Which isotope is used as the radiation source in XRF analyzers for lead paint inspection?

Which isotope is used as the radiation source in XRF analyzers for lead paint inspection?

• A. Cadmium-109 Isotope
• B. Cesium-137 Isotope
• C. Cobalt-57 Isotope
• D. Iridium-192 Isotope

Answer: (C)

The key idea is that XRF works by using a radiation source to excite the target elements so they emit characteristic X-rays that reveal their presence. For lead in paint, you want photons energetic enough to ionize lead’s inner shell (the K-shell). A source that emits photons around 122 keV, like cobalt-57, does this efficiently, producing the strong lead K-shell fluorescence needed for accurate lead measurement. The other isotopes listed either emit photons that are too low in energy to reliably eject K-shell electrons in lead (and thus produce weaker or unreliable lead signals) or are much higher in energy, where the photoelectric interaction becomes less probable and the fluorescence yield decreases. So, cobalt-57 provides the suitable energy for exciting lead in paint and generating detectable lead X-rays, making it the best choice among the options.

The key idea is that XRF works by using a radiation source to excite the target elements so they emit characteristic X-rays that reveal their presence. For lead in paint, you want photons energetic enough to ionize lead’s inner shell (the K-shell). A source that emits photons around 122 keV, like cobalt-57, does this efficiently, producing the strong lead K-shell fluorescence needed for accurate lead measurement. The other isotopes listed either emit photons that are too low in energy to reliably eject K-shell electrons in lead (and thus produce weaker or unreliable lead signals) or are much higher in energy, where the photoelectric interaction becomes less probable and the fluorescence yield decreases. So, cobalt-57 provides the suitable energy for exciting lead in paint and generating detectable lead X-rays, making it the best choice among the options.