A novel <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si0022.gif" overflow="scroll"><mml:mi>γ</mml:mi><mml:mtext>‐</mml:mtext><mml:mi>ray</mml:mi></mml:math> imaging method for the pulse-shape characterization of position sensitive semiconductor radiation detectors