For that, you need something like this gamma-ray spectroscope. Dubbed the Pomelo by [mihai.cuciuc], the detector is a homebrew solid-state scintillation counter made from a thallium-doped cesium ...

Preparing a pomelo isn’t just a matter of cutting it in half equatorially (as opposed to slicing it through the stem ends) and scooping out the flesh, as you would do with a grapefruit.