Final answer:
In the context of CT scanning, the pencil thin section of the x-ray fan beam that strikes a single detector is known as a ray.
Step-by-step explanation:
The pencil thin section of the x-ray fan beam that strikes a single detector is called a ray. In the context of computed tomography (CT) scanners, X-rays are passed through a narrow section or slice of the patient's body over a range of directions. These rays are then registered by an array of many detectors on the opposite side. As the x-ray tube and detector array rotate together around the patient, multiple images are taken from various angles, and these images are processed by a computer to create detailed cross-sectional images, which can be further analyzed to produce three-dimensional views of the scanned tissues.