Which dosimeter is the primary standard of absorbed dose?

The primary standard of absorbed dose is represented by the graphite calorimeter or water calorimeter. This type of dosimeter is used to measure the amount of energy deposited in a medium by ionizing radiation, which directly correlates to the absorbed dose.

Calorimeters are precise instruments that measure the temperature change in a substance (such as water or graphite) due to the absorption of radiation. By understanding the energy deposited and the specific heat capacity of the medium, one can accurately calculate the absorbed dose. This method is regarded as a primary standard because it provides a definitive measurement that can be traced back to the International System of Units (SI), ensuring consistency and reliability in dose measurements.

In contrast, while other dosimeters like ionization chambers and thermoluminescent dosimeters are essential in clinical settings for routine dose measurements, they are not considered primary standards. Their measurements can be influenced by various factors, such as calibration against a primary standard or environmental conditions, which makes them secondary standards rather than direct measures of absorbed dose like calorimeters.