Which of the following radiation types has the highest linear energy transfer (LET)?

• A. 1 Megavolt of Gamma Rays
• B. 1 Megavolt of Beta Particles
• C. 1 Megavolt of X-Rays
• D. 1 Megavolt of Alpha Particles

Answer: (D)

LET is the energy deposited by radiation per unit length of track as it passes through matter. It tells you how densely the radiation ionizes the material. High LET means a very dense, localized ionization along a short path, which tends to cause more damage in a small volume of tissue.

Alpha particles have a large mass and a +2 charge, so they interact strongly with matter and ionize repeatedly in a very short distance. That dense ionization along a short track gives alpha radiation a much higher LET than the other options.

Gamma rays and X-rays are photons; they deposit energy more sparsely as they travel, leading to low LET. Beta particles are fast electrons with more ionizations than photons but still less dense than alphas, so their LET is lower than that of alpha particles.