Which characteristic of alpha particles contributes to high biological damage per unit path length?

• A. High penetrating power
• B. Low LET
• C. Long range
• D. High LET

Answer: (D)

The main idea is LET, which is how much energy a radiation particle deposits in tissue for each unit of distance traveled. Alpha particles are heavy and carry a +2 charge, so they interact strongly with atoms in their path. This causes a dense trail of ionizations over a very short distance, meaning a lot of energy is dumped into a small volume of tissue. That concentrated energy deposition leads to complex DNA damage, like clustered double-strand breaks, which are harder for cells to repair. Because the energy is released over a short path, the damage per micrometer of tissue is high, making alpha radiation particularly damaging on a per-unit-length basis even though its overall range is short.