Pencil
Pencil turns up in 2 fields: nuclear, lighting. Here is what it means to the people in each one.
Pencil in nuclear
A pocket ion chamber dosimeter shaped like a pen, read by looking through it at a light.
Slang for a self-reading pocket dosimeter, a small charged ion chamber in a pen-sized tube with a quartz fibre that moves across a scale as dose accumulates. The wearer reads it by holding it up to the light. Pencils back up TLDs for daily dose tracking where electronic dosimeters are not used, and they sit in emergency kits because they need no batteries.
"Pencil's reading 150, that's more than the job estimate, let's stop and figure out where it came from."
Pencil in lighting
A narrow, cone-shaped bundle of light rays diverging from or converging to a single point.
A geometric collection of light rays that share a common focal point, forming a narrow cone. In optical design, engineers trace these pencils through lenses and mirrors to calculate aberrations, focal lengths, and image sharpness. Unlike a broad beam, a pencil represents the specific light paths connecting one object point to one image point.
"The collimator is misaligned, causing the pencil of rays to hit the sensor at an oblique angle."