Detection of a photon using a gas-based particle detector:
1. Photon Interaction with Gas: Photons, which are particles of light, have no charge. When a photon enters the particle detector and interacts with the gas inside, it doesn't directly produce a charge. However, it transfers energy to the gas atoms or molecules.
2. Ionization of Gas Atoms/Molecules: This energy transfer can ionize the gas atoms or molecules, meaning it knocks out electrons from them. These freed electrons are the start of the detection process. The photon essentially creates free electrons and positively charged ions in the gas.
3. Avalanche Effect in Gas: In the presence of a strong electric field (the accelerating potential), these free electrons gain kinetic energy. As they move rapidly through the gas, they collide with other gas atoms, ionizing them as well thanks to the kinetic energy gained, and they continue their way. This leads to more free electrons, which in turn ionize more atoms. This chain reaction is known as an avalanche effect and results in a large number of electrons and ions within a very short time.
4. Detection of the Electron Pulse: This avalanche of electrons and ions creates a current or a pulse that can be detected. The strength of this pulse is proportional to the energy of the original photon. This allows not only for the detection of the photon but also for the measurement of its energy.
5. Amplification and Measurement: The initial interaction of the photon with the gas, which resulted in just a few freed electrons, is thus amplified into a large, measurable signal. This amplified signal can then be processed and analyzed to provide information about the photon, such as its energy, and depending on the design of the detector, possibly its direction of travel.
In summary, the photon's energy is converted into an electrical signal via a cascade of interactions in the gas, which is then amplified and measured. This is how gas-based particle detectors can detect and analyze photons, which are otherwise elusive due to their lack of charge and mass.
Regarding point 3, when the electron encounter another molecule, it is true that it frees a new electro, but it is lost, itself, inside the molecule. So I cannot see how the chain reaction is achieved
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Author of the notes: Antonio J. Pan-Collantes
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