Half Life of M & Mium

Name______

Background: You should know the term “half-life” and know how it is related to radioactive

elements. The half-life of a radioactive element is the time it takes for half of its atoms to decay into something else. For example, iodine-125 (I-125) has a half-life of about 60 days; therefore, in 60 days, 1g of I-125 will turn into half a gram of iodine-125 and half a gram of something else (the radioactive decay products of radium). After another 60 days have elapsed, only a ¼ of the original 1g of I-125 will remain.

Purpose: To determine the half-life of the element M&Mium.

Materials:

SampleM&Mium Isotopes

**Radioactive members of this isotope family are easily distinguished via a bold m on

the front surface of the atom (parent isotope).**

1 cup

pencil/pen

white piece of paper

paper plates (parent, daughter)

1 sheet of graph paper

Clean hands!

Procedure:

  1. Label plates: parent, daughter
  2. Put the atoms on the plate. Count the number of M&Mium atoms (all of them). Have group members help count. Record the total number of radioactive atoms (all the m & ms) you start with, on the top of your data table. After you count all the atoms, place them in the cup.
  1. Cover and shake/rattle the cup.
  1. Carefully pour your atoms onto a plate. Gently shake the plate so that there is one layer of the atoms. You will see that several of the previouslyradioactive atoms in the group have decayed, and the m is no longer visible. (NOTE: You should not eat any of the decayed M&Mium atoms until after your 3rdtrial)
  1. Remove the daughter atoms (without m showing)-put them on the daughter plate. Count them and record the number in the column, Trial 1, round 1 on your data table.
  1. Put the parent atoms left on your plate back into cup and repeat steps 2-4. Each round, you will record the total number that has decayed in each trial. Record your data in the corresponding row for each round.
  1. Now you need to continue this pattern until no more radioactive members remain or until you get to round 9.
  2. Put all the atoms back into the cup and start the 2nd trial, repeat steps 2-5). Repeat for the 3rd trial.
  3. Calculate the average by adding each trial for each round together and dividing by 3.

Total M&Mium atoms at beginning=______

Round
(years) / Trial 1
Total #decayed
(keep a running total) / Trial 2
Total #decayed
(keep a running total) / Trial 3
Total #decayed
(keep a running total) / Average # of decayed atoms
(add trials 1-3, then divide by 3)

Analysis:

Using the graph paper provided, construct a graph of average number of decayed atoms (y axis) versus time (x axis). Remember to label yourx-axis, y-axis, and indicate a title for your graph. Each round/shake equals 1 year.

Questions:

1)If each shake represents 1 year, what is the half life of m & mium?

2)Which m&m represented the parent element?

3)Which m&m represented the daughter element?

4)How do scientists use half life to determine the age of rock?