NYT:
This month, at the Princeton Plasma Physics Laboratory, physicists and engineers built [model train] tracks inside one of its fusion reactors and ran a toy train on them for three days.
[…]
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.
“We needed to refine the calibration technique to make sure we are measuring our neutrons as accurately as possible
Awesome.
Lemkin 