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Radiation Activity Instructions
Introduction
Of the types of radiation produced in nuclear decay reactions, the three most common are alpha particles (?), beta particles (?), and gamma rays (?). All of them are considered to be forms of ionizing radiation, that is, when they strike atoms or molecules in their paths they cause electrons to be knocked away, forming ions or free radicals. While this is generally not much of a concern with inanimate materials, these highly reactive species can cause undesirable effects in living tissue.
Alpha
particles are fast moving particles that contain two protons and two neutrons, which make them identical to helium nuclei, with a mass number of 4 and a charge of 2+. They are written using either the Greek letter ? or the symbol for the helium nucleus, He-4.
Beta
particles are high-energy electrons, with a mass number of 0 and a charge of 1–. They are identical to other electrons in the atom, but do not exist in the nucleus until a neutron decays into a proton and an electron. They are written with either the Greek letter ?.
Gamma
rays are high-energy photons (similar to X rays but higher energy). They are given the Greek letter ?.
Because cells in our bodies can be damaged by ionizing radiation, appropriate shielding must be used when working with radioactive sources. There are three ways to minimize your exposure to ionizing radiation when working with radioactive materials:
Use proper shielding. Since alpha particles are the heaviest of the forms of radiation and carry the greatest charge, they interact the most strongly with matter and are absorbed within a very short distance. A piece of paper, a lab coat, even the outer, dead layer of our skin are sufficient protection against alpha particles. (If inhaled or ingested, however, alpha particles can cause serious damage to internal organs.)
Beta particles, having a smaller mass and charge, are able to penetrate matter to a greater depth, as far as 4-
5 mm
into body tissue. While beta particles are absorbed before they can reach internal organs, they can be damaging to the skin. Heavy clothing and gloves, or metals such as aluminum, provide adequate protection from beta particles.
Gamma rays are the most penetrating of all, passing right through body tissue and many materials. They require much more dense materials such as lead or concrete to stop them.
Table 1 lists the approximate penetration depths for the types of radiation in various materials.
Table 1. Approximate Penetration Depths of Radiation in Various Materials
AlphaBetaGamma
Body Tissue
0.05 mm
5 mm
>50
0 mm
Aluminum
0 mm
2 mm
300 mm
Lead
0 mm
0.4 mm
300 mm
(2) Minimize the time you spend exposed to radioactive materials. If you are in an area with radioactive sources for twice as long, you will get twice as much exposure.
(3) Keep your distance. This is the relationship we will examine in part 3 of this laboratory exercise.
We often see reports of archaeological studies that claim to have found a scroll from the time of the Romans, a mummy from 1000 B.C., or a piece of bone from a human that is 10,000 years old. How do we determine the ages of these objects? One method is to use a form of radiological dating that relies on the decay of carbon-14, a beta emitter.
Carbon-14 is created in the upper atmosphere, which is constantly being bombarded by cosmic rays of very high energy. These rays consist of electrons, neutrons, and atomic nuclei. One of the important reactions is the capture of a neutron by 14N to create 14C and a proton:
The 14C reacts with oxygen in the atmosphere to form carbon dioxide, which eventually makes its way into the biosphere where it is taken up by plants during photosynthesis. Animals eat the plants—and we eat both animals and plants—ultimately exhaling the 14C again as CO2. In this way a steady concentration of 14C is maintained in living tissue. (Although 14C emits ionizing radiation, and can therefore damage cells, the natural abundance of 14C is very small: there exists only one atom of 14C in every 1012 atoms of carbon.)
Once an organism dies the 14C is no longer replenished, and the amount of 14C steadily decreases as it undergoes ? decay. Thus when a sample of that scroll, the mummy, or the bone is measured for its 14C content, there is less of it than in a living organism. If we assume that the person who was mummified had the same amount of 14C in her tissues when she was alive as we do today, and we know the rate at which 14C decays, we can determine her age.
The half-life of a radioisotope is the time it takes for one-half of a sample to decay. Carbon-14 has a half-life of 5730 years, which means that after that period of time, only half of the 14C that was originally present in an organism would remain. After another 5730 years, only half of that quantity would be present, or one-quarter would remain, and so on.
Similarly, the radioactivity of a sample (as measured by a Geiger counter) will decrease by the same fraction. Note that if a sample is either too young or too old, this method will not work. If a piece of bone is only a couple years old, there will have been too little decay of 14C for us to be able to measure a decrease. Likewise, if it is more than about 40,000 years old, there will be too little 14C left to measure accurately.
Objectives
In this experiment, you will
Estimate the age of various samples using radiocarbon dating.
Procedure
Part 1. Types of Radiation
Part 2. Shielding and Gamma Rays
Part 3. Radiation Intensity vs. Distance
Part 4. Radiocarbon Dating
To determine the age of the sample:Open the link on the screen (http://www.uccs.edu/vgcl/nuclear-chemistry/experiment-5-radiocarbon-dating.html) titled “Worksheet” located directly above the drop-down list of samples.ALL YOU NEED TO DO TO THIS WORKSHEET IS TYPE VALUES INTO THE “Initial Activity:” box above the graph titled Decay Curve for Carbon-14 and interpret the graph. Ignore the rest of the worksheet.For one of the present-day materials, type its activity in the “Initial Activity” cell and hit Enter. This will generate a decay curve for 14C based on that starting activity.For each of the archaeological objects made of that material, estimate its age using the activity and the 14C decay curve. Enter the age into your data table in evernote.Repeat steps c and d for the other present-day materials. RADIATION ACTIVITY DATA SHEET
PRE-LAB QUESTIONS
1. When ionizing radiation strike atoms or molecules in their paths they cause electrons to be
knocked away, forming ________________________________________________.
2. Use Table 1 and the information in the introduction to answer the following:
a. What kinds of materials would provide sufficient protection for a person working
with alpha-emitting sources?
b. What kinds of materials would provide sufficient protection for a person working
with beta-emitting sources?
c. What do you suppose you would need to do to protect yourself from gamma
radiation?
3. True or False, a steady concentration of 14C is maintained in living tissue and decreases once
an organism dies.
DATA
Part 1. Types of Radiation
Activity (counts/sec)
source
Use /
application
No
shielding
Paper
1 mm
Cardboard
Fe-59
Ga-67
I-125
P-32
Ra-222
Sr-85
Part 2. Shielding and Gamma Rays
Source: Gamma Rays (strontium-85)
Activity (counts/sec)
Thickness
(mm)
None
1
2
3
4
Cardboard
Aluminum
Lead
1 mm
Aluminum
1 mm
Lead
Type of
Radiation
Part 3. Radiation Intensity vs. Distance
Source: Gamma Rays (gallium-67)
distance
(cm)
Activity
(counts/sec)
Part 4. Radiocarbon Dating
source
Activity
(counts/sec)
Age
(yrs)
Present-day materials
1
wood
0
2
paper
0
3
bone
0
4
5
6
7
8
9
10
Archaeological objects
Bone, Bering land
bridge
Wood, tomb of
pharaoh Zoser
Bone, La Brea tar
pits
Paper, Dead Sea
scrolls
Skull, Laguna
Beach, CA
Wooden timber,
Stonehenge
Bone, Pedra
Furada, Brazil
Wooden beam,
India
DATA ANALYSIS QUESTIONS
1. As mentioned in the introduction, X-rays are similar to gamma rays. Why is a lead apron
placed over a patient’s chest and lap when receiving routine X-rays in the dentist’s office?
2. X-rays are a type of ionizing radiation similar to gamma rays. Why does the X-ray technician
leave the room when you receive an X-ray?
3. Use your age data from Part 4 to determine the year of the following (Include A.D. or B.C.)
a. The year the paper was made for the Dead Sea scrolls. (Does this year make sense
with the history of the Dead Sea scrolls?)
b. The year the person died whose bone was discovered in Pedra Furada, Brazil.
RADIATION ACTIVITY INSTRUCTIONS
INTRODUCTION
Of the types of radiation produced in nuclear decay reactions, the three most common are
alpha particles (α), beta particles (β), and gamma rays (γ). All of them are considered to be forms
of ionizing radiation, that is, when they strike atoms or molecules in their paths they cause
electrons to be knocked away, forming ions or free radicals. While this is generally not much of a
concern with inanimate materials, these highly reactive species can cause undesirable effects in
living tissue.
Alpha particles are fast moving particles that contain two protons and two neutrons, which
make them identical to helium nuclei, with a mass number of 4 and a charge of 2+. They are
written using either the Greek letter α or the symbol for the helium nucleus, He-4.
Beta particles are high-energy electrons, with a mass number of 0 and a charge of 1–. They
are identical to other electrons in the atom, but do not exist in the nucleus until a neutron decays
into a proton and an electron. They are written with either the Greek letter β.
Gamma rays are high-energy photons (similar to X rays but higher energy). They are given the
Greek letter γ.
Because cells in our bodies can be damaged by ionizing radiation, appropriate shielding
must be used when working with radioactive sources. There are three ways to minimize your
exposure to ionizing radiation when working with radioactive materials:
(1) Use proper shielding. Since alpha particles are the heaviest of the forms of radiation and
carry the greatest charge, they interact the most strongly with matter and are absorbed
within a very short distance. A piece of paper, a lab coat, even the outer, dead layer of
our skin are sufficient protection against alpha particles. (If inhaled or ingested, however,
alpha particles can cause serious damage to internal organs.)
Beta particles, having a smaller mass and charge, are able to penetrate matter to a greater
depth, as far as 4-5 mm into body tissue. While beta particles are absorbed before they
can reach internal organs, they can be damaging to the skin. Heavy clothing and gloves,
or metals such as aluminum, provide adequate protection from beta particles.
Gamma rays are the most penetrating of all, passing right through body tissue and many
materials. They require much more dense materials such as lead or concrete to stop them.
Table 1 lists the approximate penetration depths for the types of radiation in various
materials.
Table 1. Approximate Penetration Depths of Radiation in Various Materials
Alpha
Beta
Gamma
Body Tissue
Aluminum
Lead
0.05 mm
0 mm
0 mm
5 mm
2 mm
0.4 mm
>500 mm
300 mm
300 mm
(2) Minimize the time you spend exposed to radioactive materials. If you are in an area
with radioactive sources for twice as long, you will get twice as much exposure.
(3) Keep your distance. This is the relationship we will examine in part 3 of this laboratory
exercise.
We often see reports of archaeological studies that claim to have found a scroll from the time
of the Romans, a mummy from 1000 B.C., or a piece of bone from a human that is 10,000 years
old. How do we determine the ages of these objects? One method is to use a form of radiological
dating that relies on the decay of carbon-14, a beta emitter.
14
6C
→ 147N +
0
−1𝑒
Carbon-14 is created in the upper atmosphere, which is constantly being bombarded by
cosmic rays of very high energy. These rays consist of electrons, neutrons, and atomic nuclei. One
of the important reactions is the capture of a neutron by 14N to create 14C and a proton:
1
0n
+
14
7N
→
14
6C
+ 11H
The 14C reacts with oxygen in the atmosphere to form carbon dioxide, which eventually makes
its way into the biosphere where it is taken up by plants during photosynthesis. Animals eat the
plants—and we eat both animals and plants—ultimately exhaling the 14C again as CO2. In this way
a steady concentration of 14C is maintained in living tissue. (Although 14C emits ionizing radiation,
and can therefore damage cells, the natural abundance of 14C is very small: there exists only one
atom of 14C in every 1012 atoms of carbon.)
Once an organism dies the 14C is no longer replenished, and the amount of 14C steadily
decreases as it undergoes β decay. Thus when a sample of that scroll, the mummy, or the bone
is measured for its 14C content, there is less of it than in a living organism. If we assume that the
person who was mummified had the same amount of 14C in her tissues when she was alive as we
do today, and we know the rate at which 14C decays, we can determine her age.
The half-life of a radioisotope is the time it takes for one-half of a sample to decay. Carbon14 has a half-life of 5730 years, which means that after that period of time, only half of the 14C
that was originally present in an organism would remain. After another 5730 years, only half of
that quantity would be present, or one-quarter would remain, and so on.
Similarly, the radioactivity of a sample (as measured by a Geiger counter) will decrease by the
same fraction. Note that if a sample is either too young or too old, this method will not work. If a
piece of bone is only a couple years old, there will have been too little decay of 14C for us to be
able to measure a decrease. Likewise, if it is more than about 40,000 years old, there will be too
little 14C left to measure accurately.
OBJECTIVES
In this experiment, you will
• Identify the type of radiation produced by various nuclides by examining how much that
radiation penetrates shielding materials
• Examine the effectiveness of shielding against gamma rays by three materials.
• Estimate the age of various samples using radiocarbon dating.
PROCEDURE
Part 1. Types of Radiation
1. On your computer, go to: http://www.uccs.edu/vgcl/nuclear-chemistry/experiment-2types-of-radiation.html
2. Click on the apparatus to start the lab. The experimental setup includes a number of
radioactive sources, different types of shielding, and the apparatus to measure the
radioactivity. On the right is a Geiger counter that will measure radiation in counts per
second. On the left is a holder for the radioactive source, and in the middle is a holder for
the shielding material.
3. Click on the drop-down list of radioactive sources and choose a nuclide. Drag the source
into the sample holder. Record the name of the source and uses/applications of this nuclide.
4. Click on the Geiger counter switch to turn it on. Record the activity of the sample in
counts/sec. (The needle on the gauge may move around a bit. You should try to get an
average reading. Note that the scale on the gauge is not linear.)
5. Click the switch again to turn it off.
6. Click on the drop-down list of shielding materials and choose one. Drag the shielding into
its holder in the apparatus. Again click on the Geiger counter switch, and again record the
activity in the appropriate column in the worksheet.
7. Repeat step 7 for the other types of shielding material.
8. Repeat steps 3-7 for all of the radioactive sources.
9. Use table 1 to identify the type of radiation (alpha, beta, or gamma) given off by each
nuclide.
Part 2. Shielding and Gamma Rays
1. On your computer, go to: http://www.uccs.edu/vgcl/nuclear-chemistry/experiment-3shielding.html
2. Click on the apparatus to start the lab. The experimental setup includes a number of
radioactive sources, several 1-mm thick sheets of three different types of shielding, and the
apparatus to measure the radioactivity.
3. Click on the drop-down list of radioactive sources and choose strontium-85, a gamma
emitter. Drag the source into the sample holder. Click on the Geiger counter switch to turn
it on. Record the activity of the sample in counts/sec. Click the switch again to turn it off.
4. Click on the drop-down list of shielding materials and choose a single sheet (1 mm) of one
of them. Drag the shielding into its holder in the apparatus. Again click on the Geiger
counter switch, and again record the activity in the appropriate column in the worksheet.
5. Repeat step 4 for the other types of shielding materials and thicknesses.
Part 3. Radiation Intensity vs. Distance
1. On your computer, go to: http://www.uccs.edu/vgcl/nuclear-chemistry/experiment-4radiation-and-distance.html
2. Click on the apparatus to start the lab. The experimental setup includes the radioactive
source (gallium-67, a gamma emitter), a ruler to measure the distance from the source to
the detector, and the apparatus to measure the radioactivity. Click on the drop-down list to
retrieve the source and drag the source into the sample holder.
3. Click on the 1-cm mark on the ruler to position the source holder at 1 cm distance from the
detector. Click on the Geiger counter switch to turn it on. Record the activity of the sample
in counts/sec. Click the switch again to turn it off.
4. Click at a point on the ruler to move the source and record the activity for all distances in
the data table.
Part 4. Radiocarbon Dating
1. On your computer, go to: http://www.uccs.edu/vgcl/nuclear-chemistry/experiment-5radiocarbon-dating.html
2. Click on the apparatus to start the lab. The experimental setup includes a number of
samples of 14C isolated from objects discovered in archaeological excavations, and the
apparatus to measure the radioactivity.
3. Click on the drop-down list of samples and choose one. Drag the source into the sample
holder. Click on the Geiger counter switch to turn it on. Record the activity of the sample in
counts/sec. Click the switch again to turn it off.
4. Repeat step 3 for the other samples.
5. To determine the age of the sample:
a. Open the link on the screen (http://www.uccs.edu/vgcl/nuclearchemistry/experiment-5-radiocarbon-dating.html) titled “Worksheet” located
directly above the drop-down list of samples.
b. ALL YOU NEED TO DO TO THIS WORKSHEET IS TYPE VALUES INTO THE “Initial
Activity:” box above the graph titled Decay Curve for Carbon-14 and interpret the
graph. Ignore the rest of the worksheet.
c. For one of the present-day materials, type its activity in the “Initial Activity” cell and
hit Enter. This will generate a decay curve for 14C based on that starting activity.
d. For each of the archaeological objects made of that material, estimate its age using
the activity and the 14C decay curve. Enter the age into your data table in evernote.
e. Repeat steps c and d for the other present-day materials.
