1. For Electromagnetic Radiation (like X-rays or Gamma rays):
* Linear Attenuation Coefficient (μ): This measures how much the intensity of the radiation decreases per unit distance travelled through the substance. It's expressed in units of inverse length (e.g., cm⁻¹).
* Half-Value Layer (HVL): This is the thickness of the substance required to reduce the intensity of the radiation by half. It's related to the linear attenuation coefficient.
* Transmission: This refers to the fraction of the initial radiation that passes through the substance. It can be calculated using the formula: Transmission = exp(-μx), where x is the thickness of the substance.
2. For Particle Radiation (like alpha particles or beta particles):
* Stopping Power: This measures the energy loss per unit distance of the particles as they travel through the gas. It's expressed in units of energy loss per unit distance (e.g., MeV/cm).
* Range: This is the maximum distance a particle can travel through the gas before it loses all its energy. It's related to the stopping power.
* Fluence: This is the number of particles passing through a unit area of the gas. It's expressed in units of particles per unit area (e.g., particles/cm²).
3. For Neutron Radiation:
* Macroscopic Cross Section (Σ): This measures the probability of a neutron interacting with a gas molecule per unit volume. It's expressed in units of inverse length (e.g., cm⁻¹).
* Mean Free Path (λ): This is the average distance a neutron travels before interacting with a gas molecule. It's related to the macroscopic cross section.
Important Notes:
* The specific measures used will depend on the type of radiation, the gas, and the application.
* The attenuation and interaction of radiation with matter are complex phenomena. These measures provide a simplified way to understand the behavior of radiation in gas.
* Instruments like Geiger counters, scintillators, and ionization chambers are used to measure radiation levels and provide information about the amount of radiation passing through a substance.
Let me know if you have any more specific questions about the measures of radiation passing through a gas. I'm here to help!
