Step-wedge spectrometer for pulsed X-ray sources

Summary form only given. High-current (/spl sim/10 kA), pulsed (/spl sim/25 ns), bremsstrahlung X-ray sources in the 100 keV to 2 MeV regime are commonly used to radiograph hydrodynamic physics experiments. Knowledge of the spectrum is useful both in improving source performance and image analysis. Consequently, we are developing a spectrometer for such sources. X-rays are detected in 25 channels, each comprising an X-ray filter, an LYSO scintillator and lead (side) shielding. A Monte Carlo calculation gives the spectral responses of the channels, which then allows unfolding the X-ray spectrum from the relative light outputs. Greatly complicating the application of such a scheme is the sensitive dependence of the unfolding to errors in both the data and in the frequency-response calculations. This is mitigated by tailoring the channel responses to be as far from linear dependence as possible. As in an earlier version of this system, filter thickness and material is varied to maximize the distinction of the low-end acceptance of the channels, with thicker, higher-Z filters giving a higher low-end "cutoff" similar that done by Carlson and Gorbics. The earlier spectrometer employed the same scintillator (sheet of LANEX Fast B) for all channels, but varying the thicknesses of the LYSO scintillators now adds some control of the high-end cut-off, along lines similar to Priedhorsky. Optimizing filter/scintillator thickness combinations to separate the spectral responses of the various channels are shown. Experimental data with a 1.5 MeV endpoint energy pulsed bremstrahlung source and the backing out an X-ray spectrum is also presented.