For Mev and sub-MeV gamma-ray astronomy or medical imaging, we have
developed an electron-tracking Compton camera (ETCC) consisting of a
gaseous Time Projection Chamber (TPC) and a scintillator. The TPC
measures the three-dimensional track and energy of a Compton
recoil-electron, while the scintillator measures the energy and position
of the scattered gamma ray. Therefore, the ETCC is able to reconstruct
Compton scattering event-by-event.
Since the angular resolution of the camera depends on an energy
resolution of the scintillator, we have adopted a LaBr3(Ce) that has an
excellent energy resolution. We have developed an 8 x 8 array of the
LaBr3(Ce) pixels with a pixel size of 5.8 mm x 5.8 mm x 15.0 mm (or 20.0
mm) in order to have position sensitivity for gamma rays. The array was
coupled to an 8 x 8 multi-anode PMT (Hamamatsu H8500), and the pixel
size was as the same as the anode size. The energy resolution of the
array reached 5.2±0.6% (FWHM) at 662 keV. Using the LaBr3(Ce) arrays,
the ETCC had an angular resolution of 4.2±0.3 degrees (FWHM) at 662 keV.