physicsfun on Instagram: "Personal Geiger Counter: this affordable detector will sense a wide range of invisible ionizing radiation using a Geiger-Müller tube the size of a ballpoint pen. Here the counter is clearly sensing the radiation from the Thorium 232 found in some (older) lantern mantles. Th232 is a naturally occurring radioactive element which decays to Lead (Pb208) through a complicated decay chain involving gamma, beta, and alpha particle emissions. This device is from Russian old sto