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

In summary, a neutral particle such as a neutron cannot leave a track in a cloud chamber because it does not interact electromagnetically like charged particles do. Instead, it interacts via its magnetic moment and would have to physically collide with atoms to ionize them. Additionally, alcohol vapor does not have to be ionized to form droplets in a cloud chamber, but in the saturated condition, droplets will form around ions due to the physics of dew formation. These ions can come from the vapor or from the air inside the chamber, and droplets can also form on dust, so keeping the chamber clean is important.
  • #1
cragar
2,552
3
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?
 
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  • #2
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
(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
 
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  • #3
thanks for your answer
 

1. What is a cloud chamber and how does it work?

A cloud chamber is a device used in particle physics to detect the presence and track the movement of subatomic particles. It works by creating a supersaturated vapor of alcohol or water vapor within a sealed chamber. When charged particles pass through the chamber, they ionize the vapor, causing droplets to form and create a visible track.

2. What is the role of neutrons in a cloud chamber?

Neutrons are neutral particles found in the nucleus of an atom. In a cloud chamber, they play a critical role in creating the visible tracks. When high-energy neutrons collide with atoms in the chamber, they can knock off electrons and create ionization trails that can be observed.

3. How does kinetic energy affect the tracks in a cloud chamber?

Kinetic energy is the energy an object possesses due to its motion. In a cloud chamber, high-energy particles with more kinetic energy will produce longer and more visible tracks compared to particles with lower kinetic energy. This allows scientists to determine the energy levels of the particles being detected.

4. What is ionization and why is it important in a cloud chamber?

Ionization is the process of adding or removing electrons from an atom, resulting in a charged particle. In a cloud chamber, the ionization of vapor by charged particles allows for the detection and tracking of these particles. This is important because it provides valuable information about the properties and behavior of subatomic particles.

5. How is the data from a cloud chamber used in physics research?

The data collected from a cloud chamber can be used to study the behavior of subatomic particles and their interactions with matter. It can also be used to verify theoretical models and make new discoveries about the fundamental building blocks of the universe. Additionally, cloud chambers are used in educational settings to demonstrate the principles of particle physics and engage students in hands-on learning.

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