Why 2θ in XRD graph instead of θ?

Why 2θ in XRD?

Two types of goniometers used in XRD analysis:

1- θ:θ Scan
2- θ:2θ Scan

This post explains why there is 2θ in XRD technique with the help of θ:θ Scan setup.

*θ:θ Scan*:

In a θ:θ instrument, the sample is FIXED and the x-rays tube rotates at a rate θ°/min (clockwise) and the detector rotates at a rate of θ°/min (anti-clockwise), see the video.

Here, in this case, we usefully see the XRD graph with 2θ value from 10° to 180°

Look at the video, θ is the incident angle between x-ray source and parallel planes of atoms NOT with the sample surface!. Similarly, θ is also the angle between the Reflected x-rays and parallel planes of atoms.

On the other hand, 2θ is the diffracted (scattered) angle between the transmitted x-rays and reflected x-rays. or 2θ is the angle between the transmitted x-rays and the detector!

The incident angle, θ is ALWAYS ½ of the detector (scattered or diffracted) angle 2θ.

The following questions are often asked regarding 2θ in XRD

Why there is 2θ instead of θ in the XRD technique?
Why do we use 2θ in the XRD spectrum/plot/graph?
Why 2θ?
Why the 2 theta?
What is 2θ in X-ray powder diffraction (XRD)?
In XRD, why is 2-theta used instead of theta?
Why is the angle 2 theta in XRD?
Why are we taking 2θ instead of θ in X-ray powder diffraction (XRD)
.
.
.
.
These are the most asked questions in the XRD technique, and I know it is very basic, but still, many researchers need it.

For the information, below is the detail for θ :2θ Scan

θ :2θ Scan: - Rigaku RU300

In θ :2θ instrument or arrangement, the x-rays tube is fixed, the sample rotates at θ°/min (~5° to 45°) and the detector simultaneously rotate at 2θ°/min (~10 to 90°).