In reactor design there is a requirement for a practical and economic method of predicting gamma-ray spectra throughout bulk shields. The commonly used build-up factor technique suffers the disadvantage of not predicting primary physical quantities, and the more sophisticated transport methods require considerable computer time and expertise to be effective. In the method developed here, an order of scattering model has been used with a spatial cell scheme and an energy multigroup system, but the usual limitation of computational complexity has been overcome by an angular approximation. An equilibrium property in the behavior of the angular penetration spectra has been incorporated in an anisotropic scatter approximation which tends, in the low energy limit, to become isotropic. The code has been tested over a range of penetrations and source energies, and the results are compared with the Monte Carlo method; similar results through an interface are given. Extension of the model to more complex geometries has been considered briefly.