Download Radioactivity and Nuclear Reactions

Radioactivity and Nuclear
Reactions
Section 1: Radioactivity
• Review
– What are atoms composed of?
– What is the charge of each of the particles?
– Where is each particle located?
– What is the atomic number?
The Strong Force
• The strong force causes protons and neutrons to
be attracted to each other.
• The strong force is about 100 x greater than the
electric force (the force that would cause the
protons to repel each other).
• The strong force is a short range force that
quickly becomes extremely weak as protons and
neutrons get farther apart.
Radioactivity
• radioactivity—process of nuclear decay
• All nuclei that contain more than 83
protons are radioactive.
• Almost all elements with more than 92
protons don’t exist naturally on Earth.
They have been produced only in
laboratories.
Isotopes
• isotopes—nuclei having the same number
of protons but different numbers of
neutrons
• The atoms of isotopes of an element have
the same number of electrons and the
same chemical properties.
Nucleus Numbers
Discovery of Radioactivity
• Henri Becquerel accidentally discovered radioactivity in
1896.
• Pierre and Marie Curie, shown here in their laboratory in
Paris, helped pioneer the study of radioactivity, unaware
of the deadly hazards. Even with deteriorating health,
the Curies continued their research. Much of today’s
nuclear science is based on their work.
Section 2: Nuclear Decay
• When an unstable nucleus decays,
particles and energy are emitted from the
decaying nucleus.
• These particles and energy are called
nuclear radiation.
• The three types of nuclear radiation are
alpha, beta, and gamma radiation.
Alpha Particles
• An alpha particle is made of two protons
and two neutrons bound together.
• charge: +2
• atomic mass: 4
Transmutation in Alpha Radiation
• When an atom loses an alpha particle, it no
longer has the same number of protons, so it no
longer is the same element.
• Transmutation is the process of changing one
element to another through nuclear decay.
Beta Particles
• Sometimes in an unstable nucleus, a
neutron decays into a proton and releases
an electron.
• beta particle: the electron emitted from
the nucleus during beta decay
• Beta decay is caused by the weak force.
Transmutation in Beta Radiation
• During beta decay, the atom now has one more
proton so it becomes the element with an atomic
number one greater than that of the original
element.
• Since the neutron decays into a proton, the total
number of protons and neutrons does not
change during beta transmutation, so the atomic
mass number stays the same.
Gamma Rays
• Gamma rays are a form of radiation called
electromagnetic waves (so they carry energy).
• They have no mass and no charge.
• They travel at the speed of light and are usually
released along with alpha and beta particles.
• Because gamma rays only transfer energy and
not particles, no transmutation occurs.
Comparison of the Three Types of
Nuclear Radiation
• Compared to beta particles and gamma
radiation, alpha particles are much more
massive.
• Alpha particles also have the most electric
charge.
+2 compared to -1 compared to no charge
Comparison of the Three Types of
Nuclear Radiation—continued
• Alpha particles are the least penetrating
form of nuclear radiation.
• Alpha particles cannot even pass through
a sheet of paper.
Comparison of the Three Types of
Nuclear Radiation—continued
• Beta particles are much faster and more
penetrating than alpha particles.
• They can pass through paper but are
stopped by a sheet of aluminum foil or
plastic..
Comparison of the Three Types of
Nuclear Radiation—continued
• Thick blocks of dense material, such as
lead and concrete, are required to stop
gamma rays.
Comparison of the Three Types of
Nuclear Radiation—continued
Radioactive Half-Life
• The half-life of a radioactive isotope is the
amount of time it takes for half the nuclei
in a sample of the isotope to decay.
• The nucleus left after the isotope decays is
called the daughter nucleus.
Radioactive Dating
• Carbon Dating
– The half-life of a carbon-14 atom is 5,730
years.
– The age of the remains of plants and animals
that lived within the last 50,000 years can be
measured using carbon-14.
• Uranium Dating
– can be used to measure the age of rocks
Carbon Dating
Section 4: Nuclear Reactions
Nuclear Fission
• nuclear fission—process of splitting a
nucleus into two nuclei with smaller
masses
• Only large nuclei, such as the nuclei of
uranium and plutonium atoms, can
undergo fission.
• The products of fission usually include
several individual neutrons in addition to
the smaller nuclei.
• The small amount of missing mass is
converted to a tremendous amount of
energy.
Chain Reactions
• A chain reaction is an ongoing series of
fission reactions.
• Billions of reactions can occur each
second during a chain reaction, resulting
in the release of tremendous amounts of
energy.
Critical Mass
• The critical mass is the
amount of fissionable
material required so that
each fission reaction
produces approximately
one more fission reaction.
• Nuclear power plants use
control rods made of
nonfissionable material
that can absorb neutrons.
• The control rods are
moved in and out of the
fissionable material to
control the rate of the
chain reaction.
Nuclear Fusion
• In nuclear fusion, two nuclei with low
masses are combined to form one nucleus
of larger mass.
• Temperature and Fusion
The Sun
• Most of the energy given off by the Sun is
produced by a process involving the fusion
of hydrogen nuclei.
• Earth receives a small amount of this
energy as heat and light.
Using Nuclear Reactions in Medicine
• What is a tracer?
• What can tracers be used for?
• What happens to the cells in a person’s
body when they have cancer?
• How can radiation be used to treat
cancer?
• How can physicians be sure that only
cancer cells will absorb radiation?