Which isotopes are the sources of an XRF system?

The correct choice is based on the fact that Cobalt-57 and Cadmium-109 are both isotopes commonly used as sources in X-ray fluorescence (XRF) systems. XRF is a technique used to determine the elemental composition of materials through the emission of secondary X-rays from a sample when it is excited by a primary X-ray source.

Cobalt-57 is often employed in XRF applications due to its properties that make it a suitable source for exciting the fluorescence of certain elements. Its half-life and ability to emit X-rays in a useful energy range align well with the detection of various elements for analysis.

Cadmium-109 is another isotope used in XRF systems, known for its stable emission of X-rays at energies that are effective for exciting a wide range of elements. The dual-use of these isotopes in XRF systems enhances the versatility of the equipment and improves the quality of elemental analysis across diverse materials.

The other options include isotopes that are not typically used in XRF applications for various reasons, such as their energy levels, emission characteristics, or stability, which do not align well with the requirements of effective X-ray fluorescence analysis. Therefore, the combination of Cobalt-57 and Cadmium-109 is particularly effective and