What is placed onto the output phosphor to prevent light from scattering back towards the photocathode in an image intensification tube?

The correct choice is a thin sheet of aluminum, which is used in an image intensification tube to prevent light from scattering back towards the photocathode. In this context, the role of aluminum is crucial due to its effectiveness as a barrier that allows for efficient transmission of light while minimizing unwanted reflections.

The output phosphor emits light when it is stimulated by the incident electrons. If this emitted light were to reflect back toward the photocathode, it would result in reduced image clarity and degradation of the image quality. By employing a thin sheet of aluminum, which is lightweight and possesses good reflective properties, the design minimizes the chances of backscatter, thus ensuring that the light travels in the desired direction for optimal image enhancement.

This function is essential in the overall efficiency of the image intensifier, where clarity and brightness of the final image are critical for accurate diagnostics. Therefore, the choice of a thin sheet of aluminum plays a significant role in the performance of fluoroscopy equipment.