The adjoint gamma transport theory method is used to analyze the postaccident gamma detector data from the Three Mile Island Unit 2 (TMI-2) reactor lower head. It is concluded that there are two layers of materials at position L-11 of the TMI-2 reactor lower head. The lower layer contains predominantly nonfuel materials and the upper layer contains predominantly fuel. It is also concluded that 137Cs, 137mBa, 60Co, and 154Eu have the highest contribution to the detector signal. Finally, it is shown that the detector field of view is very small; hence, further evidence is needed to generalize these results to the remainder of the TMI-2 lower head.