experimental physics - How can a charge of a particle be determined through its cloud chamber photograph?

Specifically in reference to Carl Anderson's famous cloud chamber photograph providing evidence of a positron. Any insight is appreciated.

Answer

In that experiment there exists a magnetic field perpendicular to the plane of the photo.

The motion of the charged particle in a magnetic field is used , equating the centrifugal with the centripetal force one gets

Bqv=mv^2/R

where B is the magnetic field, q is the charge ( with its sign) v the velocity m the mass and R the radius.

From the incoming direction and the right hand rule one knows the charge of the particle, in this case it has to be positive from the setup.

From the curvature one gets the momentum , thus the energy.

There exist ionization curves for a given particle mass

Ionisation is proportional to the number of ions scattered off as the particle moves through the cloud or bubble chamber, and is a function of the mass.

From the ionization characteristic for the measured energy, it could not be a proton, (at that small momentum the proton would have a much thicker ionization deposit and subsequent energy loss) it was consistent with an electron track which confirmed it as the proposed by Dirac positron.