INTRODUCTION TO RADIATION
Introduction:
This experiment is designed to allow you to use a nuclear scaler to collect some data for
three sealed sources. The scaler contains a Geiger-Muller tube (G-M tube) that detects
radiation emitted from atoms. After you have collected the data, you will analyze it to
determine what effects, if any, each variable has on the number of counts.
Purpose:
The purpose of this experiment is to collect data for three radioactive sources and
describe the effects of time, distance, and shielding.
Student Outcomes:
1. Use a scaler and G-M tube to collect data for radioactive sources.
2. Analyze data to describe the effects of time, distance, and shielding on the
number of counts per unit time.
Equipment/Materials:
sealed sources (alpha, beta, and gamma)
scaler and G-M tube
absorber set or samples of various materials
forceps
Safety:
 This experiment presents no unusual safety hazards. It is good technique to
handle all radioactive sources with forceps.
 Always wear goggles and an apron in the lab
Procedure:
Part I: TIME
1.
Plug in the scaler and press the POWER button if this has not already been done.
Press STOP and RESET to clear the display. Set the voltage at the value you
determined in an earlier lab or at the operating voltage printed on the G-M tube.
2.
Obtain a sealed alpha source, and place it on the second shelf of the sample holder.
Remember to use forceps when handling the sources.
3.
Set the timer to 0.5 minutes. Push the COUNT button, and record the value when
the STOP light goes on. Press the RESET button, set the timer to 1.0 min, and take
another reading. Repeat, taking a 2.0 minute reading.
4.
Repeat steps 2 & 3 for a beta source and a gamma source.
Part II - DISTANCE
1.
Place a sealed alpha source on the top shelf of the sample compartment, and take a
one minute reading. Lower the source to the next shelf, and take another one minute
reading. Remember to record your data and to reset the scaler between
measurements. Continue until readings are taken on all the shelves.
2.
Repeat the procedure in Step 1 with the beta and gamma sources. The order in
which they are used does not matter.
Part III - SHIELDING
1.
Take a one minute reading with no sample in the sample compartment. This will
serve as the background reading.
2.
Place a sealed alpha source on shelf 2. It will remain on this shelf for the entire
experiment. Take a one minute reading.
3.
Place the index card over the sealed source sample, and take another one minute
reading. Repeat the procedure with the other materials indicated on the data sheet.
4.
Repeat Step 2 and 3 for the beta and gamma sealed sources.
5.
Take another one minute background reading.
Data
Part I – TIME
ALPHA
BETA
GAMMA
________________________________________
________________________________________
________________________________________
0.5 minute count
1.0 minute count
2.0 minute count
Part II - DISTANCE
Alpha Source
Shelf 1
____________
Shelf 2 ____________
Shelf 3 ____________
Shelf 4 ____________
Shelf 5
____________
Shelf 6 ____________
Gamma Source
Shelf 1
____________
Shelf 2
____________
Shelf 3
____________
Shelf 4
____________
Shelf 5
____________
Shelf 6
____________
Beta Source
Shelf 1
____________
____________
____________
____________
Shelf 5
____________
Shelf 6
____________
Shelf 2
Shelf 3
Shelf 4
Part III - SHIELDING
Background
Alpha Source
Air
Paper
Al Foil
Al Metal
Lead
Other
______________
_____________
_____________
_____________
_____________
_____________
_____________
Beta Source
Air
Paper
Al Foil
Al Metal
Lead
Other
_____________
_____________
_____________
_____________
_____________
_____________
Gamma Source
Air
Paper
Al Foil
Al Metal
Lead
Other
_____________
_____________
_____________
_____________
_____________
_____________
_____________
Background
Questions:
1.
What were the three independent variables studied in this experiment?
2.
Describe the relationship you observed between count rate and time in Part I.
3.
a. Describe the relationship you observed between distance and count rate in part II.
b. What term is used to describe this relationship?.
4.
Were there any differences between the sealed sources in Part II? What does this tell
you about the ability of different forms of radiation to travel through air?
5.
What happened when the distance between the beta source and the detector doubled?
6.
How do you know if a shielding material has completely stopped a particular type of
radiation?
7.
From your data, what substance would be required to stop each of the three types of
radiation?
Teacher Notes
Introduction to Radiation
Standards Met:
3.4.12.A – Apply concepts about the structure and properties of matter.
 Apply the predictability of nuclear decay to estimate the age of materials that
contain radioactive isotopes.
 Explain how radioactive isotopes that are subject to decay can be used to estimate
the age of materials.
 Classify and describe, in equation form, types of chemical and nuclear reactions.
3.7.12.B – Evaluate appropriate instruments and apparatus to accurately measure
materials and processes.
 Apply and evaluate the use of appropriate instruments to accurately measure
scientific and technological phenomena within the error limits of the equipment.
3.1.12.C – Assess and apply patterns in science and technology.
 Assess and apply recurring patterns in natural and technological systems.
3.4.10.A – Explain concepts about the structure and properties of matter.
 Know that atoms are composed of even smaller sub-atomic structures whose
properties are measureable.
3.7.12.A – Apply advance tools, materials and techniques to answer complex questions.
 Evaluate and use technological resources to solve complex multistep problems.
Lab Time:
A total of two lab periods is probably required for data collection. The
time required can be shortened if counts are taken for a half-minute
instead of one minute. The class can also pool their data.
Preparations:
Time: This lab does not require the preparation of any solutions. You may wish
to turn the scalers on so they are warmed up when the students arrive. If absorber
kits are not available, any pieces of sheet metal or other materials can be used in
their place. Set up time should not take more than 10 minutes.
Sample Data/Results:
Data
Part I - TIME
0.5 minute count
1.0 minute count
2.0 minute count
___251________
___494________
___1002_______
Part II - DISTANCE
Alpha Source
Shelf 1
____1002______
Shelf 2 _____300______
Shelf 3 ______45______
Shelf 4 ______15______
Shelf 5
______15______
Shelf 6 ______15______
Beta Source
Shelf 1
_2006_______
_1707_______
__998_______
__853_______
Shelf 5
__511_______
Shelf 6
__398_______
Shelf 2
Shelf 3
Shelf 4
Gamma Source
Shelf 1
____3018____
Shelf 2
____2104____
Shelf 3
____1523____
Shelf 4
_____747____
Shelf 5
_____364____
Shelf 6
_____203____
Part III - SHIELDING
Background
Alpha Source
Air
Paper
Al Foil
Al Metal
Lead
Other
_________15__
_______1999__
_________16__
_________17__
_________15__
_________16__
_________15__
Beta Source
Air
Paper
Al Foil
Al Metal
Lead
Other
____2000_____
____2000_____
____2000_____
____1000_____
_____100_____
depends on substance
Gamma Source
Air
Paper
Al Foil
Al Metal
Lead
Other
____3000_____
____3000_____
____3000_____
____3000_____
____1600_____
few substances other than lead will
reduce count rate significantly
_______15____
Background
Answers to Questions:
1.
Time, distance, and shielding
2.
Count rate should increase as time increases (direct relationship).
3.
a. Count rate decreased as distance increased
b. Inverse relationship
4.
Yes. Alpha radiation drops off more quickly as the distance increases. Gamma and
beta travel through air more easily than alpha.
5.
The count rate should drop to one fourth of the original count rate.
6.
The count rate should drop to background. Because of background, the count rate
will never drop to zero.
7.
Alpha
- index card (or air if the distance is great enough)
Beta
- usually thicker Al or thin Pb
Gamma - several inches of lead may be required to completely stop the
gamma radiation
Evaluation
Introduction to Radiation
1.
Describe the effect of time on the count rate for a radioactive source.
2.
Which radioactive source was most easily affected by changes in distance? What
does this tell us about the ability of that type of radiation to travel through air?
3.
Which type of radiation required the least amount of shielding to stop it?
4.
Is it reasonable to expect the count levels to reach zero when using shielding? Why
or why not?
5.
Write a brief description which another student could use to measure count rates
using a scaler.
Answers to the Evaluation:
1. As time increases, the count rate increases. They are directly proportional.
2. Alpha particles are easily absorbed by air.
3. Alpha particles.
4. No, background radiation will always be present.
5. The discussion should include: turning on the equipment, allowing it to warm up,
setting the time, recording the values, using the reset button, and taking the next
count.
Considerations:
This lab could also be done utilizing the discovery approach. Ask students to discover
what effects time, distance, and shielding have on each type of radiation. Minimal
directions (how to set operating voltage and which buttons to push) should be given. This
approach may require more time.
No special preparation is required for this experiment. If absorber sets are not available,
any uniform pieces of material may be used. Sheet metal cut into 2 inch squares would
work well. (This is the time to remind the industrial arts teachers that they owe you
several favors.)
The distance part of this activity can be used as an inverse square activity. When the
distance is doubled, the count rate should be cut to one fourth. This works better for beta
sources and longer counting times.
Last updated 10-02