Abstract: A high resolution directional gamma ray detector includes a thin piece of foil, such as tantalum, which reacts with gamma rays incident to the edge of the foil to generate electron/positron pairs. Gamma rays originating from directions other than a direction of interest are shielded from the foil by shielding plates. An opening between the foil by shielding plates. An opening between two collimating plates permits passage of gamma rays originating from a direction of interest and allows gamma rays originating from a direction of interest to react with the foil. The generated electron and positron cause ionization in a plurality of cells. Signals resulting from these ionizations are processed by an electronic computation system through the use of coincidence processing to determine whether the signals are the result of a reaction between the foil and a gamma ray which passed through the collimator opening.