Positrons in a Cloud Chamber

This is a video showing positrons (and gamma rays) from a Fluorine-18 source made visible via a cloud chamber. The tracks coming directly from the source are (most likely) positrons stopping and then annihilating. Tracks not pointing to the source are either gamma rays scattering electrons (Compton scattering). The final even shows what is possibly a positron annihilating (without first generating a visible track) followed by both photons scattering electrons. A few events (ones with fuzzy cloud tracks) are likely Cosmic rays striking the chamber from above.

Category:

Science & Technology

Tags:

• positron
• antimatter
• particle physics
• cloud chamber
• fluorine
• radioactivity
• angels and demons
• antielectron

[freemanx2x]

Why sometimes it seems that the particle that creates the trail doesn't originate from the radioactive sample? And why the trail only forms when the particle is at a certain distance from the sample?

[MoorePhysics]

@freemanx2x These could be several things: a gamma-ray photon from a positron-electron annihilation scattering an electron from an atom, cosmic rays unrelated to the sample etc.

Cloud chambers are not very good detectors and generally clouds will only form around "slow" moving charged particles because these are more heavily ionizing. If you look carefully some tracks stop before leaving the chamber and are more dense towards the end - this is the particle slowing down and stopping.

[MoorePhysics]

Correct - the Fluorine decays into Oxygen-18, a positron and an electron neutrino and energy is released. This is the end of the decay chain since O-18 is stable and exists in nature where its ratio to O-16 (the most abundant isotope) in ice cores can be used to measure the mean global temperature when the ice was laid down.

[b0gdanB]

this is so awesome

[elchippe]

Two particles annihilating each other and you can see explosion with the naked eye, very big energy is release in the explosion because the electron and positron have almost zero size.

[LuxuryBarrage]

@ghostalin Total win.

[utkanos]

That clouds apears becose the mowement of the particle or becouse of the energy emited when positron colides with electron?

[Mangoose95]

MoorePhysics, could you please tell me the process of this? There are several problem that we're facing, like the decay energy and the supersaturated solution used inside the vacuum chamber. Need help.

[Mangoose95]

@BotGuides4U

109.77 minutes

[BotGuides4U]

What is the average half-life of F-18?

[ghostalin]

@MoorePhysics Science is SO awesome.