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Velocity Selector and Mass Spectrometer Simulation

Velocity Selector and Mass Spectrometer Simulation

Velocity Selector and Mass Spectrometer

v16

Select ions by speed with crossed fields, then separate them by mass

Equations Off Teaching cues Off Dark mode Off

Sample

Isotope

Ion charge

Simulation controls

Speed1×

Velocity selector

Plate voltage, V100 V

Selector field, B₁50 mT

Analyser

Analyser field, B₂0.50 T

Display options

Show fields

Show rejected ions

Show radii

Show detector scale

Detector

Equations

Live values

Selector field, E Selected speed, E/B₁ Peak separation

The source produces ions with a range of speeds, about ±30% here. Two identical ions can behave completely differently in the selector simply because they entered at different speeds. In the selector the electric and magnetic forces oppose each other, and only ions travelling at v = E/B₁ pass through the slit undeflected. The rest are absorbed by the plates.

Selection does not depend on mass, so both isotopes get through. In the analyser they all have the same speed and charge, so r = mv/qB₂ depends only on the mass. The heavier isotope curves less and lands further down the detector.

Each ion lands 2r from the slit, so measuring that distance gives the mass.

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