Nuclear fission quick question

[padraig]

Hi, just unsure about a question I wonder if you can help me with: How do the neutrons released after nuclear fission differ from those absorbed to begin the reaction in the first place. I think this may be asking me about delayed neutrons, but this is more to do with how the neutrons are made rather than any properties/statistics they may have.

Any ideas??

Many thanks

Patrick

[chroot]

A neutron is a neutron; there are no differences from one to the next, other than circumstances like their velocities. The neutrons are not "made," they are simply released from the fissioning nucleus.

- Warren

[padraig]

I know that they are all the same, by 'properties/statistics' I did mean velocities etc. And by 'made' i was just referring to a delayed neutron being called so because it takes time to be emitted DURING the fission process. So then, do you know of any changes in VELOCITY of the neutrons that occur before/after fission?

[chroot]

The neutrons coming out of a fissioning nucleus are usually travelling very, very fast. In fact, nuclear reactors have to use a "moderator" substance to slow the neutrons down so they can interact with other nuclei. Otherwise they'd just fly out of the reactor, hit the containment walls, and be wasted.

- Warren

[padraig]

cheers

Pat

[chroot]

I guess that means I answered your question? Good. :smile: Welcome to pf.

- Warren

[swansont]

And by 'made' i was just referring to a delayed neutron being called so because it takes time to be emitted DURING the fission process.

Delayed neutrons are not produced by or during the fission. They are the result of the de-excitation of fission products undergoing beta decay.

Prompt neutrons carry away ~2 MeV on average, but it's a spectrum - the most probable energy is about 0.7 MeV. Delayed neutrons have somewhat less energy.