Ms. LovettHalf-life Lab

Earth History Dating Techniquespage 1

NAME:

Half-life Simulation Lab

Background and Information

Radioactive elements decay at a constant, measurable rate. The time it takes for a half of any given amount of original element to change into a new isotope or other element is called a “half-life”. You can demonstrate this concept with a simple candy model.

Pre-lab Questions

Match the terms with the definitions below. Write the letter of the correct phrase in the blank beside the question number.

_____ 1. Absolute Dating

_____ 2. Half-life

_____ 3. Radioactive Decay

_____ 4. Radiometric Dating

_____ 5. Relative Dating

_____ 6. Uniformitarianism

  1. Concept of determining the age using known ages of surrounding rock layers.
  2. Time it takes for half of the atoms in an isotope to decay.
  3. Breaking down of a neutron into a proton and an electron.
  4. Principle that Earth processes occurring today are similar to those that occurred in the past.
  5. Calculating the absolute age of any rock by measuring the amounts of parent and daughter material in the rock and knowing the half-life of the parent material.
  6. Process that uses the properties of atoms in rocks and other objects to determine age.

Materials

Clock with second hand.

32 candy pieces stamped with trademark letter

2 Cups

Paper towel

Tray

Research & Hypothesis

Each time you shake your candy and dump it into the tray – it is expected that half will be turned with the marked side up. This is representative of the “decayed” material.

The UNMARKED SIDE represents PARENT material; MARKED SIDES represent DAUGHTER products or broken down material.

Fill in the table below with your expected results.

amount of original left / Parent Material
Remaining after
Half-life occurred / Half-lifeduration
always
5 seconds / Total Time passed / Half expected to decay during this half-life / Parent Product
Left
(Parent minus decays) / Stored breakdown material (daughter)
previous stored + those that just decayed / Final Ratio of parent to decayed
100% / Start:32
No half life occurred yet / 5 sec. / 5 sec / 16
daughters created this time / 16 / 16 / 16:16
(1:1)
1/2 / 5 sec. / 10 sec / 8 / 24 / 8:24
(1:3)
1/4 / 8 / 5 sec. / 4 / 4:28
(1:7)
1/8 / 5 sec. / 2:30
(1:15)
1/16 / 1:31
1/32 / 1 / --

When your table is complete, let your teacher check it, and you are ready to begin.

Procedure

  1. Obtain your materials. You MAY NOT eat your candy until completion of lab and approval from teacher. Since you are working in groups, each of you will be allowed about 10 or 11 pieces at the end.
  1. Count your candy to be sure you have 32 pieces.
  1. Put one cup aside and keep it for break down product storage.
  1. Put all your candy into the cup and shake for 5 seconds; one person should shake the candy the other should watch the time. This shaking represents the half-life time going by.
  1. Spill your candy into your tray. Remove all pieces with the marked side up, placing them in the other dish for storage. These represent the amount of parent material that decayed – they are your “daughter product”.
  1. Begin to record your results in the table. Be sure to record the number of candy pieces removed, and the number remaining. DO NOT return removed candy to your cup! Keep it stored!
  2. Repeat steps 3-6 until there is either zero or one parent candy left. Be sure your table is complete.
  1. Use your graphing space below to make a line graph between the half-life and the amount of material left. X axis is time and Y axis is quantity of parent product remaining.

Analysis and Conclusions:

  1. In terms of radioactive decay, what does the unmarked side of the candy represent?
  1. What does the marked side of the candy represent?
  1. What is the half-life of your candy?

4. How many half-lives did it take for about half of your candy to decay?

5. Why is using this candy model useful for studying isotopes? Why is the type of candy selected important?

6. Using your graph below (identify these spots on your line graph) about how many candy pieces should be left after 12 seconds of decay? After 18 seconds?

Data Table

Parent Material
Remaining after
Half-life occurred / Half-life
duration
always
5 seconds / Total Time passed
(add 5 sec to previous time) / Amount Decayed during half life / Parent Product
Left
(Parent minus decays) / Stored breakdown material (daughter)
previous stored + those that just decayed
Start:32
No half life occurred yet / 5 seconds / 5 seconds / daughters created this time

Conclusions (Use a separate sheet of paper as needed)

  1. If Carbon-14 has a half life of 5730, how long will it take for 1000 kg sample to decay to 500 kg, 125 kg, and 15.6 kg? (SHOW WORK in a table)
  1. Some fossil bones contain 1/8 their original amount of Carbon-14. How many half-lives have passed? How old are the bones? (show work in a table)
  1. Suppose the radioactive isotope you are modeling has a half-life of 713 million years. How old is the sample if 1/32 of the original isotope remains? (Show Work in a table)