Half-life and Carbon Dating 7.2 Half-life and Carbon Dating

Today’s lesson Radioactive decay Half-life Half-life activity Carbon dating Radioisotope dating Homework: Textbook: p. 302-311 Workbook: p. 129-136 7.2: Half-life Worksheet

Recall from last lesson: Unstable particles split apart, releasing smaller particles and energy RADIOACTIVITY: the emission of energy or particles caused by the spontaneous disintegration of atomic nuclei Radioactive decay: the process in which unstable nuclei lose energy by emitting radiation in the form of particles and energy

Radioactive decay We can predict whether an atom will or will not decay based on whether the isotope is stable or not However, we cannot predict precisely when the atom will decay because the decay event itself is spontaneous We can calculate the probability of whether it will decay over a given time by examining large quantities of the radioactive atom and observing the pattern of decay Half-life: ________________________________________________________ ________________________________________________________

0 Half-lives Example: Carbon Carbon-14 undergoes radioactive decay to become nitrogen-14 0 Half-lives

1 Half-life 2 Half-lives

3 Half-lives 4 Half-lives

# Half-lives % 𝑪 𝟏𝟒 % 𝑵 𝟏𝟒 Ratio of 𝑪 𝟏𝟒 to 𝑵 𝟏𝟒 % 𝑪 𝟏𝟒 % 𝑵 𝟏𝟒 Ratio of 𝑪 𝟏𝟒 to 𝑵 𝟏𝟒 1 2 3 4 The half-life of Carbon-14 is 5730 years. This means after 5730 years, only half of a sample of Carbon-14 will remain. How many years have passed if only 6.25% of a sample of Carbon-14 remains?

Carbon dating The ratio between carbon-12 and carbon-14 in nature remains constant Carbon-1298.93% STABLE Carbon-141x 10 −10 % UNSTABLE In a living organism, as the carbon-14 decays it is replenished by constantly eating new carbon (food) However, once an organism dies the carbon-14 will decay and over time, will become less and less abundant compared to carbon-12 By comparing the ___________ between carbon-14 and carbon-12 in organic remains, we can estimate _____________________________ __________ and, therefore, ___________________________________

Example You are examining the remains of a beaver and you find that the proportion of carbon-14 to carbon-12 is only 12% of what you would find in a living beaver. How long has the beaver been dead?

Radioactive dating Carbon dating has limitations: It can only be used to date ______________________________ Only accurate/useful for samples up to_______________________ Can use a similar idea to date other substances (e.g. Potassium-40 clock)