Detection of Radioactivity and the Concept of Half-life

19.3

Geiger-Müller Counter

Detects high energy ions from radioactive decay

Uncharged Argon gas is found inside the Geiger counter Ions send electrical pulse Geiger counter counts how often the

pulses are happening

Scintillation Counter

Instrument that detects radioactive decay

Every time decay events occur, the detector senses the flashes of light

Alternate way of detecting decay

Half-life

An important characteristic of a radioactive nuclide

Half-life: the time required for half the original sample of nuclei to decay

Lower half-life means more activity Ex: a certain radioactive sample

containing 1000 nuclei at a given time and 500 nuclei 7.5 days later, this radioactive nuclide has a half life of 7.5 days

Half-life

Example: 1 mole of Rubidium-223 becomes .5 mole of Rubidium-223 after 12 days 12 days would be the half life of

Rubidium-223 The sample would be .25 mol of

Rubidium-223 after 24 days

Dating by Radioactivity

19.4

Radiocarbon Dating

Radiocarbon dating: a technique for dating ancient articles made from wood or cloth Originated in 1940’s by Willard Libby

Radiocarbon dating is based on the radioactivity of C-14, which decays by -particle production Carbon-14 is continuously produced and

decomposed through particle production. Creating a constant amount of C-14 in

atmosphere

Radiocarbon Dating (cont.)

Used to date wood and cloth artifacts Every plant has Carbon-14, and there is

a constant amount of Carbon-14 in the atmosphere

The amount of Carbon-14 that is present in the artifact is compared to the amount found in the atmosphere

the half-life of Carbon is known to be 5730 years old