How Fast Is X-Ray Photon?

X-rays travel at light speed in vacuum but slow to about 95% of c in dense matter like bone. This subtle slowing is what allows X-ray imaging — denser tissue absorbs and slows photons differently, casting a clear shadow on the detector.

X-rays slow to 95% of c through bone — which is exactly what makes X-ray medical imaging possible.

• Slows to 95% of c in bone
• Wavelengths from 0.01 to 10 nanometres