# What would a pile of neutrons look like?

**URL:** <https://boards.straightdope.com/t/what-would-a-pile-of-neutrons-look-like/756979>\
**Category:** Factual Questions\
**Created:** [June 9, 2016, 11:53pm UTC](https://boards.straightdope.com/t/what-would-a-pile-of-neutrons-look-like/756979 "2016-06-09T23:53:11Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\
**Post date:** [June 11, 2016, 12:21am UTC](https://boards.straightdope.com/t/what-would-a-pile-of-neutrons-look-like/756979/21 "2016-06-11T00:21:39Z")

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Trapping neutrons in a bottle is a real experimental technique. The speeds you propose happen to be too low, corresponds to a temperate of 0.0000000001 K. A few millikelvin (0.003 K or so) is achievable, which corresponds to speeds around 10 m/s.

Ultracold neutrons (that’s the technical term) trapped in a bottle behave like an ideal gas if their density isn’t too high. This gas is completely invisible.

You propose having around a kilogram of this stuff. Each neutron that decays releases a teeny bit of energy (“pinprick” was used upthread, but that’s too macroscopic an analogy. The average energy of the electron emanating from a neutron decay is in the ballpark of 10[sup]-13[/sup] joules.

But, a kilogram of them all together? The power output would be over a gigawatt, and the entire energy release (mostly done after an hour or so) would be equivalent to a 6 kton-TNT bomb, about a third the strength of the Hiroshima bomb. In just the first second of the reaction an energy equivalent of 7,000 kg of TNT would be released into the vicinity.

(For experts: this is neglecting the energy of the neutrinos, as one should.)

So your kilogram of neutrons would look… warm.

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**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\
**Post date:** [June 11, 2016, 1:20am UTC](https://boards.straightdope.com/t/what-would-a-pile-of-neutrons-look-like/756979/22 "2016-06-11T01:20:51Z")

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> [@Pantastic](#):
>
> Being overly pedantic and snarky about an ancillary detail of a short post answering a physics question on a message board doesn’t make you look as clever as you think it does, especially when you didn’t even attempt to answer the OP’s question yourself. You are technically correct, which according to pedantic bureaucrats is the best kind of correct.
> 
> Please accept my non-apology for answering the OP’s question in simple language and only referring to the bound state that can safely exist on earth, and not mentioning neutron stars since they’re not really relevant to what the OP asked.

What the hell are you talking about? :dubious: That was a serious question. I don’t know anything about neutron decay so if you think I’m being pedantic then you are seeing goblins everywhere you look for them.

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