Which fault produces a coned image during exposure to ionising radiation?

A coned image during exposure to ionising radiation typically occurs when the x-ray beam is not properly aligned or centered to the film. When the beam is misaligned, it can result in a focal spot that is not uniformly covering the film, leading to certain areas being underexposed or overexposed, hence creating that coned appearance. This issue is critical because proper alignment is necessary to ensure that the entirety of the area of interest is accurately captured on the radiograph.

The other scenarios may cause other types of imaging issues or artifacts. For example, placing the film backwards can result in a reversed image, patient movement may cause blurring rather than a coned effect, and an insufficient tube angle could potentially cause distortion without specifically leading to a coned image. Thus, incorrect alignment of the beam is the key factor responsible for producing a coned image.