Nuclear resonance fluorescence is of particular interest to the detection of special nuclear material (SNM) where isotopic characterization is paramount. In addition to photons emitted by resonance de-excitation, there will also be a significant amount of backscattered photons that will distort the NRF signal. The backscattered spectra must be characterized in order to design a detection system that maximizes the material identification probability. However, to our knowledge the cross-sections for nuclear resonance absorption do not exist in any version MCNP. Therefore, a novel method is applied here to reproduce the measured results from Bertozzi et al. using bremsstrahlung X-rays. The NRF signal this source was compared with the response from the University of Nebraska (UNL) quasi-monochromatic X-ray source to compare the performance on a per source photon basis. An absolute comparison of each source is left for future work. The results of the simulations show that the UNL source would have a higher efficiency on a per source photon basis by a factor of approximately 170.