Name: Shanna Shaked
Date:__Nov. 14, 2012__
MAT SIOP Lesson Plan: Radioactivity
I. Context:
Grade Level: Students are in Grade 11 or 12.
Discipline(s): This lesson is part of a course in Physics.
Unit Theme: This is part of the Nuclear Physics section of the Modern Physics unit.
Text(s) Used: The students can choose one of three different scientists to read about,
starting with the texts below. These were assigned as homework in a previous lesson.
Printouts were given to students without internet access.
 This is a moving story about Marie Curie’s life and discovery of Radium:
http://www.aip.org/history/curie/brief/03_radium/radium_1.html
 This is a description of Becquerel’s discovery in the form of a newspaper article:
http://www.earthmagazine.org/article/benchmarks-henri-becquerel-discoversradioactivity-february-26-1896. And this site contains translations of Becquerel’s
original publications:
http://web.lemoyne.edu/~giunta/ea/BECQUERELann.HTML
 This is a description of Rutherford’s contribution to the discovery of
radioactivity:
http://chemed.chem.purdue.edu/genchem/history/radioactivity.html.
*Connection to Wider Contexts:
Radioactivity is a concept that touches on the health of individuals, on the piecing
together of history, and on the ever-increasing topic of alternative sources of energy. It also
has a moving history that highlights the contributions of multiple scientists, including Marie
Curie, who broke many gender barriers in the scientific world.
Students will learn the roles that radioactivity plays in their own lives, while further
developing scientific literacy (called the Nature of Science) and inquiry skills. Students will
connect radioactivity to their own lives by measuring their individual exposure, by examining
carbon dating, and by looking at its connection to nuclear power. Students will better
understand the nature of science by examining the history of how scientists discovered
radioactivity. The story of Becquerel’s discovery of radioactivity shows how science can be
planned and predictions are made, but it also needs creative approaches to explain
observations. Finally, students will use inquiry to identify properties of beta radiation in a
manner similar to that done by scientists.
In making these various connections, this lesson connects to the content standards
involving radioactive isotopes, while also touching on standards regarding the atomic nature
of matter and atomic composition. This lesson connects to the broader theme in physics that
energy can be converted among different forms.
Student Population: There are 30 students in this class.
The class is composed of students with a wide variety of interests and ability levels.
Their math abilities range from trigonometry (five students) to calculus (five students). Five
students learn well from lecture, while ten prefer reading texts, and fifteen generally prefer
working in groups. About fifteen students are adept with and enjoy computer simulations,
while ten are more tactile and prefer manipulating objects. Five prefer just reading, writing
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and calculating. There are a few English Language Learners who find new physics
vocabulary particularly challenging.
II. State / National Standards:
 National Science Education Standards
o 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.
o Matter is made of minute particles called atoms, and atoms are composed of
even smaller components. These components have measurable properties,
such as mass and electrical charge. Each atom has a positively charged
nucleus surrounded by negatively charged electrons.
o The atom’s nucleus is composed of protons and neutrons, which are much
more massive than electrons. The nuclear forces that hold the nucleus of an
atom together, at nuclear distances, are usually stronger than the electric
forces that would make it fly apart.
III. Lesson Information
Lesson Title: Radioactivity: It’s not just for mutants.
Grouping Configurations:
Students will share their review of atom components in the pairs that they are already
seated in. This will ensure that students remember the relative masses and charges of the
parts of an atom and will encourage the students to communicate their creative depictions.
Students will also work in groups of three to piece together the history of
radioactivity based on each studying a certain scientist.
Short Range Learning Objectives & Assessments:
All numbers correspond to one another (numbers in content objectives, language
objectives and associated assessments all refer to the same set of activities). Note that the full
lesson spans three days, so I list objectives for all three days, but underline those that will be
addressed on the first day. The Lesson Procedures only describe the first day.
*Content (& Sociocultural Identity
Content Assessment:
Support) Objective(s):
1. Activity has students rank masses and
By the end of this lesson, my students will
electrical charges of an atom’s nucleus.
understand the different types of
Teacher circulates to ensure that all
radioactivity and its connection to the real
students are doing this correctly.
world. They will be able to say the following: 2. Students will hand in group activity on
1. I can identify the masses and electrical
history of radioactivity.
charges of an atom’s nucleus – proton,
3. In-class assignment has students identify
neutron, and electron.
what beta radiation is and where it comes
2. I can creatively explain how scientists
from.
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discovered and identified the properties
of beta radiation.
I can identify properties of beta
radiation.
I can use the concept of a half-life to
predict decay patterns.
I can compare and contrast the different
characteristics of alpha, beta and gamma
radiation.
I can estimate my own radiation
exposure. I can compare this to other
types of radiation exposure that I
measure in class.
I can research and describe real-life
applications of each type of radioactivity.
4. In-class assignment has students use the
concept of half-life to predict
populations over time.
5. Homework has students compare and
contrast properties of alpha, beta and
gamma radiation.
6. Homework has students use an online
calculator to estimate their own radiation
exposure. In class, students measure
radioactivity from various sources.
7. Homework has students research and
write about a real-life application of
radioactivity (carbon dating, nuclear
power, and everday exposure), and then
share and discuss these in class.
*Language Objective(s) for Integrated
Language Learning: The students will be
able to make the following statements by the
end of this lesson.
1. I will read and take notes about my
scientist to learn about the process of
science.
2. I will speak and listen to my group
members, so that we can piece together
the history of radioactivity. We will
collaboratively and creatively write or
draw a summary of this history.
3. I will learn vocabulary related to
radioactivity mechanisms by using my
textbook, my peers, the context of the
word, and my teacher.
4. I will learn vocabulary related to halflives in the same manner as #3.
5. I will clearly and concisely list
comparisons among the different types
of radiation.
6. I will demonstrate my comfort with the
internet, using the internet to estimate
my radiation exposure, and posting the
answer on our class website.
7. I will use the internet and other
resources to research and write about a
real-life application of radioactivity. I will
then speak about these with group
members in class.
Language Assessment: I, the teacher, will
use the following methods for assessing
these language skills.
1. I will check the notes of the student
when they are discussing scientist in
groups.
2. I will listen to the students working in
groups to ensure they are speaking and
listening. If a student is quiet, I will ask a
few questions.
3. There will be a short vocab quiz on
radioactivity as a warm-up on the second
day of the lesson plan. Peers will grade in
class.
4. There will be a short vocab quiz on halflives as a warm-upon the third day of the
lesson plan. Peers will grade in class.
5. The students will hand in their
comparisons of different radiation types.
Peers will grade in class.
6. Peers will post their estimated radiation
exposure online.
7. I will listen to the students as they
discuss radioactivity exposure in class.
3.
4.
5.
6.
7.
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Materials for Clarifying & Reinforcing:
text.
Visual Resources: Computer, projector and internet are used to show images and
Verbal / Written Resources: Students have read texts in preparation for class, and
will write in response to various activities.
Aural Resources: The students will interact with one another and thus practice aural
processing. And for the half-life activity, the sound of the M&Ms shaking in the Tupperware
will help draw the attention of aural learners.
Kinesthetic Resources: The shaking of the M&Ms provides some movement in the
class, especially since I will have the more kinesthetic learners contribute to shaking and
counting.
Tactile Resources: The warm-up provides an option for tactile learners (cut-outs of
the proton, neutron and electron) and allows the teacher to scaffold where needed.
Means to Lower the Affective Filter: I encourage students to share their work in
the context of the objectives we are all aiming for together. Also, each student will feel
valuable and knowledgeable, because they have information on their scientist that the other
group members need for the assignment.
Activity ideas were taken from some of the following resources (as well as those as
marked in the lesson):
 Phet Activities
o http://phet.colorado.edu/en/contributions/view/3559
 Layered activities
o http://www.help4teachers.com/KarenNuclearChemistry.htm
o http://www.help4teachers.com/GrantAtom.htm
IV. Lesson Procedures:
Before lesson

Write the following on the board:


Please hand in your homework notes in the homework folder!
Agenda:
 Monday, November 5, 2012 (spell everything out)
 Main Objective: Learn about radioactivity and beta decay
 Warm-up: Review parts of atom
 Groups: Explain how scientists discovered radioactivity
 Beta Radiation
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Exit slip: Two questions on radioactivity or real-world
applications
 HW: Half-life worksheet
Warm up: Write or draw what you think of when you think of
radioactivity.



Project, draw or print and post the image below to trigger some connections to
radioactivity:

A. Introduction of the Lesson / Hook:
1. Connection to / Activation of Funds of Knowledge
(Sociocultural Identity Support): (3 minutes)
“Good morning class! Today we’re going to learn about radioactivity! I think you’ve all heard
this word before, so before we launch into it, I want you to all write or draw what you think
of when you think of radioactivity. In terms of the science, real-world applications, or even
Spiderman. You have two minutes to write things down, and then I’ll call on some of you to
share your ideas.”
“If you haven’t yet handed in your homework notes, do that quickly now.”
Circulate and make sure students are participating. To encourage shy students to speak in
front of a group, look around for shy students that have written interesting points, and plan
to call on them.
Also collect the homework notes and divide these into groups based on the list I’ve
provided.
Take about a minute to hear and write the ideas of the students on the board to help
students feel validated and to connect these ideas to the concepts throughout the lesson.
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“Radioactivity is something that can be dangerous, that can provide energy, that tells us
how old things are, and that can help us be healthier, and Marie Curie won TWO Nobel
Prizes for her work on this topic.”
By listing a variety of real-world connections, this gets a variety of students excited to find
out more, and it offers an example of a (very) successful woman scientist.
2. Link Past Learning to Present Knowledge: (5 minutes)
“So we are going to talk about radioactivity today and tomorrow. More specifically, here is
what you’ll be able to say when we are done with this lesson: Today we will focus on the
bold objectives.” Show slide with the following:
1.
2.
3.
4.
5.
6.
7.
CONTENT OBJECTIVES
LANGUAGE OBJECTIVES
I can identify the masses and
1. I will read and take notes about my
electrical charges of an atom’s
scientist to learn about the process of
nucleus – proton, neutron, and
science.
electron.
2. I will speak and listen to my group
I can creatively explain how scientists
members, so that we can piece
discovered and identified the
together the history of radioactivity.
properties of beta radiation.
We will collaboratively and creatively
I can identify properties of beta
write or draw a summary of this
radiation.
history.
I can use the concept of a half-life to
3. I will learn vocabulary related to
predict decay patterns.
radioactivity mechanisms by using
I can compare and contrast the different
my textbook, my peers, the context of
characteristics of alpha, beta and gamma
the word, and my teacher.
radiation.
4. I will learn vocabulary related to halfI can estimate my own radiation
lives in the same manner as #3.
exposure! I can compare this to other
5. I will clearly and concisely list
types of radiation exposure that I
comparisons among the different types
measure in class.
of radiation.
I can research and describe real-life
6. I will demonstrate my comfort with the
applications of each type of radioactivity.
internet, using the internet to estimate
my radiation exposure, and posting the
answer on our class website.
7. I will use the internet and other
resources to research and write about a
real-life application of radioactivity. I will
then speak about these with group
members in class.
“I’m handing out a copy of this table. As we go through the lesson, I’m going to be
circulating , watching and listening. When I see that you’ve achieved a certain objective, I’ll
initial it. As the lesson continues, make sure that I’ve come around and seen all the things
you’ve learned to do today.”
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“To understand radioactivity, we need to remember what an atom is made up of. So we’ll
start by reaching back into the depths of our brains and trying to remember the basic
components of an atom.”
Write on board as you speak. Students can use notes and textbooks and should do this
individually. Give them about two minutes.

Draw an atom and its components, labeling the masses and charges.
For students that are more tactile or have disabilities that affect writing, give them three
circles cut out to different sizes (almost equal for proton and neutron, smaller for electron),
and have the student label these circles. Provide varying degrees of pre-written labels (names
of particles, charges, masses) depending on ability of student.
Example hints if needed: “Johnny, maybe these circles will help remind you about
the proton, neutron and electron. Which two do you think are the proton and neutron? And
where do you think you can look up their masses? Which has a positive charge and which
has a negative charge?”
“Turn to your partner, share what you drew, and discuss any points where your drawings
disagree.” (Give them 1-2 minutes.)
“Does anyone want to share what they wrote or drew?”
Clarify to students that protons and neutrons have close but not quite equal masses, whereas
the electron is much lighter. Also, the electron is negatively charged, whereas the proton is
positive and the neutron is neutral.
3. Establish Purpose:
“Something is happening to the protons and neutrons in an atom that leads to radioactivity!
This radioactive event can be used for energy, finding the age of fossils, curing cancer, and
many other things (but not making Spiderman!). But what is happening?? What is
radioactivity and where does it come from?”
B. Presentation & Practice / Application
1. Explain: Have the students explain the discovery of radioactivity to one
another. (30 minutes)
For homework, each student has read and brought in notes about one of three
scientists: 1. Marie Curie, 2. Becquerel, and 3. Rutherford. I’ve made a list of groups of
three, where each member read about a different scientist. These are heterogeneous groups,
where the English Language Learners are paired with more patient and clearly speaking
students, none of the groups have only one woman, and the groups otherwise mix students
of different abilities, backgrounds, and literacy skills.
“You will work in assigned groups to piece together the stories of scientists. You
have the CHOICE to write or draw a page that somehow describes the discovery of
radioactivity. You can write a one page description, a short song, tell a story from the
perspective of a beta particle, or draw a detailed and labeled picture. Just be sure to address
the following guiding questions (write these on board)”:
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Indicate the order of discoveries (and related scientists) that led
to the discovery of radioactivity.

Indicate if alpha, beta, or gamma decay was the first type of
radioactive decay observed, and show/write what was emitted in
this decay.

Indicate three other events you found interesting related to this
discovery.
Vocabulary Activity: “There are some words in your readings that we will be using
repeatedly. So please include and clarify the meaning of the following ten words somewhere
in your description. You can use your textbook and other resources for help. We’ll have a
short quiz on these words tomorrow.”
 Proton
 Electron
 Neutron
 Radioactivity
 Alpha decay
 Beta decay
 Gamma decay
 Electrometer
 Fluoresce
 Ionize

“I’ll read the groups out loud, and then you can gather and rearrange desks. If I don’t
call your name, it means you didn’t hand in your homework, and you will need to read a
handout and hand your one-page description in tomorrow.” (They are 11/12th graders and
accustomed to grouping, so simply call out the groups and they will rearrange the desks).
Give students who didn’t do their homework the attached handout: “Reading on
Radioactive Rays and Particles”.
Give students about fifteen minutes for this activity, regularly circulating and
reminding them about the vocabulary, questions and giving them time warnings.
While they are working, draw a table on the board with columns labeled “Shake
number”, “Predicted number of M’s” and “Actual number of M’s”. (This is for a later
activity.)
Have the students share a few key points with the class. Please ensure that the
following points are clear to the students, and cue all students to have these in their notes.

Bequerel accidentally found that a certain material radiated light onto a
photographic film, and discovered this was due to the presence of uranium.

Marie Curie investigated Becquerel's Rays more systematically with a newly
developed instrument, and more rigorously examined radioactivity. It was a
mystery how energy could be stored in these materials.
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

Ernest Rutherford started identifying rays as alpha and beta based on how far
they penetrated.
Scientists discovered that Beta Rays acted much like electrons – deflected by
magnetic fields and very low mass.
Bring students back to original desk configuration.
2. Explain + Explore: Use Avalanche and M&Ms to explain and explore
concepts of decay and half-life. (10 minutes)
“Based on what we’ve seen so far, it looks like beta particles are electrons being
ejected from the atom when a proton decays into a neutron. But what causes this sudden
change of a proton into a neutron? Why did it happen? Why didn’t it happen before?
Have the students suggest certain mechanisms, and write these on the board.
“This decay is like an avalanche on a snow-covered mountain. The mountain can
stay snow-covered and stable for a very long time, but it reaches a point where it is
inherently unstable. The snow is so heavy that it is ready to fall at the slightest disturbance,
even a slight wind, and when a small amount falls, an avalanche begins and the system
changes drastically.
“In radioactivity, there are random disturbances constantly happening at very small
scales. When one encounters a radioactive isotope, it will cause a sudden decay!”
Print or project this image to help visual students picture what is happening.
http://unofficialnetworks.com/rogers-pass-avy-mows-trees-grass-84267/

Read the explanation in more depth if helpful for oral explanation above:

The decay process, like all hindered energy transformations, may be analogized
by a snowfield on a mountain. While friction between the ice crystals may be
supporting the snow's weight, the system is inherently unstable with regard to
a state of lower potential energy. A disturbance would thus facilitate the path
Shaked: Radioactivity Lesson Plan
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
to a state of greater entropy: The system will move towards the ground state,
producing heat, and the total energy will be distributable over a larger number
of quantum states. Thus, an avalanche results. The total energy does not
change in this process, but, because of the law of entropy, avalanches happen
only in one direction and that is toward the "ground state" — the state with
the largest number of ways in which the available energy could be distributed.
Such a collapse (a decay event) requires a specific activation energy. For a
snow avalanche, this energy comes as a disturbance from outside the system,
although such disturbances can be arbitrarily small. In the case of an excited
atomic nucleus, the arbitrarily small disturbance comes from quantum vacuum
fluctuations. A radioactive nucleus (or any excited system in quantum
mechanics) is unstable, and can, thus, spontaneously stabilize to a less-excited
system. The resulting transformation alters the structure of the nucleus and
results in the emission of either a photon or a high-velocity particle that has
mass (such as an electron, alpha particle, or other type).
“So if we have no idea when a decay is going to happen, how do we know the rate at
which these materials decay? We need to know this rate to be able to estimate the age of
really old objects and fossils.”
http://www.sciencephoto.com/media/221610/view
Pull out wide thin Tupperware of 50 M&Ms (where all M&Ms can lay flat on the
bottom).
“So let’s pretend that each M&M is a radioactive isotope. We’ll start with all the M’s
showing – these can still decay. Now let’s cover it and have someone shake the box. The
shaking represents random fluctuations. While they shake, I want everyone to draw a table
with three columns like the one on the board.”
Bring tupperware to a student that likes touching and seeing things. Some students
will benefit from having a worksheet for this activity, so please hand this sheet out to the
students indicated. These students will gain practice reading and will follow directions better
when presented in written form. They are also still building graphing skills.
“OK, now I’ll have someone remove all the M&Ms that don’t show an M, since
these represent our decayed isotopes. How many Ms are there?” Have student count and tell
Shaked: Radioactivity Lesson Plan
Page 10
the class. Bring Tupperware to another student, while saying “Now we’ll have someone else
shake it. How many Ms do you think will show this time?” Have student count and tell the
class. Do this four or five times until the class seems to be getting the idea.
“Now I want everyone to work with your partner to graph these results, with
“number of shakes” as the x-axis independent variable and “number of Ms” as the
dependent y-axis variable.”
Circulate and make sure they are graphing correctly. They have done this throughout
the year, so it should be straightforward.
“Each shake represents something called a half-life.” Write and say this at the same
time: “A half life is the time it takes for a quantity to decrease to half its value.”
3. Elaborate: Students will work on computers to explore the mechanisms of
radioactive decay and half-life.
Have the students get back into their scientist groups and each group goes to a
computer. Hand out “Beta Decay Simulation” worksheet attached, and give the students 2030 minutes to complete. Circulate and ensure that all students are contributed, partly by
having students switch who is running the computer every five minutes or so.
C. Conclusion of the Lesson:
1. Review Objectives:
Put this slide back up on the computer.
CONTENT OBJECTIVES
1. I can identify the masses and
electrical charges of an atom’s
nucleus – proton, neutron, and
electron.
2. I can creatively explain how scientists
discovered and identified the
properties of beta radiation.
3. I can identify properties of beta
radiation.
4. I can use the concept of a half-life to
predict decay patterns.
5. I can compare and contrast the different
characteristics of alpha, beta and gamma
radiation.
6. I can estimate my own radiation
exposure! I can compare this to other
types of radiation exposure that I
measure in class.
7. I can research and describe real-life
applications of each type of radioactivity.
Shaked: Radioactivity Lesson Plan
LANGUAGE OBJECTIVES
1. I will read and take notes about my
scientist to learn about the process of
science.
2. I will speak and listen to my group
members, so that we can piece
together the history of radioactivity.
We will collaboratively and creatively
write or draw a summary of this
history.
3. I will learn vocabulary related to
radioactivity mechanisms by using
my textbook, my peers, the context of
the word, and my teacher.
4. I will learn vocabulary related to halflives in the same manner as #3.
5. I will clearly and concisely list
comparisons among the different types
of radiation.
6. I will demonstrate my comfort with the
internet, using the internet to estimate
my radiation exposure, and posting the
answer on our class website.
7. I will use the internet and other
resources to research and write about a
real-life application of radioactivity.
Page 11
2. Inquire if Students Have Met the Objectives, How Well? How Do They
Know?
“Let’s see if we’ve met all these objectives. Does everyone have all the bold ones
initialed by me? You’ll need to hand these in, so raise your hand if you don’t, and we’ll go
over them as a class.”
3. Review Key Vocabulary &/or Concepts:
If we didn’t go over vocabulary as a class, we will do that now by having some
students read their paragraph or story or picture to show, demonstrating the definitions of
various words.
4. Connection to Wider Contexts:
“Tomorrow we’re going to measure our own exposure to this radioactivity! And
we’re going to explore ways in which radioactivity is used in the power we get, and in how
we determine the age of things and therefore the history of the world. It is also used to cure
diseases!”
E. Administer, Evaluate, Grade Assessment:
Evaluation is done throughout the class by the teacher, as the students complete
different tasks.
Their in-class stories/reports/drawings are graded that evening to see what they have
understood.
“On an index card, ask two questions about Beta Decay, and hand in.” (2 min.)
This encourages students to ask questions and to think about what they’re not
understanding. It also informs the teacher about what the students are not getting.
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Name: ______________________
Due date: ____________
History of Radioactivity
http://galileo.phys.virginia.edu/classes/252/rays_and_particles.html
More Rays
To return now to 1896, at first nobody had any idea how the x-rays were being generated,
but Roentgen had clearly established that they came from the bit of Crookes' tube glass that
was fluorescing. A French physicist, Henri Becquerel, attended a meeting of the French
Academy of Sciences on January 20, 1896, three weeks after Roentgen's first announcement.
Two French physicians were already showing hand x-rays.
It occurred to Becquerel that any substance that fluoresced intensely might also emit x-rays.
It happened that fifteen years previously he had worked with a substance that fluoresced
strongly when exposed to sunlight, so he wondered if it might also be emitting x-rays,
previously undetected.
To find out, he placed a sheet of it in the sun, lying on top of a cardboard box containing
unexposed film with a small metal object above it. After a day's exposure to the sunlight,
which caused fluorescence, he took out and developed the film. Sure enough, it was exposed
except in the shadow of the metal object, which appeared in silhouette. He decided to check,
and set up the same arrangement again, with a small metal cross above the film.
Unfortunately, however, it continued cloudy, so he kept the package in a closet waiting for
the sun to reappear. After several days Becquerel grew impatient, and, possibly not having
enough to do, decided to develop the film, perhaps to check if some light had leaked in. To
his utter astonishment, he found the silhouette of the cross on the film just as distinctly as
before!
Question for the reader: before reading on, can you figure out any possible
explanation for this surprising discovery? (Write answer here before turning the
page.)
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Page 1
Evidently, the recent exposure to sunlight had not been a crucial element in the production
of the mysterious radiation that had exposed the film. Becquerel theorized that maybe the
substance continued to manufacture rays long after the fluorescence died away. However, it
soon became clear that in fact the fluorescence itself was irrelevant.
It happened that the fluorescent substance Becquerel used for his experiment contained
uranium. After extensive experimenting with various substances, he concluded by May that
the radiation came from any substances containing uranium, whether they fluoresced or not.
He found the intensity of the radiation increased with the amount of uranium present, and
did not appear to change in intensity with time, or temperature, or chemical action. Like xrays, the radiation was ionizing. If a piece of uranium is held near an electroscope, the
electroscope discharges. Unlike x-rays, though, these rays couldn't be turned off.
Marie Curie Investigates Becquerel's Rays
In contrast to all the hoopla over x-rays, Becquerel's rays had little public impact, at least at
the beginning. Fortunately, they did attract the attention of two very talented young
researchers, Marie Curie in Paris and Ernest Rutherford in Cambridge. Marie worked with
her husband Pierre, carefully measuring the amount of radiation from different amounts of
uranium compounds. They measured the radiation by using two parallel metal plates
differing in potential by 100 volts, connected by a sensitive electrometer (basically an infinite
resistance voltmeter, a calibrated electroscope). A thin layer of the uranium compound under
examination was then put on the top plate, and the rate at which charge was lost was
measured - the ionizing radiation caused the charge leakage. Marie concluded that the
radiation intensity was just proportional to the number of uranium atoms present, so the
radiation originated inside the uranium atom. This conclusion was harder to reach than it
sounds, because some fraction of the radiation is absorbed in the material itself. This is why
she used a thin layer, rather than a piece of the material under investigation.
The mineral pitchblende, rich in uranium oxide, was found to be more radioactive than pure
uranium metal. Marie concluded that it must contain some other element that was more
radioactive than uranium. In 1898, the Curies chemically separated out a new element they
called polonium, after Marie's country of birth, Poland. They measured its radioactivity as
four hundred times more intense than that from pure uranium. Six months later, they
chemically separated out from pitchblende another radioactive substance more than one
million times more radioactive than uranium. They called it radium. One gram of radium
gives out enough energy to raise one gram of water from just above freezing to boiling in
one hour. Where this energy could be coming from was a complete mystery. It was hard to
imagine how the energy could be stores in the material - in a few days, radium gave off as
much energy as the most potent chemical fuel, yet it kept on radiating year after year. One
popular theory at the time was that space was full of waves of energy, and almost all
materials were completely transparent to this sea of radiation, but radium, polonium and
uranium absorbed some of this energy and re-emitted it.
Ernest Rutherford Investigates Becquerel's rays
Rutherford worked as a student with J. J. Thomson from 1896, studying the ionization of
gases by x-rays in a quantitative fashion. When Becquerel announced his discovery of new
rays, it was natural for Rutherford to investigate them as well. He began work in Cambridge,
Shaked: Reading on Radioactive Rays and Particles
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but then accepted a job at McGill University in Montreal. He needed some money because
he wanted to get married. He wrote to his fiancee: "I am expected to do a lot of original
work and to form a research school to knock the shine out of the Yankees!" (Pais page 60).
He carefully studied absorption of the Becquerel rays, and found that one component, which
he called the alpha-rays, could be absorbed by a sheet of writing paper, or a few centimeters
of air. In fact, Becquerel had not detected these alphas, because they were absorbed by the
box containing the film. A second component, the beta rays, Rutherford found to be one
hundred times more penetrating. He published this result in 1899. In 1900, Rutherford went
home to New Zealand and got married. French physicists, meanwhile, kept up the pace of
discovery. Villard found that radium emitted some far more penetrating radiation, which he
christened gamma rays. These rays could penetrate several feet of concrete.
Identifying the Beta Rays
It was clear by 1900 from their deflection by a magnetic field that the beta rays were
negatively charged particles. In that year, Becquerel found e/m for beta rays to be quite close
to that for cathode rays, suggesting that they also were electrons. One difference between the
beta rays and cathode rays was that the beta rays could be much faster - up to 95% of the
speed of light. By 1902, a German physicist, Kaufman was writing: "for small velocities,
..[e/m for] Becquerel rays … fits within experimental error with the value found for cathode
rays." The interesting historical point here is that physicists already expected that mass might
change with speed. There were complicated (and wrong) electromagnetic theories about how
the mass might vary, beginning with the idea that the kinetic energy of a charge moving
through the ether included energy from the ether flowing around it - an idea based on earlier
analyses of the motion of a sphere through a real fluid. Lorentz contraction effects were
added to give yet more complicated formulas. However, in 1908, a German experimenter,
Bucherer, claimed that the best fit to the e/m data was given by Einstein's much simpler
recent formula for mass variation with speed. These experiments were difficult to do, and
Bucherer's results were not universally accepted until about 1916, by which time others had
found the same results.
Shaked: Reading on Radioactive Rays and Particles
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Name: ______________________
Due date: ____________
Half-life Simulation
http://alex.state.al.us/lesson_view.php?id=24005
Introduction:
Half-life is the time required for one half of a radioactive material to decay or change into something
else. Radioactive atoms have nuclei that are unstable. These nuclei become more stable by emitting
particles or rays. The half-life of an isotope is characteristic of that isotope. The value can be from
fractions of a second to billions of years. Half-life values are constant - there is no way to speed up or slow
down this natural process.
Purpose:
To simulate the process of radioactive decay and determine the “half-life” for the process.
Procedure:
Each M & M will represent at atom of a radioisotope. The M & Ms in the baggie are thoroughly
mixed and poured out onto the paper plate. Those M & Ms with letters showing are still "radioactive". The
others have "decayed" and should be removed. Count the numbers of "atoms" removed and record the
values in the data table. Return those M & Ms which have the letters showing to the bag, shake, and pour
onto the paper plate. Again, count the number of M & Ms with no letters showing. Record and continue.
When the data has been collected, plot the data (atoms left vs. trial number) and draw a smooth curve
through the points.
The value for the half-life is obtained as follows:
1.
Select two values on the y-axis (not necessarily data points). One value should be half as large as the
other (60 & 30 for example).
2.
Draw lines from these points to your line. This marks the decay of half of a sample.
3.
Next, vertical lines should be drawn from where these lines intersect your lines to the x-axis. The
space between these lines on the x-axis is the half-life. This is the amount of time required for half of
the radioisotope to decay, that is, the half-life.
Shaked: Half-life M&M Simulation
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Name _________________________
Name _________________________
Period ______Date_______________
Data:
Original Number of Atoms _______________
Trial
Atoms Decayed
Atoms Left
1
2
3
4
5
6
7
8
9
10
Half-life computed from the graph: __________________________
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Half-Life Simulation Graph
100
90
80
Counts of Radiation
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
Time in Years
(treat each trial as if there was 1 year between them)
Shaked: Half-life M&M Simulation
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Name: ______________________
Due date: ____________
Beta Decay Simulation
http://phet.colorado.edu/en/contributions/view/3559
Learning Goals: Students will be able to:
 Describe the process of Beta decay
 Compare the meaning of “Half-life” for Alpha and Beta decay.
Directions: Open Beta Decay
1. Investigating “Beta Decay”
a. Start on the Single Atom tab - observe the decay of Hydrogen-3 and Carbon- 14. Use
Reset Nucleus to watch the process repeatedly. Write a description of what happens in
the beta decay of an atom.
b. Check your ideas with the “Custom” atom and reflect on your ideas.
New ideas here:
c. Verify your ideas by using online resources to determine what the differences are
between Hydrogen-3 and Helium-3 as well as Carbon-14 and Nitrogen-14. Also, use other
resources to see what “Beta Decay” means and cite at least one valid source.
Cites here:
d. Practice using your ideas by predicting what would happen if the following undergo beta
decay:
i. Carbon -10  __________+ _____
ii. Cesium-137  __________+ _____
iii. Thorium-234  __________+ _____
e. Practice using your ideas by predicting what would happen Uranium-238 undergoes
alpha decay and then beta decay.
Uranium-238
2. Investigating “Half-life” for Beta Decay
Shaked: Beta Decay Simulation
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a. Use the Charts at the top of the sim to test ideas you might have about half-life. Make sure
to use multiple samples and substances with a variety of half-lives. Make a data table that
shows your tests.
Data Table here:
b. In your own words, describe what “half-life” means for Beta Decay.
3. Check your ideas by drawing predictions without using the sim for the following scenario:
If you have a substance that has a half- life of 20 years make predictions of what will happen
by sketching the pie graphs indicating the number of the substance and it’s decayed atoms for
a reaction starting with 100 total atoms.
t= 5 years
d.
t=10 years
t=20 years
Use the sim to test the scenario. Copy the graphs. ( Pause
t= 5 years
t=10 years
t=30 years
and Step
t=20 years
may help)
t=30 years
t=2s
e.
How do your predictions compare to the results shown in the sim?
f.
What ideas do you have to explain the similarities and differences in the data and also
your predictions?
Shaked: Beta Decay Simulation
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Name: ______________________
Due date: ____________
Half-Life Practice
http://quarknet.fnal.gov/materials/fnal-guide.pdf
1. What is half-life?
2. If you have 100 g of a radioactive isotope with a half-life of 10 years:
a. How much of the isotope will you have left after 10 years?
b. How many half-lives will occur in 20 years?
c. How much of the isotope will you have left after 20 years?
3. The half-life of plutonium-239 is 24,300 years. If a nuclear bomb released 8 kg of this
isotope, how many years would pass before the amount is reduced to 1 kg?
4. The half-life of radon-222 is 3.8 days. How much of a 100-g sample is left after 15.2 days?
5. Carbon-14 has a half-life of 5,730 years. If a sample contained 70 mg originally, how much
is left after 17,190 years?
6. How much of a 500-g sample of potassium-42 is left after 62 hours if its half-life of 12.4
hours?
7. The half-life of cobalt-60 is 5.26 years. If 50 g are left after 15.8 years, how many grams
were in the original sample?
Shaked: Half-Life Practice
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8. The half-life of I-131 is 8.07 days. If 25 g are left after 40.35 days, how many grams were in
the original sample?
9. If 100 g of Au-198 decays to 6.25 g in 10.8 days, what is the half-life of Au-198?
10. Graph the following data on the graph paper, then use the graph to determine the half-life of
this isotope.
Shaked: Half-Life Practice
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