A mass spectrometer is a scale for single atoms. It strips an electron off each atom to make an ion, hurls the ions through a known voltage so they all carry the same energy, and then bends them through a magnetic field. The Lorentz force on a moving charge is always sideways to its motion, so it curls each ion into a circle — and because a heavier ion is harder to turn, it swings on a wider arc. One element enters the magnet and a fan of separate beams comes out, one for every isotope.
This exhibit runs that physics exactly. Every ion gains the same kinetic energy qV = ½mv², so the lighter ones leave the accelerator faster; in the field each follows a circle of radius r = mv/(qB) = √(2mV/q)/B, and the landing point on the detector scales as √(m/q). Choose neon and the famous ²⁰Ne / ²²Ne doublet splits apart on the plate — the very measurement with which Francis Aston proved in 1919 that a single element can be a mixture of isotopes, work that won him the Nobel Prize. Switch to xenon for a forest of nine peaks, raise the field to pull the spectrum inward, or open the source energy spread and watch the lines blur, just as real resolution limits do.
Two detectors are wired up: a photographic plate that records every mass at once, the way Aston did it, and a single Faraday cup that sits at a fixed radius while the field is swept, so each isotope crosses it in turn and paints the peak spectrum every modern instrument prints. The same dance of fields and forces — accelerate, deflect, detect — is the one you can wire up gate by gate in DigiSim’s Logic Lab.
Specifications
- Principle
- Lorentz force bends ions; r = √(2mV/q) ⁄ B
- Separation
- Landing position ∝ √(m/q) — isotopes fan apart
- Samples
- Neon, chlorine, xenon, lead — real isotope abundances
- Simulated
- Exact ion optics, live plate exposure + Faraday sweep
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