What are the two radioactive sources commonly used in XRF devices?

The answer is based on the common use of radioactive isotopes in X-ray fluorescence (XRF) devices. Cobalt-57 and Cadmium-109 are both utilized due to their properties that are effective for non-destructive testing and analysis.

Cobalt-57 emits X-rays that can effectively excite elements present in a sample to emit fluorescent X-rays back, which are then detected and analyzed to determine the elemental composition of the material. Cadmium-109, similarly, provides a fluorescent X-ray source that is particularly useful for detecting low atomic number elements. Both isotopes are favored in XRF applications because of their ability to produce consistent and reliable signals for accurate measurement.

In contrast, other options involve isotopes that are not typically used for XRF applications. For instance, Lead-210 is more associated with environmental radioactivity and health concerns related to lead exposure rather than for excitation purposes in XRF. Uranium-238 and Radon-222 are primarily known for use in other types of nuclear applications and environmental studies, while Cesium-137 and Barium-133 are also not standard in the XRF context as they belong to other forms of analysis or industrial applications. Thus, Cobalt-57 and Cadmium-109 are established