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Particle Detectors

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A particle detector is a device used to detect, track, and/or identify ionizing particles.

These particles may have been produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator.

Particle detectors can measure the particle’s energy, momentum, spin, charge, particle type, in addition to merely registering the presence of the particle.

Cloud Chamber

(Adapted from Wikipedia)

cloud chamber, also known as a Wilson cloud chamber, is a particle detector used for visualizing the passage of ionizing radiation.

A cloud chamber consists of a sealed environment containing a supersaturated vapor of water or alcohol.

An energetic charged particle (for example, an alpha or beta particle) interacts with the gaseous mixture:

it knocks electrons off gas molecules via electrostatic forces during collisions

This results in a trail of ionized gas particles. They act as condensation centers : a mist-like trail of small droplets form if the gas mixture is at the point of condensation.

These droplets are visible as a “cloud” track that persist for several seconds while the droplets fall through the vapor.

These tracks have characteristic shapes. For example, an alpha particle track is thick and straight, while an electron track is wispy and shows more evidence of deflections by collisions.

Cloud chambers played a prominent role in the experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber.

This is a Diffusion Cloud Chamber used for public demonstrations at the Museum of Technology in Berlin. The first part shows the alpha and beta radiation occurring around us all the time, thanks to normal activity in the atmosphere. Then a sample of Radon 220 (half-life 55 sec) is inserted into the chamber and all hell breaks loose as an alpha-decay party ensues!

Source: Derek McKenzie, Physics Footnotes, http://physicsfootnotes.com/radon-cloud-chamber/



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Learning Standards

SAT Subject Test: Physics

Quantum phenomena, such as photons and photoelectric effect
Atomic, such as the Rutherford and Bohr models, atomic energy levels, and atomic spectra
Nuclear and particle physics, such as radioactivity, nuclear reactions, and fundamental particles
Relativity, such as time dilation, length contraction, and mass-energy equivalence

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Electromagnetic radiation can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. Quantum theory relates the two models…. Knowledge of quantum physics enabled the development of semiconductors, computer chips, and lasers, all of which are now essential components of modern imaging, communications, and information technologies.


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