Physics of a Cloud Chamber: Neutrons, Kinetic Energy, and Ionization

[cragar]

Why can't I have a neutral particle come into a cloud chamber and leave a track? I was reading about cloud chambers and it says when the charged particle comes in it ionizes the vapor in the chamber. But why couldn't a neutron come in and ionize the particles in the chamber with its kinetic energy? Or would the neutron have to be traveling pretty fast. Just for an approximation i set the kinetic energy of a neutron equal to the ionization energy of a hydrogen atom, and the neutron had to be going pretty fast. And also why does the alcohol vapor have to be ionized to form liquid droplets?

 

[Simon Bridge]

For the neutron to ionize the anything kinetically it would have to "collide physically" with the atoms while a charged particle can interact at a distance as it were, electromagnetically. Actually, neutrons interact via their magnetic moment (as well as nuclear).
http://bcs.whfreeman.com/tiplermodernphysics4e/content/cat_020/InteractionParticlesandMatter.pdf [Broken]
(scroll down to the neutron bit.)
This won't affect electrons ... you have to figure out how to get the neutron's kinetic energy into the electron. Remember, these are not like billiard balls.

The alchohol vapor does not have to be ionised to form droplets... but in the saturated condition in the chamber, droplets will form around ions - because of the physics of dew formation. The ions can be in the vapor, but iirc they are usually in the air inside the chamber and the falling vapor picks them out like the opposite of when you huff on a window you've drawn on with your finger. (The oils from your finger prevent droplet formation.)

Droplets also form on dust - so we have to keep the chamber very clean.

http://en.wikipedia.org/wiki/Cloud_chamber#Structure_and_operation

 

[cragar]

thanks for your answer