Pinpointing Time C1.5

What is Radioactivity? Marie Currie discovered radioactivity – the emission of energy from the nuclei of unstable atoms as the change to become more stable. Radioactive decay – the breaking down of the nuclei into a stable nuclei and particles Half-life – time it takes for half of the original nuclei (parent) to break into the stable nuclei (daughter). Mass spectrometer – instrument used to detect the amount of atoms present in a sample

Ernest Rutherford Rutherford built on the work of Marie Curie He found that radon-220 was unstable and spontaneously changed into polonium. As it changed it released energy When we discuss radioactivity we often refer to two isotopes are often referred to: Original unstable atom called the parent isotope More stable product called the daughter isotope

What Is Radioactive Dating Scientists can use radioactive elements and decay curve to predict the date of a sample. (pg 8 of your databook or pg. 557 of the text) Write out the decay reaction using pg 8. Parent  Daughter + particles + energy If necessary determine the percentage of parent remaining by subtracting from 100 Use the decay curve to determine the half-lives Multiple the half-lives by the years in one half life (pg. 8) to determine the absolute age Absolute age = half lives x years/one half life

An Example of Finding an Age A zircon rock has 30% of lead 206 238 92 U 

Constructing A Decay Curve Pg. 320

Assignment Add the dates to your timeline Practice Questions  Do these! 1.5 Questions Pg. 324 #1-6 C1.0 Quiz  Tomorrow