Which radiation has the highest LET among common radiations?

• A. X-rays
• B. Gamma rays
• C. Beta particles
• D. Alpha particles

Answer: (D)

LET, or linear energy transfer, is about how densely a radiation deposit’s energy as it travels through matter. The higher the LET, the more ionizations occur in a tight path, causing more damage in a small region. Alpha particles are the highest LET among these common radiations because they are heavy, doubly charged helium nuclei. Their interactions deposit a lot of energy over a very short distance, producing a dense cluster of ionizations along their track. X-rays and gamma rays are photons and interact sparsely, giving them low LET. Beta particles, being lighter charged particles, deposit more energy than photons but less than alpha particles, giving them an intermediate LET. So alpha particles transfer the most energy per unit length, hence the highest LET.