Consider two people that both received an absorbed dose of 10 milligrays (mGy). One person received that dose from alpha particles, the other from gamma rays. Which dose caused the most biological harm?

Consider two people that both received an absorbed dose of 10 milligrays (mGy). One person received that dose from alpha particles, the other from gamma rays. Which dose caused the most biological harm?

• A. Dose from gamma particles
• B. Both doses will cause an equal amount of biological harm
• C. Dose from alpha particles
• D. Dose from beta particles

Answer: (C)

Different radiations deposit energy in tissue in very different ways, which changes how harmful they are for the same amount of energy deposited. Alpha particles are high-LET (they cause dense, clustered ionizations along their short path), which leads to more complex and harder-to-repair DNA damage per unit of energy. Gamma rays are low-LET, producing more sparsely distributed damage that’s easier for cells to repair. To compare biological impact across radiation types, we use dose equivalents, multiplying the absorbed dose by a radiation weighting factor. Alpha radiation has a weighting factor around 20, while gamma rays (and beta particles) have a weighting factor around 1. So 10 mGy from alpha equals roughly 200 mSv, whereas 10 mGy from gamma equals about 10 mSv. The higher dose equivalent from the alpha exposure means it causes more biological harm, even though the absorbed dose is the same.

Different radiations deposit energy in tissue in very different ways, which changes how harmful they are for the same amount of energy deposited. Alpha particles are high-LET (they cause dense, clustered ionizations along their short path), which leads to more complex and harder-to-repair DNA damage per unit of energy. Gamma rays are low-LET, producing more sparsely distributed damage that’s easier for cells to repair.

To compare biological impact across radiation types, we use dose equivalents, multiplying the absorbed dose by a radiation weighting factor. Alpha radiation has a weighting factor around 20, while gamma rays (and beta particles) have a weighting factor around 1. So 10 mGy from alpha equals roughly 200 mSv, whereas 10 mGy from gamma equals about 10 mSv. The higher dose equivalent from the alpha exposure means it causes more biological harm, even though the absorbed dose is the same.