Diamonds have been used to detect ionizing radiation for a very long time, and it looks like they've now figured out a way to harness that to generate a very small current.

Here's a general explanation for how the detectors work: https://en.wikipedia.org/wiki/Semiconductor_detector

Here's some more info about using diamond as a netron detector: http://www.npl.co.uk/upload/pdf/091104_nuc_galbiati.pdf