In this activity we will use pennies to represent isotopes of the element "coinium". The element coinium is analogous to any element for which we find some unstable radioactive isotopes. Coinium, like other radioactive elements, has some isotopes which are unstable and will decay over time. Atoms decay into other atoms, smaller particles and energy, while coinium atoms decay from "heads" up to "tails" up. In this activity we will look at the rate of decay for the fictitious element coinium and track the stability of one representative atom.
Procedure:
1. Place 100 pennies "heads" up on a cafeteria tray. Use a small piece of masking tape to mark one of the pennies.
2. Place another cafeteria tray over the original and shake a number of times. Some of the coinium atoms should have decayed (flipped to tails). Record the number of atoms that decayed and remove them. Be sure and record when the marked atom decays.
3. Cover the original tray and flip the pennies. Again record and remove the decayed "atoms".
4. Continue flipping until all of the "atoms" have decayed.
5. Create a data table with the following headings; flip number, number of decayed atoms, and percentage of atoms remaining. Also mark with an asterisk the flip number when the marked penny decayed.
6. Construct a graph plotting flip number and percentage of atoms remaining.
7. Plot a line of best fits using an exponential relationship and answer the following questions.
- Questions -
1) How many flips would it take for 33 pennies to "decay"?
2) Scientists describe the stability of an isotope by reporting it's half-life. Half-life is the amount of time required for one half of a radioactive sample to decay. What is the "1/2 flip life" of your pennies?
3) How many pennies would you expect to remain after 7 flips?
4) How many flips would it take to have 1/8 as many pennies you started with?
The graph below shows the radioactive decay curve for the isotope thorium-234. Use the graph to answer these questions.
5) What percent of the isotope remains after 60 days?
6) How many grams of a 250-g sample of thorium-234 would remain after 40 days?
7) How may days would pass while 44 g of thorium-234 decayed to 4.4 g of thorium-234?
8) What is the half-life of thorium-234?