  Since the discovery of nuclear gamma-rays, its imaging has been limited to
pseudo imaging, such as Compton Camera (CC) and coded mask. Pseudo imaging does
not keep physical information (intensity, or brightness in Optics) along a ray,
and thus is capable of no more than qualitative imaging of bright objects. To
attain quantitative imaging, cameras that realize geometrical optics is
essential, which would be, for nuclear MeV gammas, only possible via complete
reconstruction of the Compton process. Recently we have revealed that "Electron
Tracking Compton Camera" (ETCC) provides a well-defined Point Spread Function
(PSF). The information of an incoming gamma is kept along a ray with the PSF
and that is equivalent to geometrical optics. Here we present an
imaging-spectroscopic measurement with the ETCC. Our results highlight the
intrinsic difficulty with CCs in performing accurate imaging, and show that the
ETCC surmounts this problem. The imaging capability also helps the ETCC
suppress the noise level dramatically by ~3 orders of magnitude without a
shielding structure. Furthermore, full reconstruction of Compton process with
the ETCC provides spectra free of Compton edges. These results mark the first
proper imaging of nuclear gammas based on the genuine geometrical optics.
