X-ray absorption in characterization of laser fusion targets

Many plastic or metal coated targets are opaque, so their thickness and thickness uniformity cannot be obtained by optical means. Therefore, we have built and tested a new system using monochromatic X-ray absorption measurements. This system is also able to perform non-destructive measurements of argon fill pressure in glass microballoons. The X-ray source is a diffraction tube with a chromium target and fine focus (0.4 x 0.8 mm2). Since monochromatic calculations are involved in this method, we use electronic discrimination to isolate the chromium Kα line (5.4 keV) from the bremsstrahlung spectrum. The detectors are xenon-filled proportional counters. The system is composed of two beams (10 μm in diameter), one used as a reference and the other as the measurement arm. A PET desk computer is coupled ot the experiment. We achieved a precision better than 10% for gold layers in the range of 0.1 to 1 μm, and better than 20% for argon pressures in the range of 5 - 13 bars