Interaction of Charged Particles with Matter
Charged particles (e.g., electrons, protons, alpha particles, heavy ions) interact with matter mainly through electromagnetic forces with the atomic nuclei and electrons of the medium.
- These interactions lead to energy loss, ionization, and excitation.
- Understanding these processes is crucial in medical physics, radiology, radiotherapy, and radiation protection, since biological effects depend on how energy is transferred to tissues.
Stopping Power (Braking Ability)
- Definition: The capacity of matter to slow down charged particles.
- Stopping Power (S): Energy loss per unit path length.
Units: MeV/cm or keV/μm.
Linear Stopping Power
- Quantifies how much energy a particle loses while traveling through a medium per unit distance.
- Important for:
- Radiation shielding design.
- Estimating tissue dose in radiobiology and therapy.
Linear Ionization & Linear Energy Transfer (LET)
- Linear Ionization (N(L)):
- Number of ion pairs created per unit track length.
- Alpha particles → high N(L), because they strongly interact with electrons.
- Linear Energy Transfer (LET):
- Describes the energy transferred to matter per unit distance.
- High LET → greater biological damage (e.g., alpha radiation).
- Low LET → less dense ionization (e.g., beta particles, X-rays).