Application of a laser-wakefield driven monochromatic photon source to nuclear resonance fluorescence

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.