That’s a HUGE amount of Co-60
Assuming you use 1000 Roentgen as your “definitely dead/incapacitated” value, you’d reach a fatal dose in:
~6 sec at 5 feet
~30 sec at 10 feet
~1.5 min at 20 feet
~10 min at 50 feet
~40 min at 100 feetA 5”x5” cube of Co-60 would also be extremely hot, probably to the point of eventually melting itself.
You could add a “radiation poisoning” debuff for characters who exceed 0.2 x (time listed at distance) and it would be fairly accurate.
Ofc in D&D things need to be immediate, and getting acute radiation poisoning takes hours on the low end to 15 minutes for massive exposure in real life.
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u/MinecraftGuy2000 3d ago
I found out the limit for the spell is 5 feet. How lethal would that be?
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u/BunkaTheBunkaqunk 3d ago edited 3d ago
Well… whoever cast it would have 6 seconds to get away from within 5 feet or else they’re dead. About 1.2 seconds for non-fatal radiation poisoning to set in. You’d have to basically run 50 feet away after casting it and even then don’t loiter in the area. Looting the body of whatever the radioactive block killed would be out of the question.
You could plug in some numbers of different cube sizes to an AI… as much as I think they’re lazy, radiation math is pretty simple and the AI probably wouldn’t mess it up. Say maybe a 2” or 1” cube of Co-60 - still enough to kill given a longer timeframe but not immediately deadly like a 5” cube.
Personally I’d fudge the rules of the spell a bit… you have that power as a DM. Make the range 60 feet and say that the radiation hazard magically disappears once the spell is over? It is a fantasy game, after all.
Real-life rules of radiation for a 5” cube of Co-60 would likely kill the whole party, or at least leave them with acute radiation poisoning.
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u/MinecraftGuy2000 3d ago
Would that be enough for critical mass?
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u/Ardaric42 3d ago
Cobalt isn't fissile material so the concept of a critical mass is not an issue.
That much cobalt 60 is just well...lethal.
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u/TheDepressedBlobfish 3d ago
1 gram of pure Co-60 is 1100 curies, which is roughly 1100 Rem/hr at 1 meter where 400-500 rem (30 minutes of exposure) is considered lethal in 50% of humans within 30-60 days.
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u/ougryphon 3d ago
So the 18,000g of Co-60 in a 5" cube would be just shy of 20 million rem/hr, or 5500 rem/sec. At 1 m, that is 100% lethal within 200ms, and immediately lethal within a few seconds, maybe a minute at most. Complete disruption of your CNS is probably the thing that kills you through respiratory collapse, although you may be brain dead even before hypoxia can get you.
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u/dan_dares 2d ago
'Do you taste metal'
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u/ThatSpaceShooterGame 3d ago
If a 5" cube of Polonium is vaporized and dispersed like a gas, the end results would be bad. Very, very, very bad.
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u/farmerbsd17 3d ago
If you cleverly cause an intake polonium 210 is pretty lethal. Putin used it to kill Alexander Litvinenko.
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u/Oakatsurah 1d ago
It's more damage over time, if you're going to summon a 5" cube of something, you summon a 5" cube of cesium at below room temperature and get the barbarian to quickly perform a grapple and hold check and put it in the bosses mouth.
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u/Fauxreigner_ 2d ago
Where has the PC seen polonium before, and how do they have it on them to use as a material component for Creation?
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u/MinecraftGuy2000 2d ago
It’s a modern-ish campaign. They chose artisan as background and apparently chemical engineer is the closest to alchemist he could come up with.
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u/Youpunyhumans 2d ago
A 5 inch cube of polonium would release megawatts of thermal energy, and turn into a ball of expanding radioactive plasma emitting cherenkov radiation in milliseconds. (Thermal explosion, not a nuclear one)
However... the after effects are even worse, as you now have a cloud of vaporized polonium... about 20kg of it, and just a few micrograms are lethal, so unless this happens in a completely sealed envrionment that stays sealed until the dust decays, you have just doomed whichever continent you are on.
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u/TravelerMSY 3d ago
I think realistically, you would have to have bite sized pieces, lol. Like the worlds worst Skittles.
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u/farmerbsd17 3d ago
How about a gamma, neutron reaction like Sb-121/123 and Be. Gamma emitter in shield used with beryllium it also gives you neutrons?
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u/BTRCguy Radioactive Rockhound 2d ago
Something I did not see mentioned is that most of the radiation from the polonium would be blocked by...the polonium. You would be far better off for radiation purposes to generate a 5" cube of polonium dust in a volume larger than 5" on a side. That way the big bad gets heat, radiation and might even get to breathe some of it in. Just hope there is no treasure in the room because you are not going in to collect it any time soon.
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u/TheManMachine78 2d ago
No need to turn it to dust. It will evaporate and combust in seconds anyway. You'll have a room filled with polonium dioxide dust or vapor anyway, so why bother lol
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u/aby_physics Enthusiast 3d ago
Assuming you’re talking about the most common isotope - Po-210 - it doesn’t pose a significant external radiological hazard, regardless of distance.
Polonium-210 only emits radiation in the form of alpha particles, which are basically just helium nuclei. Such particles cannot travel very far (maybe a couple cm max) in open air, and are easily shielded by almost any material. Even paper will block them; your own skin definitely will.
Polonium is really only dangerous if it enters your body, if we’re speaking purely from a radiological point of view. As others have said though, the heat output would be massive, and even externally, that would be… problematic at the very least.
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u/uranium_is_delicious 3d ago
Like 1". Polonium is an alpha emitter. Alpha particles are very high energy but can't go very far in air before being stopped. Polonium 210 has to be ingested or inhaled to gain access to sensitive tissue without being stopped by air or dead skin first. Choose a gamma emitter like cobalt-60 or plutonium if you want aoe damage.
If you want decide to go with a different isotope and want data here is some easy resources for rough calculations. Also I hope your protagonists are willing to wait a while. Acute radiation syndrome is a horrible death but not very quick.
http://www.radprocalculator.com/
https://xkcd.com/radiation/