S. Grévy

A charged particle beam is like a jet of water from a hose: it can be narrow or diffuse, steady or curved. To know exactly where particles are headed, you need a sensitive screen. In the WISArD experiment at ISOLDE, CERN's accelerator, that screen is a compact detector based on microchannel plates.

Imagine a multi-story building where protons and neutrons live on each floor. The floors are energy levels, and usually there's a stairwell of a certain height between the sixth floor and the one above — the so-called gap. In the oxygen-20 nucleus, this gap acts as a barrier that particles find hard to cross.