  We have developed a position-sensitive scintillation camera with a large area
absorber for use as an advanced Compton gamma-ray camera. At first we tested
GSO(Ce) crystals. We compared light output from the GSO(Ce) crystals under
various conditions: the method of surface polishing, the concentration of Ce,
and co-doping Zr. As a result, we chose the GSO(Ce) crystals doped with only
0.5 mol% Ce, and its surface polished by chemical etching as the scintillator
of our camera. We also made a 16$\times$16 cm$^2$ scintillation camera which
consisted of 9 position-sensitive PMTs (PSPMTs Hamamatsu flat-panel H8500), the
each of which had 8$\times$8 anodes with a pitch of 6 mm and coupled to
8$\times$8 arrays of pixelated 6$\times6\times$13 mm$^3$ GSO(Ce) scintillators.
For the readout system of the 576 anodes of the PMTs, we used chained resistors
to reduce the number of readout channels down to 48 to reduce power
consumption. The camera has a position resolution of less than 6mm and a
typical energy resolution of 10.5% (FWHM) at 662 keV at each pixel in a large
area of 16$\times$16 cm$^2$. %to choose the best scintillator for our project.
  Furthermore we constructed a 16$\times$16 array of 3$\times3\times$13 mm$^3$
pixelated GSO(Ce) scintillators, and glued it to a PMT H8500. This camera had
the position resolution of less than 3mm, over an area of 5$\times$5 cm$^2$,
except for some of the edge pixels; the energy resolution was typically 13%
(FWHM) at 662 keV.
