A muon is like an electron, but 207 times heavier. When it slams into matter, it slows down like a bullet in a sandbank, and at every bend in its path it emits X-rays. Those X-rays tell you which atoms the muon encountered: that's the idea behind a technique called MIXE. It lets you peer inside an object without dismantling it, like an X-ray for materials.
Three computer programs (SRIM, GEANT4, and PHITS) calculated how muons stop in a layered lithium-ion battery. The battery is built from layers of different materials, like a layer cake. All three programs painted a similar picture: muons penetrate to a certain depth, and even sharp boundaries between layers don't throw off the calculation. An experiment on the GIANT spectrometer confirmed that the programs aren't lying.
Despite that error, PHITS correctly reproduces the brightness and shape of the spectrum — the pattern of X-ray lines. That means each element in the battery can be identified from this pattern. Just correct the energy shift, and the program becomes a precise tool for non-destructive material analysis — from batteries to ancient artifacts.
Muons are born in the upper atmosphere when cosmic rays smash into it. About one muon passes through your palm every second.
In Arthur C. Clarke's novel The Light of Other Days, characters use particles to see through any barrier — muon analysis is close to that idea.