1. Who discovered X-rays and in which year?
2. What is the main difference between directly ionizing and indirectly ionizing radiation?
3. Which physical quantity measures the energy deposited per unit length by radiation and what is its typical unit?
What is ionizing radiation?
Ionizing radiation has enough energy to create ion pairs by ejecting electrons from atoms or molecules. It includes electromagnetic types like X-rays and gamma rays, as well as particles such as electrons, protons, alphas, and neutrons.
Name and briefly describe the three main photon interaction mechanisms relevant in medical physics.
The photoelectric effect involves photon absorption where an inner-shell electron is ejected, dominant at low energies with high atomic number materials. Compton scattering is when photons scatter off electrons, transferring part of their energy, important at intermediate energies (~4-25 MeV). Pair production occurs when a photon with energy above 1.022 MeV converts into an electron-positron pair near a nucleus, relevant at energies >10 MeV.
Explain the concept of Linear Energy Transfer (LET) and its significance in radiobiology.
LET is the energy deposited by radiation per unit length traveled in tissue, measured in keV/μm. High LET radiation (e.g., alpha particles) causes dense, localized damage that is often irreparable, leading to higher biological effectiveness, while low LET radiation (e.g., X-rays) results in more spread-out, reparable damage.
Ionizing radiation — definition?
Energy capable of ionizing atoms or molecules.
Activity (A) — formula?
A = λN (decay rate).
Photoelectric effect — energy dependence?
More likely with higher Z and lower energy.
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