Which readings do not require substrate bias correction?

Which readings do not require substrate bias correction?

• A. Readings of 4.0 mg/cm2 or higher.
• B. Readings below 1.0 mg/cm2.
• C. All readings require correction.
• D. Readings exactly 1.0 mg/cm2.

Answer: (A)

Substrate bias correction is about adjusting for how the underlying material affects the reading when using XRF to measure lead in a coating. When the coating is thick enough, the XRF signal comes predominantly from the lead in the paint itself, and the substrate’s influence becomes negligible. In that case, applying a substrate bias correction isn’t necessary. The threshold used in practice is around 4.0 mg/cm2 or higher, where the coating signal dominates and the correction would not change the result meaningfully. If the coating is thinner (below this threshold), the substrate can bias the reading more, so correction may be needed. That’s why readings of 4.0 mg/cm2 or greater do not require substrate bias correction, while lower readings may.

Substrate bias correction is about adjusting for how the underlying material affects the reading when using XRF to measure lead in a coating. When the coating is thick enough, the XRF signal comes predominantly from the lead in the paint itself, and the substrate’s influence becomes negligible. In that case, applying a substrate bias correction isn’t necessary. The threshold used in practice is around 4.0 mg/cm2 or higher, where the coating signal dominates and the correction would not change the result meaningfully. If the coating is thinner (below this threshold), the substrate can bias the reading more, so correction may be needed. That’s why readings of 4.0 mg/cm2 or greater do not require substrate bias correction, while lower readings may.