What does the weighting factor (Wr) in the equation for REM represent?

The weighting factor (Wr) in the equation for dose equivalence, which is expressed in rems (Roentgen equivalent man), represents the type of radiation. The purpose of the weighting factor is to account for the different biological effects of various types of radiation on human tissue. Different types of radiation, such as alpha particles, beta particles, gamma rays, and neutrons, have different abilities to cause ionization and damage in tissues.

For instance, alpha particles, which are relatively heavy and carry a positive charge, are much more damaging on a per-particle basis than beta particles or gamma rays when they interact with biological tissues. By assigning a specific weighting factor to different types of radiation, the equation provides a more accurate representation of the potential biological harm from exposure.

In practice, this means that for calculating the effective dose received by a person, the absorbed dose is multiplied by the weighting factor corresponding to the radiation type, leading to a more nuanced understanding of risk. The weighting factor is essential in radiation protection and safety protocols to ensure that exposure limits account not only for the amount of radiation but also for its type and associated risks.