The resolution of a SPECT system for Tc-99m is 13 mm. The crystal is 1 cm thick. The intrinsic resolution of the crystal and electronics is 8 mm. The collimator septa is 0.3 mm thick. The collimator is made of lead. The distance of the radioactive source from the collimator surface is 70 mm. What must the length of the collimator septa be?

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