Intro to HalfLife PhET Lab (Radioactive Dating Game).
Introduction: Dead things decay into simpler molecules. Radioactive particles decay. Is it the same kind of decay? What does it mean when a substance is radioactive? In this simulation, you will investigate the concept of halflife.
Some handy vocabulary for you to define: (use your notes, your book, or the internet)
Neutron _______________________________________________________________________________________________
Isotope _______________________________________________________________________________________________
Radiocarbon Dating______________________________________________________________________________________
HalfLife _______________________________________________________________________________________________
Decay (as used in halflife)_________________________________________________________________________________
Carbon14…what does the “14” represent? ___________________________________________________________________
Procedure: PhETàPlay with the Sims à Chemistry à Radioactive Dating Game
 Take some time and play with the simulation. Those atoms are radioactive! How cool is that?!
 How many protons does Carbon14 have? _____________ (hint…what is its atomic number?)
 How many neutrons does Carbon14 have? _____________ (hint: what is the mass?)
 Add a Carbon14 atom to the play area. What happens to that Carbon14 atom? ________________________________________________________________________________
 Do all Carbon14’s decay at the same time? ____________________________________________
 Add 50 Carbon14s. (click five times.) What happens? _______________________________________________
 and Using 20 Carbon14s, draw the pie graph at the following time periods:
5000 Years 
10000 years 
15000 years 



 Redo the above with 100 Carbon14 atoms and fill in the three boxes below.
5000 Years 
10000 years 
15000 years 



 How do the pie graphs of 20 atoms compare to those of 100 atoms? __________________________________________
 Generally, does the size of a radioactive sample affect halflife? __________ Why/Why not? _______________________
Consider Uranium238…
 Carbon14’s halflife was measured in thousands (5700) of years. About how long is Uranian238’s halflife? _________________________________________________________________________
 How many protons does U238 have? _____________ How many neutrons? __________________
 Into what atom does Uranium238 decay? ______________________________________________
 Does the size of the sample of Uranium238 affect its halflife? _______________________________________________
About that Unknown Element….
 How would you determine the halflife of this unknown element? Write up a little plan here:
 Estimate the halflife of this element. _________ seconds.
Observe the decay curves ( % remaining vs time) for Carbon14 and Uranium238. Sketch the decay curve for those isotopes here:
Determine how the little Geiger counter works in Measurement and Dating Game. Estimate the age of each of the following objects in the list below:
Item 
Estimated Age 
Item 
Estimated Age 












Analysis questions
 Why can’t we use Carbon14 to date the rocks? ___________________________________________________________
 Why couldn’t the fish fossil or dinosaur skull be dated with either C14 or U238? _________________________________
___________________________________________________________________________________________________
 Could Carbon14 be used to date a hammer suspected of being used in 3400BC? _________ __________Why/Why not? ___________________________________________________________________________________________________
 The halflife of the unknown element was about _______ seconds.
 Starting with 100 Carbon14 atoms, how many would you expect to have after one halflife? _____ After three? ______
 Make a small sketch of what a decay curve may look like for an unknown elementà
 You happen upon an antiques store and the clerk claims that he has a belt that was once worn by Alexander the Great, around 350 BC. You radiocarbon date it and find the percent of carbon to be 75% remaining. Could the belt be genuine?
How did you arrive at your answer?
Intro to HalfLife PhET Lab (Radioactive Dating Game).