The attached visual shows the behaviour of the components of the radioactivity when it passes through a magnetic field established between the poles of an electromagnet.
Lorentz's law tells us the value and the direction of the force on the positive charge.

In the attached visual a radioactive emission is made to pass through an electric field created between two plates charged with opposite charges.
The unequal force exerted on each component gives them a different acceleration and separates them.