Ion Yields for Tetramethylgermane Exposed to X-rays near the Ge K-edge

R. A. Holroyd, J. M. Preses, and T. K. Sham

J. Phys. Chem. A 104, 2859-2864 (2000)

Abstract:

Free ion yields were measured for tetramethylgermane (TMG) in both the liquid and vapor phase and for Kr gas exposed to X-rays. The X-ray energy was varied across the K-edges of Ge and Kr, respectively. In Kr the relative W-value increases slightly at the K-edge, which is at 14.3 keV. In liquid TMG the observed ion yield drops at the Ge K-edge (11.1 keV) and shows two minima separated by 10 eV. This ion-yield spectrum is a mirror image of the absorption spectrum, as represented by the gas-phase ion-yield spectrum. The observation of such an inverted spectrum in liquids is shown to be due in large part to inefficiency of collection of charges. This is a consequence of the large Ge cross sections above the edge which concentrates the region of irradiation near the entrance window, increasing the local dose rate and enhancing recombination. The yield of excited states in mixtures of TMG and toluene drops at the Ge K-edge by the amount expected considering the large X-ray fluorescence yield.