Contributed by: Council of Chief State School Officers (CCSSO)
Description:
The objective of the event is to help students understand radioactive
decay and be able to relate it to the concept of halflife.
The students are given 100 green beads that represent radioactive
atoms and 100 white beads that represent stable, nonradioactive
daughter atoms. The green beads are placed in one cup and the white
beads in another. They are asked to do two trials, one sampling
8 beads at a time and the other sampling 4 beads at a time. The
number of green beads removed in each sample should be recorded
and replaced with an equal number of white beads. Any white beads
removed in a sampling event should be returned to the cup that originally
began with all green beads. Once 50 green beads are removed from
the cup the elapsed time should be recorded.
Students graph each of the samples to show the relationship between
the number of green beads remaining in the cup on the yaxis and
the sample on the xaxis. The graphs represent the decay curves
for the samples.
Given some basic information, students are asked to explain how
many years they would have to be concerned about the radioactivity
of the sample and how they would dispose of the material.
A good response will show the student understands the concept
of halflife and can use this concept to determine when their sample
will be "safe". From the experiment they may also note that sampling
8 beads at a time will become safer in less time than when they
sampled 4 beads at a time because it has a shorter halflife. A
method of disposal must include limiting exposure of the radioactive
material to the environment.
Students will be working groups (23) while running the simulation
and collecting the data. Students should work alone while responding
to the questions.
This task is designed to take students approximately 4050 minutes
to complete.
General Instructions to the Teacher:
 Students need to be ready to work as soon as the period begins.
 Group assignments should be made in advance.
 The materials should be set out at each lab station, if possible.
 A central supply area, if needed, should be easily accessible.
 The supply area should have any supplies necessary for the experiment/simulation.
 All supplies should be clearly labeled.
Overall Task Content Area:

 Physical Science
Specific Knowledge Areas:

 Structure of atoms/Radioactivity
Performance Expectations:
 conducting investigations
 gathering, organizing, and representing data
 formulating conclusions from investigational data
 applying scientific principles to develop explanations and solve
new problems
National Science Education Standards:
12 B PS 1: Structure of atoms: Grades 912
1.4 Radioactive isotopes are unstable and undergo spontaneous
nuclear reactions, emitting particles and/or wavelike radiation.
The decay of any one nucleus cannot be predicted, but a large group
of identical nuclei decay at a predictable rate. This predictability
can be used to estimate the age of materials that contain radioactive
isotopes.
12 A SI 1: Ability to do scientific inquiry: Grades
912
1.4 Formulate and revise scientific explanations and models
using logic and evidence. Student inquiries should culminate in
formulating an explanation or model. Models should be physical,
conceptual, and mathematical. In the process of answering the questions,
the students should engage in discussions and arguments that result
in the revision of their explanations. These discussions should
be based on scientific knowledge, the use of logic, and evidence
from their investigation.
12 F SPSP 5: Natural and humaninduced hazards:
Grades 912
5.2 Human activities can enhance potential for hazards. Acquisition
of resources, urban growth, and waste disposal can accelerate rates
of natural change.
(Use the "hot" link on the PALS home page
to check the full text of related National Science Education Standards,
if desired.)
National Council of Teachers of Mathematics:
AL1: Understand patterns, relations and functions:
Grades 912 k. analyze functions of one variable by investigating
rates of change, intercepts, zeros, asymptotes, and local and global
behavior
AL3: Use mathematical models to represent and understand
quantitative relationships:
Grades 912 f. draw reasonable conclusions about a situation
being modeled
AL4: Analyze change in various contexts:
Grades 912 f. approximate and interpret
rates of change from graphical and numerical data
DAP2: Select and use appropriate
statistical methods to analyze data:
Grades 912 g. for univariate measurement
data, be able to display the distribution, describe its shape, and
select and calculate summary statistics
DAP3: Develop and evaluate
inferences and predictions that are based on data:
Grades 912 f. use simulations to explore
the variability of sample statistics form a known population and
to construct sampling distributions
CNX3: Recognize and apply mathematics in
contexts outside of mathematics:
Grades 912
REP3: Use representations to model and interpret
physical, social, and mathematical phenomena:
Grades 912
Materials:
At this station students should have:

 3 cups
100 green beads
100 white beads
clock with second hand or digital watch
2 colored pencils (different colors) for graphing
pen or pencil
Advance Preparation:
The teacher will need to do no special prep work prior to the
students performing this event.
Safety:
 Be careful.
 Teachers and students should always exercise appropriate safety
precautions and utilize appropriate laboratory safety procedures
and equipment when working on science performance tasks.
