Neutrons: Can They Be Confined and Manipulated?

[cybernomad]

If not why not?

 

[Pengwuino]

Huh?

... well since air has neutrons... and I've been near many air filled bottles before... i suppose its possible.

 

[Gokul43201]

In theory, I guess it's possible. In practice, it would be pretty hard to do over any extended period of time. Being chargeless, you can not confine them electrostatically. I imagine you might be able to confine them magnetically with truly giant fields.

Come to think of it...a neutron star is just that - bottled neutrons !

 

[DaveC426913]

But could they literally be bottled? Why would an ordinary container not hold them?

 

[tmc]

if you place a giant bottle around a neutron star, you will have bottled neutrons.
Therefore, this is possible.

 

[Gokul43201]

But could they literally be bottled? Why would an ordinary container not hold them?

Made of the right isotope, it might work for a while. But eventually the neutrons will be absorbed by the atoms of the container.

 

[DaveC426913]

if you place a giant bottle around a neutron star, you will have bottled neutrons.
Therefore, this is possible.

Yeah yeah Smartypants. We're not looking for a logical debate about semantics, we're looking for illumination on physics.

Made of the right isotope, it might work for a while. But eventually the neutrons will be absorbed by the atoms of the container.

Would the atoms of the container then be isotopic and radioactive? That being the case, would they eventually emit their neutrons again (OK, after zillions of years)?

So, the net effect is that the neutrons would slowly diffuse right through the solid container by first being absorbed then emitted from the atoms of the container? Is the time that takes estimable?

And doesn't that ultimately mean that, yes, you could have a jar of neutrons, but that it would eventually empty itself?

Do free neutrons acts as a gas (OK, plasma)? Would there be pressure in the jar? Would it exist at room temp.?

So many thoughts. What an intriguing question.

 

[Physics Monkey]

Ultracold neutrons can be bottled partly because it turns out that neutrons can be reflected by the surfaces of many metals. The first serious work on this done by Zeldovitch in 1959 though several people, including Fermi, had apparently thought about it before. Here is a nice review article: Golub, R. Ultracold neutrons: their role in the study of condensed matter. Rev. Mod. Phys. 68, 329-347 (1996).

Also, storage times can be made longer than a hundred seconds which can be pretty long depending on your attitude. One use of these neutron bottles is to measure the neutron lifetime and electric dipole moment. Another good reference by Ramsey is Ramsey, N. Annu. Rev. Nucl. Part. Sci. 40, 1-14 (1990).

 

[Astronuc]

On earth, and in fact, outside of neutron stars, free neutrons do not exist very long - they decay to a proton, electron (beta particle), and electron-associated neutrino. The half-life of a free neutron is approximately 10.3 minutes, and it is conceivable that a small fraction of neutrons would survive for about one hour - approximately 1 in 1000 neutrons would exist for 10 half-lives.

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c3

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c4

Given enough time, free neutrons which do not decay, will find an atom and be absorbed by the nucleus, which usually emits a gamma ray. The atomic mass of the nucleus increases by 1 amu (approximately) and it usually becomes radioactive, if it is not a stable isotope. Most radionuclides decay by beta (electron) emission.

 

[cybernomad]

Question b)

If then it's plausible to bottle neutrons despite the 10.3 minute half life, what would be its physical characteristics? Do you think it might be similar to liquid helium but extremely dense?

 

[Physics Monkey]

As Astronuc said, neutrons decay in free space and the trap doesn't affect this. In fact, as I mentioned, such setups are actually used to measure the lifetime of the neutron so the trap must not affect the lifetime if the data is to be useful. You mentioned liquid Helium, and the interesting thing about these experiments is that the ultracold neutrons are often kept in a ^4 He bath. The neutrons scatter very little with the superfluid Helium, but ^3 He absorbs neutrons readily. This means the superfluid Helium must be extremely pure. Regarding the density, the ultra cold neutrons are extremely dilute, typically something like 1 UCN per cm^3.

I think you have in mind more the situation in the heart of a neutron star.

 

[Astronuc]

⁴He basically doesn't absorb neutrons, making it the most stable nucleus.

A free neutron is a neutron outside of nucleus, and it will simply decay without the interaction of a proton or group of nucleons.

A neutron star, in fact any star, possesses characteristics of particle density, pressure and radiation beyond anything that can be created by man.

Adding to what Physics Monkey mentioned, ³He is such a good neutron absorber that it is used in special experimental systems as a neutron shield, which when depressurized rapidly exposes short nuclear fuel rods to transient neutron fluxes, sometimes with very interesting results.

 

[cybernomad]

I think you have in mind more the situation in the heart of a neutron star.

I'm just a layman and science buff who was wondering since neutrons can exist in free form and having no electric interaction between them and being far smaller (I guess) than say a typical atom; what their physical characteristics would be if say I was to gather a gram of them in a container. My guess before I asked here would be something along the line of liquid helium, having no viscosity, only that it my be extremely dense.

 

[Gokul43201]

Liquid helium is superfluid (devoid of viscosity) only if cooled below a critical temperature of about 2K (the lambda point). But he-4 is bosonic and neutrons are not. It's easier for bosonic particles to exhibit superfluidity than a fermionic gas.

Nevertheless, superfluidity has been seen in fermionic matter as well (see Ketterle's work, for instance), and I'm sure I've come across work that talks about superfluidity (and vortex formation) in neutron stars. I have not, however, come across any mention of superfluidity in ultra-cold neutrons (other than the reference to superfluid He-4 used for storage).

 

[DaveC426913]

OK, let's set aside the talk about superfluid helium for a moment.

What properties might a jar of neutrons have? A gas? Could it exist for any practical duration at room temp.?

 

[Umabel]

And while we're at it, what properties would a jar of electrons have?

 

[Mk]

Could it exist for any practical duration at room temp.?

Well the half-life is ~865 seconds - 15 minutes.

 

[Entropy]

And while we're at it, what properties would a jar of electrons have?

It would just be a container with an electric field that holds electrons in place and stops them from making physical contact with the walls of the jar.

 

[vanesch]

If not why not?

But they can (if they are cold) ! We do it all the time over here in our institute.
My collegues from the cold neutron group have this bottle:
http://www.ill.fr/nfp/npp/Pf2.htm

 

[Astronuc]

OK, let's set aside the talk about superfluid helium for a moment.
What properties might a jar of neutrons have? A gas? Could it exist for any practical duration at room temp.?

I would think that a population of neutrons mixed in with liquid He-4 is simply a solution of neutrons in a liquid. I doubt that the number of neutrons is anywhere near the number of He atoms. My guess would be something like 1 n for about 10¹⁸ He atoms - and I am probably an order of magnitude or two off.

Presumably the diffusion equations applies as it does in the case of thermal neutrons.

According to the link provided by Vanesch - the flux of cold neutrons is something like 10⁴ n/cm²-s, which is about 10 orders of magnitude below that of commercial nuclear reactor at full power.

 

[cybernomad]

But they can (if they are cold) ! We do it all the time over here in our institute.
My collegues from the cold neutron group have this bottle:
http://www.ill.fr/nfp/npp/Pf2.htm

quick questions:

Would neutrons merely bounce off each other having no force between them?

What would the density (grams cm³)of the cold neutrons be under 1 G and 1 atmosphere?

 

[misskitty]

What is the definition of a superfluid?

I would think the neutrons would bounce off each other since there is no repulsion force keeping them separated and since the neutrons have no charge then it would make sense that the electrons would just bounce off of one another.

How cold would the neutrons have to be to keep them from being absorbed into the bottle?

If a proton, neutrons, and electrons come into contact with one another is it possible they would bond together to become an atom? Or is there a temperature this occurs at and is not possible to over come this temperature on Earth?

~Kitty

 

[McQueen]

Can neutrons be bottled?

--------------------------------------------------------------------------------

If not why not?

The answer is , yes , and it is quite easy to do especially if you are anywhjere near a nuclear reactor ! Neutrons seprated from the nucleus have a half life of about 12 mins. a proton and an electron and neutrino are the end result.

 

[misskitty]

How is it that a single neutron decays into a proton, an electron, and a neutrino when the mass of the neutron is the same as that of a proton?

~Kitty

 

[ZapperZ]

How is it that a single neutron decays into a proton, an electron, and a neutrino when the mass of the neutron is the same as that of a proton?
~Kitty

The mass of a neutron is not the same as the mass of a proton.

Zz.

 

[Astronuc]

How is it that a single neutron decays into a proton, an electron, and a neutrino when the mass of the neutron is the same as that of a proton?
~Kitty

Realize that from an atomic standpoint the mass difference between a proton and neutron is small, and both are assigned 1 amu, but that is an approximation.

The rest mass of a proton is 938.272 MeV/c² or 1.6726 × 10^-27 kg, and a neutron's rest mass is 939.573 MeV/c² or 1.6749 × 10^-27 kg.

1.3 MeV is a fair mass difference on the nuclear scale.

 

[cybernomad]

No one has answered this question.

quick questions:
Would neutrons merely bounce off each other having no force between them?
What would the density (grams cm³)of the cold neutrons be under 1 G and 1 atmosphere?

So let’s put it this way. If I has a gram of neutrons near absolute zero in a vacuum bottle what would its physical characteristics be? Now let’s ignore the half life for now and assume the neutrons are not absorbed into the walls of the container. My guess is that it will settle into some sort of ultra dense superfluid.

Anybody?

 

[ZapperZ]

So let’s put it this way. If I has a gram of neutrons near absolute zero in a vacuum bottle what would its physical characteristics be? Now let’s ignore the half life for now and assume the neutrons are not absorbed into the walls of the container. My guess is that it will settle into some sort of ultra dense superfluid.
Anybody?

Honestly, the topic of this thread is not making any sense, and that physics is being discarded for hand-waving arguments. For example:

"My guess is that it will settle into some sort of ultra dense superfluid."

How do you propose this could happen? A neutron is a fermion. What sort of mechanism do you think would allow such a thing to become a boson and form a superfluid?

But I can already anticipate the follow-up question: Wasn't there already some report on fermionic condensate a few months back? Sure, but that requires a MECHANISM to cause the PAIRING of two fermion to form a composite boson (i.e. similar to the formation of cooper pairs in a superconductor). In the fermionic condensate case, the external magnetic field is require as the "glue" for such a formation of pairs. You have mentioned no such glue.

Next door to my building is a facility called the IPNS - Intense Pulsed Neutron Source. They WISH they can contain neutrons for even a brief period of time, believe me. But they can't, and no one can so far.

Zz.

 

[Hooloovoo]

How is it that a single neutron decays into a proton, an electron, and a neutrino when the mass of the neutron is the same as that of a proton?
~Kitty

A neutron is made of 2 down-quarks and 1 up-quark. Charge 0, mass 9.5-20 MeV/c^2 (actual mass is what was said above).

(downs have a charge of -1/3 and a mass of between 4 and 8 MeV/c^2)
(ups have a charge of +2/3 and a mass of between 1.5 and 4 MeV/c^2)

A proton is made of 1 down-quark and 2 up-quarks. Charge +1, mass 7-16 MeV/c^2 (actual mass is whas was said above).

A neutron decays by converting one of its down-quarks into an up-quark.

This happens by emitting a W-boson (a carrier of the Weak force). W-boson has a charge of -1, and a mass of 80.4 GeV/c^2. Very massive!

Then the W-boson itself decays into an electron and an antineutrino.

This whole process is called beta-minus decay. Because a neutron is more massive than a proton, this can happen in isolation. It's losing mass.

There is a similar process call beta-plus decay, in which a proton decays into a neutron and a positron and a neutrino, but it won’t happen in isolation because it requires an increase of mass.

 

[cybernomad]

But I can already anticipate the follow-up question: Wasn't there already some report on fermionic condensate a few months back?

No, you give me far too much credit. I'm a newbie and a layman who's curious about physics and reads up on science but has joined this forum to ask actual scientists in an interactive way.

Thanks for your contribution.