polonium halos

The centroid of the densest portion of the ring. Sheesh.

Not at all like the ring. The ring density is a Gaussian distribution. Like so:You are ignoring a fundamental fact.The position of the densest portion of a ring in an image is a function of the energy of the particles emitted.The position of the edge of a ring in an image is a function of the energy of the particles emitted and the medium through which they traveled and the resolution of the image … and probabvly a few other things.Unless you incude all those variables in your "determination" of the edge postion, your detemination is less accurate than looking for the distribution's peak. "This case" as you presented it is irrelevant.