What isotope is used to calibrate a well-counter?

The isotope that is commonly used to calibrate a well counter is Cesium-137 (Cs-137). Cs-137 emits gamma rays with a specific energy of approximately 662 keV, which makes it an ideal choice for calibration because it allows for accurate measurements of detector response across a range of energies. This isotopic source provides a reliable benchmark since the emitted gamma rays can be easily detected and quantified by the well counter, ensuring that the system is correctly calibrated for clinical and research applications.

In calibration procedures, using a consistent source like Cs-137 helps in maintaining the accuracy and reproducibility of the measurements, which is crucial in any quantitative analysis involving radiolabeled substances. Its long half-life (about 30 years) and the ease of obtaining it for calibration purposes further enhance its suitability.

Other isotopes like Co-57, Eu-152, and Na-22 may have specific uses in different types of measurements or quality control processes but are not as widely adopted for well counter calibration specifically due to factors such as energy emission characteristics or availability.