Quality factors for gamma, alpha and fast neutrons are:

• A. 1,20,10
• B. 2,20,10
• C. 1,10,20
• D. 1,20,20

Answer: (A)

Biological damage from radiation is related to how densely energy is deposited in tissue, not just the total energy. To compare different radiations, we use a radiation weighting factor (quality factor) so absorbed dose in Gy becomes an equivalent dose in Sv.

For gamma rays, which are photons with low LET, the quality factor is 1, so the equivalent dose equals the absorbed dose. Alpha particles deposit energy very densely and cause much more damage per unit energy, so they have a high quality factor of 20. Fast neutrons have higher LET than gamma but less than alpha, and a common value used for fast neutrons is 10.

So the standard set is gamma 1, alpha 20, fast neutrons 10. For example, 1 Gy of gamma corresponds to 1 Sv, 1 Gy of alpha corresponds to 20 Sv, and 1 Gy of fast neutrons corresponds to 10 Sv. (Neutron weighting can vary with energy, but 10 is the typical value used for fast neutrons in many practice guidelines.)