Which term describes the energy deposition along a radiation track per unit length?

• A. Dose Rate
• B. Absorbed Dose
• C. Exposure
• D. LET

Answer: (D)

Energy deposition along a radiation track per unit length is described by linear energy transfer, or LET. It is quantified as dE/dx, showing how much energy a charged particle loses as it travels a small distance through matter. LET tells you how densely the energy is deposited along the path: high-LET radiation (like alpha particles) dumps a lot of energy into a short span, creating dense ionizations and typically more biological damage for the same absorbed dose. Low-LET radiation (such as X-rays or gamma rays) deposits energy more sparsely, with ionizations spread out over a longer path.

This concept is distinct from dose rate (energy deposited per unit mass per unit time) and absorbed dose (energy per unit mass) or exposure (ionization in air). The key here is the per-length energy loss along the particle’s track, which LET precisely captures.