Mass Spectrometer: Step 3 - Mass Separation
In the last stage the ions, all with the same charge and velocity, enter a region of uniform magnetic field Bo. The field is perpendicular to the velocity, so the ions follow circular paths.
| F |
= |
qvBo |
= |
| mv2
|  |
| r
|
|
| The radius is |
r |
= |
| mv
| |
| qBo
|
|
Since v was given by E/B for the velocity selector, this is sometimes written as:
| r |
= |
| mE
| |
| qBBo
|
|
Everything is the same for the ions except for mass, so the radius of each circular path depends only on mass. The ions are collected after traveling through half-circles, with the separation s between two ions being equal to the difference in the diameters of their respective circles.
| s |
= |
2r2 - 2r1 |
= |
| 2(m2 - m1) v
| |
| qBo
|
|
In which direction is the magnetic field in the simulation above?
- Into the screen
- Out of the screen