Compton Scattering — iLearnSTEM Labs

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labs.ilearnstem.ca — Virtual Science Laboratories

Ontario Curriculum · Grades 9–12Beta

Compton Scatteringaccumulating

target electronλ₀ 50 pmE₀ 24.8 keVθ 90°counts 0/80λ′ …

Each count is one photon–electron collision, sampled with the Klein–Nishina cross section — the pink dots are photons that lost energy to a recoil electron.

Physics Lab 12 · Compton Scattering — λ′ = λ + (h/mc)(1 − cosθ), one collision per count · the spectrum sharpens as √N · drag to orbit, scroll to zoom

X-ray source

Incident wavelength50 pm · 24.8 keV

Shorter wavelength = harder photons. The Compton shift itself is a fixed number of picometres — only short photons make it a measurable fraction of themselves.

Beam intensity60%

Intensity is photons per second — it fills the spectrum faster but can never move the peak. Geometry alone decides the shift.

Goniometer

Scattering angle θ90°

The detector arm swings around the target. Moving it wipes the spectrum — a new angle is a new measurement.

Detector spectrum

λ₀ = 50 pmλ₀ + 10 pm

peak counts 0/80λ′ …

Cyan is the shifted Compton peak; grey is the unshifted line off bound electrons. Each bar is real counts — the peak sharpens as √N.

What the bench is doing

Counting at 8.2 counts/s — 0/80 in the shifted window. The peak emerges from the noise on its own.