Accelerating neutrons, production of ultracold neutrons

[emil2]

Hi to all,

I have two questions concerning neutrons.
How is it possible to accelerate neutrons? Since they have no charge, it shouldn't be possible by applying an electric field. I read somewhere that it should work by using a magnetic field. Can somebody explain how that is working? I mean, how would one construct a "neutron accelerator"?

The second question deals with ultracold neutrons. When fast neutrons from a nuclear reaction or similar emerge, one has to slow them down. I read that normally, one sends them through liquid deuterium. Why is deuterium chosen? Are there other materials or processes which can yield ultracold neutrons?

I am just starting with nuclear physics so please bear with me and my dumb questions...

Thanks
Emil

 

[ZapperZ]

Part (if not all) of your questions may already been addressed in this thread:

https://www.physicsforums.com/showthread.php?t=93441

Zz.

 

[emil2]

Thank you ZapperZ,

I learned a lot from the thread you proposed. But one question still remains, the acceleration of neutrons. In the thread it was just said that neutrons that emerge from a nuclear reaction have a certain kinetic energy. Isn't it possible to further increase it? I mean with charged particles you just use an accelerator operating with electric fields. This won't work for neutrons. So how can they be accelerated?

Emil

 

[ZapperZ]

Thank you ZapperZ,
I learned a lot from the thread you proposed. But one question still remains, the acceleration of neutrons. In the thread it was just said that neutrons that emerge from a nuclear reaction have a certain kinetic energy. Isn't it possible to further increase it? I mean with charged particles you just use an accelerator operating with electric fields. This won't work for neutrons. So how can they be accelerated?
Emil

You don't! Unless you have some sources that indicate that this has been done?

Zz.

 

[Steven S]

One doesn't accelerate neutrons instead if you want neutrons of different energies you can make them using a spallation source. Take a proton beam and smack it into a neutron rich target and the reaction will create a ton of neutrons+other crap. Using time of flight methods one can do experiments with neutrons of different energy.

Obviously if one is going to slow down neutrons one needs a material where neutron capture isn't significant. But I'm not entirely sure why deterium is the preferred material. But I'm sure Golub's book on ultra cold neutrons could probably tell you.

 

[ZapperZ]

One doesn't accelerate neutrons instead if you want neutrons of different energies you can make them using a spallation source. Take a proton beam and smack it into a neutron rich target and the reaction will create a ton of neutrons+other crap. Using time of flight methods one can do experiments with neutrons of different energy.
Obviously if one is going to slow down neutrons one needs a material where neutron capture isn't significant. But I'm not entirely sure why deterium is the preferred material. But I'm sure Golub's book on ultra cold neutrons could probably tell you.

One way to slow down something is to make it collide - but not collide with anything. If a particle collide with another particle of roughly the same mass, this is the most effective means of slowing that first particle. If it collides with something significantly more massive, all that will happen is that it changes momentum without changing its KE.

Thus, water (as in a typical fission reactor) and D are the most effective medium to slow down neutrons, because each of these contains particles (H and D) that has almost the same mass as the neutron.

Zz.

 

[Gokul43201]

Also, if I'm not mistaken, deuterium has a much smaller absorption cross-section for neutrons than regular hydrogen - it's easier for H to become D than for D to become T (that's why heavy water is preferred to aquafina).

 

[Tide]

It is theoretically possible to accelerate neutrons. They have a magnetic moment and can be accelerated by a magnetic field with a (very!) strong gradient.

 

[ZapperZ]

It is theoretically possible to accelerate neutrons. They have a magnetic moment and can be accelerated by a magnetic field with a (very!) strong gradient.

But I think if we want to go to that extreme, I can also say that a neutron (or any elementary particle for that matter) can also be accelerated by a stream of photons - and this isn't too far off since laser acceleration scheme has been shown to work in electron accelerators. However, it is accurate to say that we do not do this, and can't do it, to neutrons with the current technology. There are no neutron accelerators. Injectors, yes, but not accelerators.

Zz.