  Suspensions of superheated superconducting grains are a detecting composite
material. Each grain in the supension is a microcalorimeter with an energy
threshold defined by its equatorial magnetic field for a given temperature. The
higher the matrix density, the larger the gamma stopping power. For several
years, cylindrical cells of such suspensions about 2 cm long and 0.4 mm in
diameter can be read out in real time. As a result, using two independent
cells, one can record a time coincidence between them. This could be
potentially very useful for positron cameras where two diametrically opposite
cells are simultaneously knocked by 511 keV gammas. This paper, based on the
state of art in SSG in high density matrix, discusses such a feasibility.

Instrumentation and Detectors