What is used to calibrate an ionization chamber annually?

The calibration of an ionization chamber is essential for ensuring accurate measurement of radiation doses in medical settings and research. The National Institute of Standards and Technology (NIST) source is utilized for this purpose because it provides a reliable and traceable standard that is recognized nationally and internationally. NIST maintains a set of standards for various measuring devices and materials, including radiation detectors like ionization chambers. By using a NIST-calibrated source, facilities can ensure that their measurements are consistent and comparable to other laboratories and institutions.

NIST sources are specifically designed with known radioactive decay properties, allowing for precise calibrations that reflect the true output of the ionization chamber under standardized conditions. This is crucial for maintaining the accuracy and quality of radiation measurements, which affects patient safety and treatment efficacy.

Other options may not provide the same level of standardization and traceability. An internal radioactive source, while it can be used for specific measurements, does not guarantee the same calibration consistency or accuracy as a NIST source. A universal calibration source might sound useful, but it generally lacks the specific traceability that a NIST standard offers. Similarly, a gamma ray source could serve different purposes but does not specifically imply the traceability and reliability associated with NIST calibration practices.