The Diocles laser at the University of Nebraska presents the possibility of producing a tunable, monochromatic X-ray source that has obvious applications in nuclear material detection. The pulsed and directional nature of this X-ray source makes traditional spectroscopy techniques for characterizing this source challenging. The large number of X-rays arriving at the detector in a short period of time would result in a high degree of pulse pileup, making the individual X-ray energy indistinguishable. In the technique presented in this paper, a series of attenuator materials will be placed in the path of the Xrays and the integral detector response will be measured. A series of detector response measurements with different attenuators will allow determination of the incident X-ray energy by using unfolding techniques.