In this paper , the inverse problem of determining an unknown source term in a parabolic equation with Neumann boundary conditions and final measured data is considered . Initially , the unknown source term is estimated in the form of a combination of orthogonal functions . Since this inverse problem is illposed , the Tikhonov regularization technique is applied to find a stable solution . Then , a Sinc-Galerkin system is assembled to solve the direct problem . The approximate solution displays an exponential convergence rate . At the end of the paper , the proposed method is tested on 2 examples .