1. What XRF Really Sees

Many people think XRF checks the whole material — actually, it doesn’t. The X-ray only hits a tiny area, called the spot, usually 0.1–3 mm in diameter. The fluorescence signal penetrates just a few dozen micrometers below the surface.

In other words, the instrument only “sees” a very small part of the surface. If that small area is not representative of the whole material, test result will not be stable or accurate.

2. Why Uniformity Matters

Pureray's FP algorithm assumes that the sample is uniform. Once this assumption fails, all absorption and enhancement calculations become unreliable — even the best instrument cannot correct for this physical limitation.

Typical signs of non-uniformity include:

Different results from different spots on the same sample

Inconsistent readings across repeated tests

Average value appears normal but repeatability is poor

3. Common Cases of Non-Uniform Samples

4. How to Check if a Sample Is Uniform

Multi-point measurement: If the standard deviation is higher than normal repeatability → the sample is not uniform.

Large-spot scanning: Use a larger focal spot to obtain a more representative average.

Microscopic observation: Check for particles, solder joints, or oxide layers.

Polish or scrape: Compare the surface with the interior.

5. How to Minimize Errors from Non-Uniformity

Sample preparation:

Alloy: Remelt or polish before testing.

Powder: Grind, mix, and press into pellets.

Liquid: Filter, stir, and avoid settling.

Testing:

Use the camera to locate the test point.

Perform multi-point measurements and calculate the average. Pureray's True FP algorithm supports multi-point analysis and automatically calculates the average and RSD. 

For non-uniform samples, use large-spot or area-scan mode.

Data analysis:

Calculate the standard deviation (σ): If σ is noticeably higher than instrument repeatability, the sample is non-uniform.

6. A Common Misunderstanding

“Why does my analyzer give two different results for the same sample?” This is usually due to physical differences, not testing errors. The surface and interior may differ; solder and base metal may differ; oxidation or polishing changes the surface.

7. Conclusion

Uniformity is not just a testing condition — it is the foundation that makes testing meaningful. XRF gives accurate results only when the sample is uniform; otherwise, the calculation loses validity.

Tip: Always ask one question before analysis —“Is my sample truly uniform?”