What does Linear Energy Transfer measure?

• A. The energy per interaction.
• B. The total energy carried by the radiation.
• C. The amount of energy transferred per unit of path length.
• D. The rate at which energy is deposited along the track per unit length.

Answer: (C)

Linear Energy Transfer measures how much energy a particle deposits as it travels through matter for each unit of distance traveled. It is a spatial quantity, not a rate over time, so it describes energy deposited per unit path length along the track. This tells you how densely the energy is deposited and is key to understanding the potential for biological damage.

The energy per interaction would be the energy lost in a single collision, which is not what LET sums over the whole path. The total energy carried by the radiation is the particle’s initial energy, not how much gets deposited along its path. And a rate implies energy per unit time; LET is not about time, it’s about distance, hence the per-length description. Higher LET means more concentrated energy deposition along the track, like alpha particles, while lower LET corresponds to more sparse energy deposition, like gamma rays.