What is the weighting factor for protons with energy greater than 2 MeV?

The correct answer for the weighting factor for protons with energy greater than 2 MeV is indeed 5. In radiation protection and dosimetry, the weighting factor (often referred to as the quality factor) is used to account for the different biological effects of various types of ionizing radiation.

Protons, as charged particles, have a greater potential for causing biological damage compared to low-energy photons (such as X-rays and gamma rays), which have a weighting factor of 1. The reasoning behind this increased weighting factor for protons is based on their greater mass and charge, which lead to more ionization events within a given volume of tissue when they interact with it.

As the energy of protons increases above a certain threshold—in this case, 2 MeV—the interactions they cause can become significantly more damaging biologically, justifying the higher weighting factor of 5. This accounts for the relative biological effectiveness (RBE) of protons compared to photons, recognizing that protons create dense ionization tracks and can lead to more complex DNA damage that is harder for cells to repair.

This reflects the understanding within the field of medical dosimetry that different types of radiation carry varying levels of risk, and it emphasizes the importance of