Choo-Chooing Along to Aid in Measure of Neutrons

This month, at the Princeton Plasma Physics Laboratory, physicists and engineers built tracks inside one of its fusion reactors and ran a toy train on them for three days. It was not an exercise in silliness, but in calibration. The modified model of a diesel train engine was carrying a small chunk of californium-252, a radioactive element that spews neutrons as it falls apart