I made the recordings and the images seen in the video.
Sounds made using a GS1100A from GammaSpectacular.com, a Radiation Sensors SPA38 from SpectrumTechniques.com, sources from SpectrumTechniques.com (and other places), software from PRA
The gamma energies are detected by the NaI(Tl) detector and converted into pulses of electricity, proportionate to their energy (low energy, low voltage, high energy, high voltage). The spectrometer converted these to sound. The higher the energy, the higher the pitch of the sound.