therefore absorbs very little x ray radiation when deposited in thin layers additionally owing to its high melting temperature t c 1875 u00b0 c its diffusion coefficient to selenium at room temperature is very low this pay prevent formation of a cr u2014 se alloy layer that could significantly degrade imager performance by creating a large and unstable dark current signal having the top electrode be too thick or too thin may reduce structural integrity during manufacture and or operation and or increase x ray absorption level to an unacceptable level therefore selecting an optimal top electrode thickness is beneficial through experimentation it has revealed that a layer of chromium within the range of about 150 angstroms to about 2 000 angstroms produces satisfactory results and it is believed that a layer of chromium within the range of about 50 angstroms to about 10 000 angstroms would also produce satisfactory results ito and al in elemental form or as the predominant metal in an alloy with each other or with other elements also are believed to be examples of suitable materials another consideration is thermal expansion compatibility with selenium which may impose conditions on the composition thickness or formation technology of the top electrode the ability to rely on transistor leakage current to avoid breakdown under the expected operating conditions an x ray imaging panel may be surprising given common assumptions in x ray imaging technology for example in mammography uses of the prior art panel illustrated in fig1 that had been commercially available it had been believed that without a charge barrier layer 102 such a high amount of charge would accumulate at the individual signal storage capacitors 112 that the capacitor voltage would rise to a level sufficiently high to damage the.