Which of the following sources is the most appropriate for assessing dose calibrator constancy?

The most appropriate source for assessing dose calibrator constancy is cesium-137 (Cs-137). This choice is based on several factors related to the physical properties of the isotope and its suitability for this application.

Cs-137 is a gamma-emitting radionuclide that emits photons of energy at 662 keV, making it well-regarded for use in dose calibrators. Its characteristics offer a stable and distinct energy peak that allows for consistent measurements. Cs-137 has a half-life of about 30.1 years, which means it remains a reliable standard over a long period, reducing the need for frequent replacement of the source.

Moreover, maintaining the constancy of a dose calibrator is critical to ensuring accurate radioactivity measurements in nuclear medicine. The stable output characteristics of Cs-137 provide a useful benchmark for the performance of the calibrator, ensuring that it delivers accurate readings for a range of isotopes used in clinical practice.

In contrast, other isotopes such as cobalt-57 (Co-57), iodine-125 (I-125), and iodine-131 (I-131) are less suitable for this specific purpose. Co-57 has a lower energy peak at 122 keV, which may not provide as clear