# Can neutrons be bottled?

1. Oct 27, 2005

If not why not?

2. Oct 27, 2005

### Pengwuino

Huh?

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

3. Oct 27, 2005

### Gokul43201

Staff Emeritus
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 !

4. Oct 27, 2005

### DaveC426913

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

5. Oct 27, 2005

### tmc

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

6. Oct 27, 2005

### Gokul43201

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

7. Oct 28, 2005

### DaveC426913

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

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.

8. Oct 28, 2005

### 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).

Last edited: Oct 28, 2005
9. Oct 28, 2005

### Staff: Mentor

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.

10. Oct 28, 2005

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?

11. Oct 28, 2005

### 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.

Last edited: Oct 28, 2005
12. Oct 28, 2005

### Staff: Mentor

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.

Last edited: Oct 28, 2005
13. Oct 28, 2005

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.

14. Oct 29, 2005

### Gokul43201

Staff Emeritus
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).

15. Oct 29, 2005

### 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.?

16. Nov 7, 2005

### Umabel

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

17. Nov 7, 2005

### Mk

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

18. Nov 8, 2005

### Entropy

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.

19. Nov 8, 2005

### vanesch

Staff Emeritus
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

20. Nov 8, 2005

### Staff: Mentor

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.