What is the unit used to measure the health effect of low levels of ionizing radiation on the human body?

The unit used to measure the health effect of low levels of ionizing radiation on the human body is the Sievert (Sv). The Sievert quantifies the biological effects of radiation, taking into account the type of radiation and the sensitivity of different tissues. This unit is particularly important in the context of assessing radiation exposure and risk to human health, specifically for its potential to cause harm or increase the likelihood of cancer.

In radiation safety, it's critical to not only measure the amount of radiation absorbed (which is what Gray (Gy) does) but also to evaluate the associated biological risk of that absorbed radiation. Sieverts provide this biological weighting, making it essential for understanding health implications.

While the Roentgen Equivalent Man (rem) was used in the past for similar purposes, it has largely been replaced by the more current and standardized measure of the Sievert in modern radiation protection practices. The Gray (Gy) is focused on measuring absorbed dose regardless of biological effects, and the Curie (Ci) measures radioactivity rather than the human health effects of radiation exposure. Thus, the use of Sieverts aligns best with assessing health risks from ionizing radiation.