This video demonstrates the use of a condenser microphone to detect alpha particles from a variety of fairly intense sealed alpha sources. I explain why the mic is sensitive to radiation, and compare its (unintended) behavior as a radiation detector to that of purpose-designed radiation detectors that measure ionization. More details follow below:

THE MICROPHONE depicted in this video is the S3-47 sold in kit form by Microphone-Parts.com. It contains a clone of the Neumann K47 condenser capsule biased at about 60 volts and a preamplifier with a JFET impedance converter. Obviously, I have intended uses for the microphone besides just demonstrating this interesting radiation effect. I found the kit to be well-designed and very easily assembled.

OTHER MICROPHONES: I have observed this effect in a couple other (really cheap) condenser and electret microphones; there are also condenser / electret microphones where I don't observe the effect, probably because the grille or the internal capsule design blocks alpha radiation. I am sure this effect works better in principle if the grille is removed but I haven't tried that yet--there is a strong likelihood of electronic noise in designs where the grille forms a Faraday cage around the capsule. The effect will not work at all with dynamic / ribbon / carbon microphones as these work on completely different principles.

OTHER RADIATION SOURCES: Will this work with beta and gamma sources or x-rays? In principle, yes; however, the microphone capsule's geometry strongly favors high-LET radiations (and even for these, is far from optimal). In my attempts to detect beta and gamma sources I have not been successful.