Chemistry Lab

Name: ______________________________

Date: ______________________________

CHM 101L Module Eight Lab Activity: Nuclear Decay of Candium

Overview: In this investigation, you will simulate nuclear decay, record and graph your data, and observe the nature of exponential decay.

Safety:

Read all the instructions for this laboratory activity before beginning. Observe established laboratory safety practices.

Time Requirements:

Preparation: 5 minutes

Activity 1: 45 minutes

Materials needed but not supplied in the lab kit:

50 plain M&M™ candies

Computer with spreadsheet software

Plastic cup

Paper or notepad

Pencil

Preparation:

1) Obtain 50 M&M™ candies.

2) Place the 50 M&M™ candies in the plastic cup.

Activity 1:

1) Place one hand near the bottom of the cup and one hand over the top of the cup (covering the opening).

2) Carefully shake the cup for 10 seconds, keeping your hand over the top of the cup, preventing the candium atoms (candy) from escaping.

3) Gently pour out the candium atoms and count the number of pieces with the print side up. This is the number of decayed atoms.

4) Record your data in Table 1.

5) Return only the candium atoms that landed with the print side down (the remaining radioactive atoms) to the plastic cup.

6) Repeat this procedure 5 more times, representing a total of 6 half-lives, or until all of the radioactive atoms have decayed, which ever comes first.

7) Calculate the fraction of:

a. Fraction of parent atoms (radioactive isotopes) using the number of undecayed radioactive atoms divided by the initial number of radioactive candium atoms (50).

b. Fraction of daughter atoms (decayed isotopes) using the number of decayed atoms divided by the initial number of radioactive candium atoms (50).

c. Simplify these fractions if you can (e.g. 25/50 = 1/2).

8) Create a graph of your data using the half-life as your x-axis (horizontal line) and the number of atoms (both parent (radioactive) and daughter (decayed)) as your y-axis (vertical). This will produce a graph with two exponential curves, one showing a) the nuclear decay of candium and the other showing b) the production of daughter atoms over 6 half-lives.

Table 1

Half-life	# of Undecayed Candium Atoms (Parent atoms)	Fraction of Parent atoms (# parent atoms/50)	# of Decayed Candium Atoms (Daughter atoms)	Fraction of Daughter atoms (# daughter atoms/50)
0	50	50/50	0	0/50
1
2
3
4
5
6

*This lab was adapted from The Science House’s Radioactive Decay of Candium – Experiment 27.

Graph:

Insert your graph here.

Lab Questions:

1) Explain what a half-life is.

2) At the end of two half-lives, what fraction of the atoms had not decayed?

3) There are three types of radiation discussed in the Reactions and Changes – Nuclear Chemistry: An Introduction article. What are they and how does each type of radiation result in nuclear changes?

4) Radon is a naturally occuring radioactive gas that comes from the radioactive decay (transmutation) of uranium and it is found in certain soils. Because it is heavier than air, it tends to build up in the lower levels of households, like basements. Radon and its decay products can pose serious health hazards to people that are exposed to them. When radon-222 undergoes alpha decay, it transmutates into what daughter nucleus?

5) Some fossil bones containing 1/32 of their original amount of carbon-14 are found. How many half-lives have passed? How old are the bones?

(HINT: The half-life of carbon-14 is 5,730 years. If 1/8 of the original amount of carbon-14 was present, 1/8 = 1/23 or 1/(2x2x2), therefore 3 half-lives would have passed and therefore, the bones would be 5,730 years x 3 = 17,190 years old)

6) A 15 g sample of iodine-131 is giving off β radiation. The amount of iodine that remains is measured every day at 12:00 pm and recorded in a table used to produce the graph below. Using the graph below, locate the spot where the original amount (15 g) has dropped to half of its original value. How many days is this? (This is the half-life)

Iodine-131 (I-131)

I-131 (g) 0 1 2 3 4 5 6 7 8 9 10 11 12 15 13.8 12.6 11.55 10.65 9.75 9 8.25 7.5 6.9 6.3 5.85 5.4

Days

I-131 (g)