Download Half-life and Radioactive Decay guided notes

Half-Life and Radioactive Decay
My Goals for this Lesson:

Distinguish between nuclear and chemical reactions.

Compare and contrast different types of nuclear reactions.

Describe and make predictions regarding half-life.
I’m preparing to distinguish between nuclear and chemical reactions, compare and contrast different
nuclear reactions and understand half-life and how to predict it for a given situation.
Introduction
Answer the following questions in your own words using what you learned from the introduction.
What is Carbon 14 dating?
Who first developed the technique and when?
What is Carbon 14?
Why can we use Carbon 14 to “date” once living remains?
How do scientists do Carbon 14 dating?
What assumption do scientists make in doing Carbon 14 dating?
Who is Jim Chatters?
Who is Kennewick Man?
What does Carbon 14 dating have to do with them?
Be sure to have watched the Discovery Education™ Streaming video to help you see how carbon 14
dating is used in science.
Lesson
Fill in blanks using the Lesson.
Nuclear reactions arise from an atom’s
. Nuclear radiation occurs
in the rocks and
soil around us, in the air we breathe, and even in the food we eat. There are also nuclear reactions that
are used by humans to
our society. These reactions play an important role in medical
diagnostics and radiation therapy and can also be used in nuclear power plants to convert nuclear energy
to electricity. Reactions occurring in the
energy. Because of the
are our planet’s most significant source of nuclear
, and sometimes
, roles that nuclear reactions and
radiation play in the world around us, it is a good idea to have a basic understanding of nuclear reactions.
“Did you know?”
What does this symbol mean?
Chemical vs. Nuclear Reactions
Atoms are made up of
,
, and
. In the chemical reactions that we have
studied throughout this course, the sharing or exchange of
compounds while the
and
However, some atoms have
Atoms with
was involved in forming bonds and
remained unchanged in the nuclei of the atoms.
nuclei because the number of protons and neutrons are
nuclei are
balance.
; they eventually break down into a different substance
and release energetic particles, or radiation, in the process.
Radiation Therapy
What does the lesson tell you about radiation therapy?
Alpha, Beta, and Gamma Rays
Fill in the blanks using the tabs in the lesson.
Alpha (α) Radiation
Alpha radiation is made up of a stream of
particles. Alpha particles are made up of
protons
and two neutrons released from the nucleus of the radioactive atom. This means that alpha particles
have a
charge, and that when an atom releases an alpha particle, its atomic number
by two and its mass number decreases by four.
Alpha particles have a high amount of
energy and can cause
such as skin and living tissue. However, alpha particles are relatively easy to
cannot normally penetrate
to surface materials
against. They
materials such as paper or fabric. Also, as they travel through
the air, the particles attract electrons and become
helium atoms.
Beta (β) Radiation
Beta radiation is made up of a stream of beta particles. Beta particles are fast-moving
released from a nucleus when a neutron
apart into one proton and one electron.
A negative beta particle, which is a very fast moving electron, is released when a neutron
positive
.A
is left behind in the nucleus during this type of decay.
When the negative beta particle is released from the nucleus of an atom, the atom ends up with one
more
and one less
.
Beta particles have a negative charge and they usually move
that beta particles are more
than alpha particles. This means
to protect against than alpha particles; they can penetrate
cloth and paper. Beta particles can penetrate deeply into skin and potentially
However, these particles cannot penetrate thin layers of
living cells.
materials such as
and other metals. When beta particles are finally stopped by a substance, they are
material, like any other electron.
or
by the
Gamma (γ) Radiation
Gamma radiation can be given off during different types of nuclear decay. Gamma rays are a form of
electromagnetic
with a very high frequency and
energy than ultraviolet light or X-rays.
Because gamma rays have high energy and no mass or charge, they can penetrate through
materials. Gamma rays can cause much
very
damage to living cells than alpha or beta particles. Only
materials, such as thick layers of lead, can stop gamma rays. This is why
is
commonly used as a shielding material in laboratories and hospitals where gamma radiation is present.
Overview
Use the Overview tab to complete this chart using your own words.
Alpha (α)
Beta (β)
Gamma (γ)
Description
Movement
Impact on humans
Radioactive Decay
Fill in the blanks and chart using the lesson.
When a
element’s nucleus decays and gives off an alpha or beta particle, the number of
protons and neutrons inside the nucleus
. When this happens, the atom becomes another
element. This is what makes nuclear reactions
reaction, the
of the elements actually
than regular chemical reactions. In a nuclear
, because protons and neutrons are gained
or lost by the atom over the course of the reaction.
Produces
Radioactive uranium-238
Thorium-234
Leaves Behind
Describe the energy
released
The decay of uranium-238 involves a series of alpha and beta decays that eventually produce
.
The table shows the series of nuclear-decay reactions that occur. Take some time to examine how the
atomic number and mass number changes for each reaction and identify them as alpha or beta decay.
Be sure to do the “Let’s Review” section on the Activity page.
Half-Life
Fill in the blanks using the lesson.
Radioactive isotopes
substance’s
at different rates, but the rates are all measured in terms of the
. Half-life is the
decay. The half-life of a given
needed for
of the radioactive atoms in a sample to
is constant and is independent of
conditions or the
amount of atoms in the sample. This means that the half-life of a specific isotope will be the
whether you have one million moles or one mole of the atoms.
The graph below represents the radioactive decay of a hypothetical element. Notice that the time it
takes for the amount of radioactive material to decrease from 1.0 to 0.5 is the same as the amount of
time it takes to decrease from 0.25 to 0.125. This time interval, marked as t½ on the graph, represents
the half-life of this radioactive substance and is independent of the amount of radioactive substance
remaining in the sample.
The graph represents the decay of a radioactive element and illustrates how the data can be used to
determine the half-life of the substance. The amount of radioactive element remaining in the sample,
measured in moles, percentage, grams, or radioactivity detected, is on the vertical y axis of the graph.
Time, measured in seconds, minutes, days, or years, is on the horizontal x-axis.
The rate of radioactive decay, like any other rate, gives a curved line as the amount of the radioactive
substance remaining decreases over time. The amount of time it takes for only half of the original
sample to remain is equal to the amount it takes for the radioactive sample to decrease from one-half to
one-quarter of the original amount. For example, if it took twenty days for the sample to decrease from
one hundred moles to fifty moles of radioactive material, it would take another twenty days for the
sample to decrease from fifty moles to twenty five moles of radioactive material remaining.
Radium-226 has a half-life of 1,620 years, which means that half of a given sample of radium-226 will
decay into lead by the end of 1,620 years. In the next 1,620 years, half of the remaining sample will
decay into lead, leaving one-fourth of the original amount of radium-226.
The half-lives of radioactive substances range from less than a millionth of a second to more than a
billion years. Uranium-238 has a half-life of 4.5 billion years! So how can scientists measure half-lives
that are that long? The answer is that they do not measure the actual half-life, but they can accurately
measure the rate of the isotope’s decay using a radiation detector. The faster a substance decays, the
more radiation per minute is detected, and the shorter the half-life of a given isotope. It is not
necessary to wait through an entire half-life of a substance; the half-life can be calculated using the
rate of decay that is observed.
Once we know the half-life of a substance, this information can be used to estimate the age of ancient
remains. One of the most common examples of this is the use of carbon-14 dating to estimate the age of
dead organisms or artifacts made of wood or cloth.
Radiation Detectors
Use the interactive section on Radiation Detectors to complete this chart.
Image
Description
Be sure to do the “Let’s Practice” section on the Activity page.