  Imaging of nuclear gamma-ray lines in the 1-10 MeV range is far from being
established in both medical and physical applications. In proton therapy, 4.4
MeV gamma rays are emitted from the excited nucleus of either 12^C^* or 11^B^*
and are considered good indicators of dose delivery and/or range verification.
Further, in gamma-ray astronomy, 4.4 MeV gamma rays are produced by cosmic ray
interactions in the interstellar medium, and can thus be used to probe
nucleothynthesis in the universe. In this paper, we present a high-precision
image of 4.4 MeV gamma rays taken by newly developed 3-D position sensitive
Compton camera (3D-PSCC). To mimic the situation in proton therapy, we first
irradiated water, PMMA and Ca(OH)_2 with a 70 MeV proton beam, then we
identified various nuclear lines with the HPGe detector. The 4.4 MeV gamma rays
constitute a broad peak, including single and double escape peaks. Thus, by
setting an energy window of 3D-PSCC from 3 to 5 MeV, we show that a gamma ray
image sharply concentrates near the Bragg peak, as expected from the minimum
energy threshold and sharp peak profile in the cross section of
12^C(p,p)12^C^*.
