[en] An experimental facility was established at LLL to characterize radiation fields produced by a variety of sources and transmitted through various shielding materials. Specific techniques for acquiring and reducing continuous gamma-ray energy spectra are discussed including NaI(Tl) detectors. Use of several detector sizes allowed study of a wide variety of source intensities and calculation of response matrices for a number of collimated detector configurations. A computer program to perform the data reduction by an iterative unfolding process is described. The reduction technique discloses the continuous gamma-ray energy spectrum over the range 0.1 to 8 MeV as opposed to the traditional peak intensity analysis. 11 references