the following examples that their concept and function are operatively similar the basic concept is to prevent either by interruption or by compensation the substrate based adverse effects of radiation and thereby mitigate the effect of transient photocurrent upon the silicon sos circuitry for the purpose of enhanced radiation hardness and performance the first apparatus of fig1 a 1b involves shielding in a silicon circuit on sapphire it is possible to make use of shielding electrodes or 34 guard 34 rings to isolate one region of the device from another region for example a p 34 channel stop 34 serves to isolate one n region from another n region for this to be effective one generally diffuses the p dopant through to the substrate then at least for moderate voltage excursions the two n regions are isolated a similar electrode geometry for a fet on sapphire is presented in fig1 a three long electrodes e 1 e 2 and e 3 are shown however the photo current flow of fig1 b raises the issue of whether or not electrode e 2 can shield electrode e 1 from electrode e 3 calculations may be made assuming the sapphire becomes temporarily conductive with a dose rate dependent resistivity these have shown that e 2 is not totally effective in reducing the current between e 1 and e 3 while there is some effect the desired isolation of electrode e 1 from electrode e 3 is not fully obtained the physical picture which emerged is as follows the total conductance between any two electrodes is due to a.