  The SuperNEMO experiment will search for neutrinoless double-beta decay
($0\nu\beta\beta$), and study the Standard-Model double-beta decay process
($2\nu\beta\beta$). The SuperNEMO technology can measure the energy of each of
the electrons produced in a double-beta ($\beta\beta$) decay, and can
reconstruct the topology of their individual tracks. The study of the
double-beta decay spectrum requires very accurate energy calibration to be
carried out periodically. The SuperNEMO Demonstrator Module will be calibrated
using 42 calibration sources, each consisting of a droplet of $^{207}$Bi within
a frame assembly.
  The quality of these sources, which depends upon the entire $^{207}$Bi
droplet being contained within the frame, is key for correctly calibrating
SuperNEMO's energy response. In this paper, we present a novel method for
precisely measuring the exact geometry of the deposition of $^{207}$Bi droplets
within the frames, using Timepix pixel detectors. We studied 49 different
sources and selected 42 high-quality sources with the most central source
positioning.
