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Recent investigations conducted at the Omega Facility have employed CMT PCD’s, compared to diamond PCD’s, as a diagnostics x-ray detection tool to conduct inertial confinement fusion (ICF) experiments. Development of the CMT PCD’s for measuring x-ray emissions from the fusion experiments will enhance the x-ray measurements. The properties of this material include a very large resistivity, good electron transport, and an inherently very high x-ray stopping power, for which the photoelectric effect shows a near-flat, approximately 100% absorption spectrum up to ~50 keV. Research conducted at LLE indicates that CMT PCD’s are a viable option that will allow accurate, temporal characterization of x-ray transients, especially at medium to high spectral ranges, generated during the ICF event.

For detector preparation and experimental setup, Cd_1–xMn_xTe (x = 0.05) single crystals, doped with V, were grown using a vertical Bridgman method and, subsequently, annealed in Cd vapor for the highest resistivity (~10¹⁰ Ωcm) and a good mobility-lifetime product (several 10^–4 cm²/ V). The 1- and 2.3-mm-thick detectors were placed in the same housing used for two 1-mm-thick diamond PCD’s. Each device was preceded by a 7.6-μm-thick Be x-ray filter with 37% x-ray transmission at 1-keV cutoff energy. The response amplitudes and rise times of the CMT PCD’s were measured and proved to be comparable with the diamond detector’s performance, while their decay times were an order of magnitude longer (in the 5- to 10-ns range).

The OMEGA shots designed to test the performance of the CMT PCD’s employed empty plastic-shell targets, which resulted in x-ray emissions from both the corona and the imploded shell, recorded as two peaks in time. The incident-beam illumination was comprised of 1-ns-long, square-shaped pulses with total energies ranging from 2.3 kJ to 22.6 kJ. The initial laser heating of the target created a hot corona, causing the first temporal peak, while the second temporal peak was caused by x-ray emission from the core formed by the compressed plastic shell. For comparison purposes, testing was performed using x-ray photons with energies above 1 keV, optimal for the diamond PCD. According to simulations for 1-mm-thick crystals at x-ray energies >10 keV, diamond absorption efficiency drops to <50%. For CMT, however, the same absorption drop occurs at ~100 keV, and one can observe a near-perfect, 100% absorption, up to 50 keV.