19.3 Detection of radioactivity Two types of devices, Geiger counter and scintillation counters, are used to count particles emitted from radioactive nuclei.

Geiger counter A kind of ionization counter used to count particles emitted by radioactive nuclei, consists of a metal tube filled with gas, such as argon. Radioactive decay produces ion when moving through matter such as argon. This fast moving particle knocks off electron from argon. Speaker gives “click” sound for each particle.

Figure 21.9: A Geiger counter.

scintillation counter A device that detects nuclear radiation from flashes of light generated in a material by the radiation. Detector counts flashes of light.

Figure 21.10: A diagram of how a scintillation probe works. Return to slide 50

Half-life Time required for half of the original sample of nuclei to decay. 1000 nuclei, half life = 500 nuclei The shorter the half life, the more likely to decay Pa half life = 1.2 minutes U half life – 4.5 billion years Pa “hotter”, shows more reactivity

19.4 Dating by Radioactivity Radiocarbon dating or carbon-14 dating Based on the radio activity of carbon-14 which decays by beta particles.