Which factor affects accuracy due to the duration of the measurement?

• A. The sample's surface roughness
• B. The instrument's firmware version
• C. The duration of the measurement
• D. The display resolution

Answer: (C)

In XRF analysis, accuracy improves when you collect more photons. The number of detected X-ray counts follows Poisson statistics, so the uncertainty is proportional to the square root of the total counts. Relative uncertainty is roughly 1 over the square root of the total counts, meaning that longer measurement time increases the total counts and reduces the relative error. As a result, the peak areas and background are estimated more precisely, leading to more accurate concentration results.

Extending measurement duration is the direct way to influence this aspect of accuracy, as it boosts the signal-to-noise ratio. Shorter measurements can give higher statistical noise, making quantification less accurate. Note that factors like surface roughness, firmware version, or display resolution don’t change with measurement time in the same way; they affect data quality or processing in other ways, but not the counting statistics that improve with longer counting time.

So, longer measurement duration helps achieve greater accuracy by increasing the number of detected counts and reducing statistical uncertainty, assuming the sample remains stable during the measurement.