Neutronium Armor: Could it Actually Protect?

[Tisthammerw]

As many of you know, neutronium is a type of matter found in neutron stars. It is incredibly dense (hundreds of millions of metric tons per cubic centimeter) and consists of neutrons sitting right next to each other. In sci-fi (e.g. star trek) neutronium is sometimes used as nearly indestructible armor.

Assuming neutronium armor could be made, how effective would it actually be for protection? IIRC, the force holding neutrons together is far stronger than what holds atoms and molecules together, so on the surface the purported toughness seems reasonable if such armor could be made. But I'd like to be sure. What do you physics experts think?

 

[Hurkyl]

The problem is trying to produce the force that holds the neutronium together, and how to avoid crushing the wearer and everything around him in a 30^* mile radius in the process!

Neutroniu does not stay together of its own volition: it very much wants to explode. It takes the man of an entire sun packed into the (much smaller) volume of a neutron star to keep it together.


*: number picked out of thin air

 

[Astronuc]

As many of you know, neutronium is a type of matter found in neutron stars. It is incredibly dense (hundreds of millions of metric tons per cubic centimeter) and consists of neutrons sitting right next to each other. In sci-fi (e.g. star trek) neutronium is sometimes used as nearly indestructible armor.

Assuming neutronium armor could be made, how effective would it actually be for protection? IIRC, the force holding neutrons together is far stronger than what holds atoms and molecules together, so on the surface the purported toughness seems reasonable if such armor could be made. But I'd like to be sure. What do you physics experts think?

This sounds like Isaac Asimov's Foundation series and the 'nucleics' concept - micronuclear devices.

As Hurkyl pointed out, the conditions required for neutron stars preclude the proximity to humans. The same goes for stars - one cannot develop a fusion power source comparable to a star - the pressures and radiation fluxes are simply too great.

 

[yourdadonapogostick]

As many of you know, neutronium is a type of matter found in neutron stars. It is incredibly dense (hundreds of millions of metric tons per cubic centimeter) and consists of neutrons sitting right next to each other. In sci-fi (e.g. star trek) neutronium is sometimes used as nearly indestructible armor.

Assuming neutronium armor could be made, how effective would it actually be for protection? IIRC, the force holding neutrons together is far stronger than what holds atoms and molecules together, so on the surface the purported toughness seems reasonable if such armor could be made. But I'd like to be sure. What do you physics experts think?

DOOMSDAY MACHINE!
that episode was awesome.

not suitable for like armor to wear on your person.be could for a VERY BIG spaceship, though...although that would make it really difficult to move...

 

[Tisthammerw]

The problem is trying to produce the force that holds the neutronium together, and how to avoid crushing the wearer and everything around him in a 30^* mile radius in the process!

Neutroniu does not stay together of its own volition: it very much wants to explode. It takes the man of an entire sun packed into the (much smaller) volume of a neutron star to keep it together.

Interesting, but then what overcomes the strong force for neutronium to naturally explode? I had heard about the alleged instability of neutronium outside the pressures of a neutronium star on the Internet, but I was suspicious because I didn't know what could overcome the strong force that would seem to hold neutronium together.

 

[Tisthammerw]

This sounds like Isaac Asimov's Foundation series and the 'nucleics' concept - micronuclear devices.

As Hurkyl pointed out, the conditions required for neutron stars preclude the proximity to humans. The same goes for stars - one cannot develop a fusion power source comparable to a star - the pressures and radiation fluxes are simply too great.

Perhaps so, but unfortunately that really doesn't answer my question. If such armor could be made...

...how effective would it actually be for protection? IIRC, the force holding neutrons together is far stronger than what holds atoms and molecules together, so on the surface the purported toughness seems reasonable if such armor could be made. But I'd like to be sure. What do you physics experts think?

As I said earlier, I had heard about the alleged instability of neutronium outside the pressures of a neutronium star on the Internet, but I was suspicious because I didn't know what could overcome the strong force that would seem to hold neutronium together. See for instance, http://www.everything2.com/index.pl?node=neutronium I’m not sure which website to trust, though the latter does seem to make the most sense to my limited knowledge of physics.

 

[Hurkyl]

Gravitational confinement.

Think about this: what force is stopping the neutron star from collapsing into a black hole?

 

[Tisthammerw]

Gravitational confinement.

Can you be a little more specific? Neutronium is very dense and thus has more gravity per cubic centimeter than normal matter. But how exactly would this overcome the strong nuclear force binding it together?

Think about this: what force is stopping the neutron star from collapsing into a black hole?

To be honest, I don't know. All I remember is that given a radius r there must be certain amount of matter (often an enormous amount) needed within that radius for it to become a black hole. So, my best guess for that answer is that there is not enough matter for the star to collapse into a black hole.

 

[CBJammin103]

Basically what they're trying to say (I think) is that in a neutron star, the particles are held together out of the sheer incredible gravitational force that holds any celestial body together. Because of the opposite force the particles exert, the star does not collapse into a black hole.

However, in a smaller "armor-like" usage, there would be no massive graviational force to hold the particles together. There would have to be some other substitute force to do this, which would render any kind of armor basically pointless.

 

[Tisthammerw]

Basically what they're trying to say (I think) is that in a neutron star, the particles are held together out of the sheer incredible gravitational force that holds any celestial body together. Because of the opposite force the particles exert, the star does not collapse into a black hole.

However, in a smaller "armor-like" usage, there would be no massive gravitational force to hold the particles together. There would have to be some other substitute force to do this, which would render any kind of armor basically pointless.

Except that the substitute force would (presumably) be the strong nuclear force--one that does not require a neutron star. In atoms, the strong nuclear force is what holds the nucleus of protons and neutrons together. The idea is that neutronium--albeit very dense--would be held together by the strong nuclear force as opposed to the relatively wimpy atomic bonds. If so, then it seems it could theoretically be used as nearly indestructible armor (as in Star Trek episodes).

If neutronium were to "explode" or at least be unstable outside a neutron star it seems that there would have to be something countering the strong nuclear force that would ordinarily hold neutrons together. My question: what is it?

In some websites such as http://www.everything2.com/index.pl?node_id=1185582 seem to say that neutronium could theoretically act as armor, whereas some say neutronium would be unstable outside of a neutron star. I'm not sure which website to trust, so I came here.

 

[Chronos]

Hurkyl was hinting at the 'Pauli exclusion principle', which is what prevents a neutron star from further collapsing to form a black hole. If you attempted to ferry off with 'neutronium' you mined from a neutron star, it would decompress like a fish yanked from 10,000 feet, only worse... much worse.

 

[Haelfix]

For that matter getting anywhere near a neutron star would be a pretty bad idea. EG how best to implode a human being in 1 short step.

 

[Nereid]

Now, how quickly would a human, somehow 'instantly' transported to a spot some, say, 1 km above the surface of an NS:
a ) be ripped to atoms/molecules, by the tidal force or the magnetic field?
b ) 'fall' to the surface of the NS (how fast would they be going when they hit, assuming the NS has no 'atmosphere')?
c ) become smeared as a monolayer (atoms? neutrons??) over the surface of the NS?

 

[russ_watters]

Except that the substitute force would (presumably) be the strong nuclear force--one that does not require a neutron star. In atoms, the strong nuclear force is what holds the nucleus of protons and neutrons together. The idea is that neutronium--albeit very dense--would be held together by the strong nuclear force as opposed to the relatively wimpy atomic bonds.

You're missing the point (which is ok, because no one has said it yet) - the strong nuclear force does not apply here. The force that keeps electrons orbiting atoms and atoms from collapsing into neutronium is electromagnetism and that force doesn't just vanish when the star collapses. Its still there, trying to separate the electrons from the neutrons, but gravity is what prevents that. Free neutrons are not stable particles.

If a ball of neutrons were a stable configuration of sub-atomic particles, every nuclear reactor would create one, because they are chock-full of free neutrons, floating around. They'd collect piles of them on the bottom of the reactor.

Caveat: this isn't my area of expertise, so if I got this wrong, someone please correct me.

 

[Art]

Neutronium does not stay together of its own volition: it very much wants to explode. It takes the man of an entire sun packed into the (much smaller) volume of a neutron star to keep it together.

Although it takes intense gravitation to create neutronium, once made would it be necessarily unstable if removed from the environment that created it? However with regard to the op, the main problem with making armor from neutronium is that as far as I know neutronium in a neutron star is believed to be a liquid?

 

[Art]

You're missing the point (which is ok, because no one has said it yet) - the strong nuclear force does not apply here. The force that keeps electrons orbiting atoms and atoms from collapsing into neutronium is electromagnetism and that force doesn't just vanish when the star collapses. Its still there, trying to separate the electrons from the neutrons, but gravity is what prevents that. Free neutrons are not stable particles.

If a ball of neutrons were a stable configuration of sub-atomic particles, every nuclear reactor would create one, because they are chock-full of free neutrons, floating around. They'd collect piles of them on the bottom of the reactor.

Caveat: this isn't my area of expertise, so if I got this wrong, someone please correct me.

The neutron (plus a neutrino) is created when a proton and an electron are combined together. The original electron and proton would no longer exist to seek separation.

 

[Hurkyl]

Although it takes intense gravitation to create neutronium, once made would it be necessarily unstable if removed from the environment that created it?

I confess that I cannot prove that, once removed from the neutron star, that some other mechanism will manifest that will provide a confining force equal to that of the gravitation of the neutron star.

However, I see absolutely no reason to suspect such a force will manifest. Do you?

 

[Astronuc]

It is incredibly dense (hundreds of millions of metric tons per cubic centimeter) . . .

Assuming neutronium armor could be made, how effective would it actually be for protection?

If it could be made, it would be an effective armor. The mass density (millions of metric tons per cubic millimeter) would be sufficient to effectively absorb any project impacting it.

On the other hand, it would probably weigh a heck of a lot (millions of metric tons) which means it would take an enormous amount of energy to move anywhere - even just down the street. On the earth, it would probably collapse upon itself and crush whomever was inside, so as an armor it would seem counter-productive - not to mention all those neutrons decaying into protons and beta particles, which would irradiate the occupants of the armor.

If a ball of neutrons were a stable configuration of sub-atomic particles, every nuclear reactor would create one, because they are chock-full of free neutrons, floating around. They'd collect piles of them on the bottom of the reactor.

Neutrons don't accumulate in a reactor, which has normal atomic densities. Neutrons scatter and are absorbed by the fuel, coolant/moderator and structural materials. There are many more atoms (nuclei) than neutrons. A neutron flux in a power reactor is on the order of 10¹⁴ n/cm²-s, while the atomic density is on the order of 10²² n/cc.

 

[Art]

I confess that I cannot prove that, once removed from the neutron star, that some other mechanism will manifest that will provide a confining force equal to that of the gravitation of the neutron star.

However, I see absolutely no reason to suspect such a force will manifest. Do you?

Ignoring your sarcasm, why would a confining force be necessary? What is the force that would be trying to push the neutrally charged neutrons apart which needs to be overcome? When industrial diamonds are created using tremendous pressure they don't suddenly revert to their original form when the pressure is removed.

Edit: From Wikipedia

It is also unknown how neutron star material would behave if the pressures on the star were suddenly reduced.

Seems perhaps it is not quite so obvious that neutronium would need a confining force.

 

[Hurkyl]

What is the force that would be trying to push the neutrally charged neutrons apart which needs to be overcome?

It comes from the Pauli pressure. (Or degeneracy pressure)


In an ordinary solid or liquid, the electromagnetic force will tend to pull nearby molecules together (unless they're too close, in which case they'll be repelled). Without a sufficient force to contain the molecules, the substance would evaporate into a gas simply through the natural motion of the molecules within the substance.


Because the neutrons of neutronium are packed so tightly, there is an enormous variance in their momentum, by the HUP. Without any sort of force to contain the neutrons, they'll simply go on their merry way, much like the particles of a gas.

 

[Tisthammerw]

You're missing the point (which is ok, because no one has said it yet) - the strong nuclear force does not apply here.

Why not?

The force that keeps electrons orbiting atoms and atoms from collapsing into neutronium is electromagnetism and that force doesn't just vanish when the star collapses. Its still there, trying to separate the electrons from the neutrons, but gravity is what prevents that.

Ah, so it’s the electrons mixed into it that makes it unstable. I can understand that. A similar thing happens to elements with high atomic numbers. The positive charge of all those protons "add up" and make the nucleus unstable.

Okay, but what if "pure" neutronium were extracted instead? That is, a big glop of neutrons sitting right next to each other side by side? Wouldn't the strong nuclear force hold them together? If not, why not?

 

[Tisthammerw]

If it could be made, it would be an effective armor. The mass density (millions of metric tons per cubic millimeter) would be sufficient to effectively absorb any project impacting it.

On the other hand, it would probably weigh a heck of a lot (millions of metric tons) which means it would take an enormous amount of energy to move anywhere - even just down the street.

Agreed, but I was considering something more like armor for a starship or starbase. What about a coating of neutronium a few angstroms thick (supposedly being held together by the strong nuclear force)? It would certainly push its weight into more reasonable limits, but (kilogram for kilogram) would it be worth it? Would it really do a better job than conventional armor of the same mass? Neutronium would seem to have the benefit of the strong nuclear force, but I don’t know.

On the earth, it would probably collapse upon itself and crush whomever was inside, so as an armor it would seem counter-productive - not to mention all those neutrons decaying into protons and beta particles, which would irradiate the occupants of the armor.

So neutrons spontaneously decay into protons and beta particles? If so, why do they not do so in the nucleus of atoms (in stable elements, e.g. Titanium)?

 

[russ_watters]

Why not?

Covered in the rest of the post...

Ah, so it’s the electrons mixed into it that makes it unstable. I can understand that. A similar thing happens to elements with high atomic numbers. The positive charge of all those protons "add up" and make the nucleus unstable.

Pretty much, yep.

Okay, but what if "pure" neutronium were extracted instead? That is, a big glop of neutrons sitting right next to each other side by side? Wouldn't the strong nuclear force hold them together? If not, why not?

No. The strong force just doesn't act in that way. It doesn't exist for free neutrons. Neutrons are unstable and have about a 10 minute half life. They would simply decay.

I hate to sound like a broken record, but this is kinda redundant and there isn't really anything else to say besides "it just doesn't work that way". 1 + 1 does not equal 3. Why? It just doesn't.

Maybe it would be helpful if we turned this around: what basis do you have for believing the strong force would hold a free neutron together?

So neutrons spontaneously decay into protons and beta particles? If so, why do they not do so in the nucleus of atoms.

Because inside atoms, the strong nuclear force does exist and holds them together.

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html

Along with protons, neutrons make up the nucleus, held together by the strong force. The neutron is a baryon and is considered to be composed of two down quarks and one up quark.

A free neutron will decay with a half-life of about 10.3 minutes but it is stable if combined into a nucleus.

The neutron (plus a neutrino) is created when a proton and an electron are combined together. The original electron and proton would no longer exist to seek separation.

Neutrons decay into a proton and an electron.

 

[Chronos]

A neutron in the nucleus of an atom is prevented from decaying [in most cases] by the nuclear strong force. Free neutrons [i.e., not captured by an atom] are only constrained by the nuclear weak force. The quarks comprising the neutron are not rigidly bound to each other as they are when subject to the nuclear strong force and will decay [half life ~10 minutes] into the lighter and more stable proton by radiating out an electron and antineutrino. A neutron star is the exception to this general rule... we would otherwise be calling them proton stars! The enormous gravitational pressure basically makes the whole thing behave like a gigantic atomic nucleus. As Hurkyl noted, unless there are new physics waiting to be found [which is always a possibility] neutronium would not be stable once released from the crushing gravitational field. That aside, there are serious logistical issues... like what kind of 'scoop' would you use to harvest your neutronium? Any material composed of atoms would disintegrate before it reached the surface of a neutron star.

 

[Art]

It comes from the Pauli pressure. (Or degeneracy pressure)


In an ordinary solid or liquid, the electromagnetic force will tend to pull nearby molecules together (unless they're too close, in which case they'll be repelled). Without a sufficient force to contain the molecules, the substance would evaporate into a gas simply through the natural motion of the molecules within the substance.


Because the neutrons of neutronium are packed so tightly, there is an enormous variance in their momentum, by the HUP. Without any sort of force to contain the neutrons, they'll simply go on their merry way, much like the particles of a gas.

Doesn't the Pauli exclusion principle simply prevent 2 neutrons occupying the same place thus preventing the neutronium collapsing further and becoming a black hole? If there is a repulsive force causing an explosive like expansion where is this force coming from as I thought Bosons were not involved in the Pauli effect?
Given that without the electromagnetic force, neutronium outside of a neutron stars gravitation would be subject to evaporation would it actually take the same amount of force as supplied by the neutron star's gravitation to prevent this evaporation?

 

[Tisthammerw]

No. The strong force just doesn't act in that way. It doesn't exist for free neutrons. Neutrons are unstable and have about a 10 minute half life. They would simply decay.

Fine, but I wasn't talking about individual neutrons flying around. What if we stack neutrons side by side right next to each other? Wouldn't the strong nuclear force hold them together? Or does the strong nuclear force only apply to neutron-proton interaction and not neutron-neutron?

 

[Janus]

Why not?




Ah, so it’s the electrons mixed into it that makes it unstable. I can understand that. A similar thing happens to elements with high atomic numbers. The positive charge of all those protons "add up" and make the nucleus unstable.

Ah, but nuclei can be unstable from having to many neutrons also. Example: Carbon 12, with 6 neutrons is stable while carbon 14, with 8 is not and undergoes radioactive decay. Another is Lead 214, which is a member of the uranium series. It decays in a series with both Alpha and Beta decays until it reaches lead 206 which is stable. In fact, at points when it decays it actually goes up in atomic number and gains an proton (As when the series decays from Lead 214, atomic number 82 to bismuth 214, atomic number 83)

It takes both protons and neutrons in specifc ratios to each other to make a nucleus stable. Pure neutronium is a sample too small for gravitational binding will decay. l

 

[Tisthammerw]

Ah, but nuclei can be unstable from having to many neutrons also. Example: Carbon 12, with 6 neutrons is stable while carbon 14, with 8 is not and undergoes radioactive decay. Another is Lead 214, which is a member of the uranium series. It decays in a series with both Alpha and Beta decays until it reaches lead 206 which is stable. In fact, at points when it decays it actually goes up in atomic number and gains an proton (As when the series decays from Lead 214, atomic number 82 to bismuth 214, atomic number 83)

It takes both protons and neutrons in specifc ratios to each other to make a nucleus stable. Pure neutronium is a sample too small for gravitational binding will decay.

Interesting, but then what are the "rules" for the stability of a nucleus and the usefulness of the strong nuclear force in binding things together?

 

[Hurkyl]

If there is a repulsive force causing an explosive like expansion where is this force coming from as I thought Bosons were not involved in the Pauli effect?

You don't need a repulsive force to cause an explosive-like expansion. As I suggested, think about how a gas works: pressure is generated simply because the individual molecules are moving. And in the case of neutronium, the HUP will guarantee that the particles are moving quite a lot, which gives rise to a pressure.

 

[Chronos]

The gravitational field of a neutron star 'freezes' the quarks that make up the neutrons... need some math to prove that? This is rapidly becoming a tiresome argument that is pointless.

 

[Danger]

Now, how quickly would a human, somehow 'instantly' transported to a spot some, say, 1 km above the surface of an NS:
a ) be ripped to atoms/molecules, by the tidal force or the magnetic field?
b ) 'fall' to the surface of the NS (how fast would they be going when they hit, assuming the NS has no 'atmosphere')?
c ) become smeared as a monolayer (atoms? neutrons??) over the surface of the NS?

Hi, Nereid;
Nice to see you again. I guess we're not hanging out in the same places much.
a) almost instantly by tidal forces; the magnetics wouldn't matter
b) from 1km altitude, somewhat short of light speed
c) within picoseconds of impact (and it would be in the form of neutrons)
**SPOILER ALERT** regarding Larry Niven's novel 'Protector'... One of the scenarios therein deals with a fellow in an unarmed spaceship being pursued by another ship bent upon his destruction. For reasons of no matter here, he has a high-power rifle on board (30-06 or similar). With the villian closing rapidly, he gets a brainstorm and steers for a nearby neutron star. He puts on his suit, climbs out on the hull with the rifle, and aims at his foe. At the appropriate time, he pulls the trigger and climbs back inside. The villian laughs his ass off at the futility of such a gesture and rapidly closes to weapons range... just in time to get fried into oblivion by the blast of gamma coming up as a consequence of a 180-grain chunk of lead impacting the neutron star at 95% of light speed.

 

[Art]

You don't need a repulsive force to cause an explosive-like expansion. As I suggested, think about how a gas works: pressure is generated simply because the individual molecules are moving. And in the case of neutronium, the HUP will guarantee that the particles are moving quite a lot, which gives rise to a pressure.

I am not disagreeing with you in regard to the neutronium changing from a liquid to a gaseous state. My question is in relation to your original contention which was that it would take the equivalent force of the gravitational field of a neutron star to contain the neutronium. Do you still contend this and if so why? Presumably as with other gasses the energy state (and so the pressure) of the neutrons would depend on the temperature. At 0 K what pressure would the neutronium gas exert?

 

[Hurkyl]

Do you still contend this and if so why?

Yes.

Neutronium's pauli pressure + Neutron star's gravitational pull = 0

And if we had

Neutronium's pauli pressure + some other containment method = 0

then we can solve and get

Neutron star's gravitational pull = some other containment method

At 0 K what pressure would the neutronium gas exert?

By the HUP, neutronium can't get anywhere near 0K, since a group of tightly packed neutrons necessarily exhibits a high variance in momenta.

 

[Art]

Yes.

Neutronium's pauli pressure + Neutron star's gravitational pull = 0

And if we had

Neutronium's pauli pressure + some other containment method = 0

then we can solve and get

Neutron star's gravitational pull = some other containment method

you are assuming they are in a state of delicate balance. To use an analogy: the Earths gravity keeps us rooted to the ground but if it were to diminish even quite substantially, we wouldn't just float off into space. We would still be held to the ground but with a lesser force. It seems probable that as neutron stars vary in size with a resulting variance in gravity that neutronium remains neutronium across a wide spectra. The question is, is there a way of actually calculating the point at which the containment force is no longer strong enough to prevent it's changing form?

 

[Hurkyl]

To use an analogy: the Earths gravity keeps us rooted to the ground but if it were to diminish even quite substantially, we wouldn't just float off into space. We would still be held to the ground but with a lesser force.

While we would remain rooted to the ground, the Earth would lose some of its atmosphere. Why do we lose one thing, but not the other?

Again, it comes back to the motion. Particles in the atmosphere are moving very fast. We are not moving very fast.

Of course, if Earth's gravity were to be sufficiently diminished, we would float off as well.

 

[Entropy]

within picoseconds of impact (and it would be in the form of neutrons)

Actually, the forces at the very surface of the neutron star are not strong enough to insue neutron degradation. The outer most surface of a neutron star is acutally composed of various atomic nuclei, mostly iron isotopes. Then as you barrow deeper neutrons will start to break free and form a neutron superfluid but still have protons and electrons mixed in with it. Then as you get even deeper it will eventually become entirely 100% neutrons. As for the core, it may just continue to be neutrons as well, but it might be that their is further degradation of neutrons into a type of quark matter.

 

[Astronuc]

The gravitational field of a neutron star 'freezes' the quarks that make up the neutrons... need some math to prove that? This is rapidly becoming a tiresome argument that is pointless.

If you mean the discussion of neutronium, yes, I agree. If neutronium could be 'made' into armor, which it can't for the various reasons mentioned, it would make great armor. I am fairly certain that the application of neutronium as armor falls into the realm of 'science fiction, not science and technology.

I would prefer to discuss the structure of neutron stars - which is pretty interesting because we cannot see into a neutron star, but rather we must make an 'educated' guess (or assessment) based upon our understanding of hadrons/baryons, quarks and the properties of matter as we know them.

Perhaps it is worthwhile to pursue further discussion of neutron stars in that thread.

I need to get up to speed on neutron stars - particularly the understanding of the internal structure.

 

[Danger]

Actually, the forces at the very surface of the neutron star are not strong enough to insue neutron degradation... ...it may just continue to be neutrons as well, but it might be that their is further degradation of neutrons into a type of quark matter.

Thanks for the correction, Entropy. It's been a very, very long time since I've had anything to do with the subject, and I'd forgotten about the internal structure variations. For some reason, I was remembering it as just a solid mass of neutrons, along with 'fluid' neutronium. (I think it's because the concept of free protons and electrons continuing to survive in that environment is so counter-intuitive to a non-scientist.) And now that you've mentioned it, the term 'quark soup' in reference to the core comes back to me, but I can't remember who coined it.
Sorry for the mis-lead, Nereid.

 

[Antiphon]

The outer most surface of a neutron star is acutally composed of various atomic nuclei, mostly iron isotopes. Then as you barrow deeper neutrons will start to break free and form a neutron superfluid but still have protons and electrons mixed in with it.

What a shame. I imagined the smooth black surface of solid neutrons
when in fact it's a dirty crusty junk-heap.

The job of a good armour is to absorb or deflect kinetic energy.
I'm not sure neutronium would be good at this even if stable and
thin enough to be wearable. But it would be water-clear in almost
any thickness! Now that would be cool to see.

 

[Chronos]

It takes immense force to pack neutrons as tightly as they are in a neutron star, as Hurkyl correctly noted. That is not in doubt. But indeed, the pure 'neutronium' layer lies beneath the mostly iron nuclei surface of a classical neutron star, as Entropy correctly noted. Not that we are likely to collect, but I would bet if you drug a scoopful of any of this stuff far away its gravity bucket, it would change to something else - and probably with some violence.

 

[LURCH]

I have been following this discuccion and found it more interesting than I expected. The main missunderstanding seems to be in relation to the strong nuclear force. The assumption was that the strong nuclear force would hold together any nucleons that manage to get so close to one another as to be within its very short effective range. Apparently, this is an incorrect assumption regarding neutrons. This leads to an obvious question, is there a causal link between charge and the strong nuclear force? I seem to recall hearing that (somewhat) recent developments in mathematics have revealed a connection between these two forces, with the weak nuclear force having already been unified to electromagnetic force.

I have also heard of the production of "positronium", and I thought I read somewhere that an "anti helium" atom had been produced, which would prove that the strong nuclear force works for negatively charged particles (anti protons), just as it does for protons.

Am I correct in assuming that the absence of strong nuclear force between neutral particles provides physical evidence of the unity between the strong nuclear force and the "electro-weak" force?

 

[Antiphon]

Not that we are likely to collect, but I would bet if you drug a scoopful of any of this stuff far away its gravity bucket, it would change to something else - and probably with some violence.

This must be true, otherwise there would be chunks of it floating around
from supernovas. The average meteorite is bad enough. A hunk of that
going 25k MPH could really ruin your day- and your planet.

 

[Astronuc]

It takes immense force to pack neutrons as tightly as they are in a neutron star, as Hurkyl correctly noted. That is not in doubt. But indeed, the pure 'neutronium' layer lies beneath the mostly iron nuclei surface of a classical neutron star, as Entropy correctly noted. Not that we are likely to collect, but I would bet if you drug a scoopful of any of this stuff far away its gravity bucket, it would change to something else - and probably with some violence.

Assuming one could get a collection device near the surface of a neutron star (remember temperatures are several millions of degrees K), it would become part of the neutron star. But then, consider the distances involved, and we don't have to worry about this hypothetical anytime soon.

I have also heard of the production of "positronium", and I thought I read somewhere that an "anti helium" atom had been produced, which would prove that the strong nuclear force works for negatively charged particles (anti protons), just as it does for protons.

As for positronium, it is a metastable state of a positron and electron, in which positron in free space quickly interacts (via Coulomb force) with an electron, and the pair will for a 'very short time' (10^-10 s) form a bound state. This state is similar to a hydrogen atom with the proton replaced by a positron. Upon annihilation, most commonly, two photons are produced. However, a positron and electron annihilation can sometimes produce three photons upon decay.

See -

Postronium

Positronium puzzle is solved

The Search for Positronium
I am not aware of any anti-He being produced, but I believe there has been some attempts (perhaps some successful) at forming anti-hydrogen. It's difficult given that one must bring a positron and anti-proton to essentially rest. It is one thing to store particles in a storage ring, it is quite another matter [unintentional pun] to bring anti-particles to rest in an environment consisting of normal matter.

The strong nuclear force should work for anti-nucleons, in the same way it works for 'normal' nucleons.

IIRC, the strong nuclear force does not hold two neutrons together, nor is it sufficient to overcome the Coulomb repulsion and keep two protons together - there is a requirement of at least one neutron for one of more protons (e.g. He³).

 

[LURCH]

Whoa, thanks for the correction, Astronuc! Somehow I got the term "positronium" mixed up with "antihydrogen". Don't know how I managed That .

I was trying to talk about the http://info.web.cern.ch/Press/PressReleases/Releases2002/PR09.02Eantihydrogen.html about the production of an anti-helium isotope.

So, the strong nuclear force will bind protons together, and antiprotons as well, but not neutrons. This would seem to imply a direct relationship between strong nuclear force and EM.

At any rate, the inability of strong nuclear force to bind neutrons together is the crucial bit of information needed in evaluating the feasibility of the type of armor alluded to in the original post. I'll also add that, if such armor did exist, I do not think it would collapse under its own weight. It would indeed be incredibly heavy, but it would also be incredibly strong; too strong to collapse. Instead, I think it would most likely sink straight through the crust and mantle of the Earth like a rock falling through air, until it reached the core, when it would sink more like a rock through water.

 

[Mk]

I think it would most likely sink straight through the crust and mantle of the Earth like a rock falling through air, until it reached the core, when it would sink more like a rock through water.

But then it would fly through the core to the center of the Earth, and out the other side from all the momentum it gained.

And up and down and up and down and up and down... That would mess up the environment considerably. The neutronium would cut through a person like a knife through hot butter! OUch! That'll hurt in the morning.

 

[LURCH]

Follow-on question: in theory, can there be variations in density of a neutron star at different depths (not counting the candy coating, I'm just talking about the chewey interior). Can neutronium come in different densities? My geuss would be "no", I would imagine the inside of a neutron star to be about the most homogenous thing in the universe, but it's very hard to grasp that it's no denser at the core than it is near the surface, or that a neutron star that is just above the Chandrasekhar limit is no more dense than one that's just a few metric tons short of collapsing into a BH.

 

[Chronos]

That depends on the equation of state you use to describe the interior of a neutron star... which is a very good question that does not have a very good answer to date.

 

[Astronuc]

That depends on the equation of state you use to describe the interior of a neutron star... which is a very good question that does not have a very good answer to date.

I was wondering about the constitutive model (or equations of state(s)) of a neutron star. I suspect it is beyond anything with which we are familiar. How would one work with a substance that is "millions of tons/cc"?


If one takes the diameter of a neutron as 10^-15 m and the diameter of a typical atom as 10^-10 m and assume a density on the order of 1 gm/cc, then a neutron star has a density on the order of (10^-10/10^-15)³ or 10¹⁵ g/cc or 1 billion metric tons/cc, i.e. it's very HEAVY!

 

[SkepticJ]

Everybody has covered why neutronium armor won't work. Perhaps now we can look at what might? This paper: http://nuri.pusan.ac.kr/~clee/ECT/Bowers.pdf

Has an interesting material called a Crystalline Colour Superconductor. It might be stable and very strong.

 

[NEOclassic]

When nature creates a normal neutron somewhere near the axis of rotation of the Milky Way it throws in what behaves like a singlet positronium that is the seed to the conversion of the neutron to a proton - a spinning electron is ejected with much energy leaving the charge only of the remnant positron still within the neutron shell. Occasionally nature fails to insert a singlet positronium and the result is a mule-neutron that is without the ability to decay so that it simply collects together with other mules and gets denser and denser. Dont forget that there are anti-mules with which the mules could annihilate although spins and magnetics might impede any mixing. Cheers, Jim PS. If this model seems unbelievable just call it sci-fi!