Download Quarter 1 Unit 3 Radioactivitypptx

1.3-1 Types of Radioactivity
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By the end of this section you will be
able to:
◦ Observe nuclear changes and explain how they
change an element.
◦ Express alpha and beta decay in nuclear equations.
◦ Model the half life of an isotope.
◦ Explain how half life is used to date materials.
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Radioactivity
Alpha Particle
Beta Particle
Alpha Decay
Beta Decay
Gamma Decay
Half life
Radioactive Dating
Radioactive Decay
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Radioactivity is the spontaneous
emission of radiation by an unstable
atomic nucleus.
Chemical Reactions vs. Nuclear Reactions
Occur when bonds are broken
and formed
Occur when nuclei combine,
split and emit radiation
Involve only valence electrons Can involve protons, neutrons
and electrons
Atoms keep the same identity
although they gain, lose or
share electrons
Atoms of one element are
often converted into atoms
of another element
Associated with small changes
in energy
Associated with large
changes in energy
Temperature, pressure,
concentration and catalysts
affect reaction rates
Temperature, pressure,
concentration and catalysts
do not affect reaction rates
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Nuclear reactions involve the protons and
neutrons found in the nucleus
During nuclear reactions a nucleus can gain or
lose protons and neutrons.
 Remember
that the number of protons
determines the identity of an element.
◦ Changing the number of protons changed
the element into another element.
◦ During nuclear reactions atoms
of one element are changed into
atoms of another element
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Different isotopes of atoms can be represented
using nuclear notation.
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In your notebook write the following isotopes
in nuclear notation.
◦ Hydrogen-1
◦ Hydrogen-2
◦ Hydrogen-3
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http://www.youtube.com/watch?v=pYb9yZ22v
Qk&safe=active
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Radioactive decay is the release of radiation by
radioactive isotopes.
Not all radioactive isotopes decay in the same way.
◦ Different types of decay change the nucleus in
different ways.
 The three types of decay are:
 Alpha
 Beta
 Gamma decay
 Alpha decay is the release of alpha
particles (2 protons and 2 neutrons).
 Alpha particles are helium nuclei consisting
of two protons and two neutrons.
 Alpha particles are represented as
or α.
•
Alpha particles, which are large in
size, collide with objects around
them.
 Do not penetrate very deeply
 Are easily stopped by a thin layer of
material.
◦ Alpha decay causes the decaying nucleus to lose
2 protons and 2 neutrons.
◦ This means:
 the mass # decreases by 4 (2P and 2N)
 The atomic # decreases by 2
 Examples
◦ Parent
Daughter
alpha particle
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The parent element turns into a
daughter element with a mass number 4
less and an atomic number 2 less than the
parent!
Does this reaction demonstrate the law of
conservation of matter?
◦ How can we check it? Explain
Two protons and
neutrons are lost
The protons and neutrons
leave as an alpha particle.
+ Energy!
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Write the equation for alpha decay for
the following particle in your notebook.
 Thorium-230
Beta decay is the release of beta particles
from a decaying nucleus.
◦ A beta particle is a high energy electron with a
1- charge.
 Beta particles are written as
β- or
 Beta particles pass more easily through matter than
alpha particles and require sheets of metal, blocks of
wood or specialized clothing to be stopped.
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The electron released during beta decay is not one
of the original electrons that existed outside the
nucleus.
The beta particle (electron) is produced by the
change of a neutron into a proton and an
electron.
Mass# is same!
◦ Parent
Daughter Beta
(add P+) (sub e-)
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The parent nucleus turns into a
daughter with an atomic number 1
greater.
The mass number stays the same.
•A neutron becomes a proton (which stays
in the nucleus) and electron (which is
ejected from the atom).
•ADD A PROTON and LOSE an ELECTRON
+ ENERGY
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Write the equations for beta decay for
the following particles.
 Magnesuim-27
 Sulfur-35
 Gamma
decay is the release of gamma
rays from a nucleus.
◦ A gamma ray is a high energy form of
electromagnetic radiation with out a
change in mass or charge.
◦ Gamma rays have high
penetrating ability and are very
dangerous to living cells.
◦ To stop gamma rays thick blocks of lead or
concrete are needed.
 During
gamma decay only energy is
released!
◦ Gamma decay does not generally occur
alone, it occurs with other modes of
decay. (alpha or beta)
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When gamma decay is expressed in an equation
it is expressed as γ.
◦ Electron from beta decay is captured to cause
gamma particle to emit.
◦ The following equation shows both gamma and alpha
decay occurring.
Beta emission
Co-60
 Ni-60 + Beta e-  Ni-60 + gamma photon
(excited state)
(particle of radiation)
Decay Type
Alpha
Beta
Gamma
Gives off
Changes Nuclear Radiation
notation by:
penetration and
harm to cells
Alpha
Decay
Type
Gives off
Changes Nuclear
notation by:
Radiation penetration and
harm to cells
2 protons &
2 neutrons=
Alpha
particle=
•Mass number
decreases by 4
•Atomic number
decreases by 2
•Large particle, easily stopped
by cloth
•Very low risk
Atomic number
increases by 1
The mass number
stays the same
•These high energy particles
pass more easily through
matter
•Need metal sheets to stop
•Moderate risk to cells
•No change in
mass or atomic
number
•BUT does not
occur alone
•Accompanied by
alpha or beta.
•Gamma rays have high
penetrating ability
•To stop gamma rays thick
blocks of lead or concrete are
needed.
• Very dangerous to living
cells.
4
2
He
Gamma
Beta
Beta particle
= electron =
e
0
-1
A gamma ray
a high energy
form of
electromagnetic
radiation
PLEASE DO NOT WRITE THE QUESTIONS!
Each correctly answered question is worth 1 point!
1.
What are the three types of decay?
2.
Explain what occurs to the element in each type
of decay, be specific.
◦
A.
B.
C.
3.
4.
5.
Which type of decay is least harmful to living
cells.
Which is most harmful?
If Uranium-238 alpha decays, what would the
decay equation be?
Alpha, beta and gamma
2. Alpha- gives off alpha particle which is 2 protons
and 2 neutrons. It reduces the atomic number by
2 and the mass by 4 so becomes a new element
Beta- a neutron becomes a proton and an
electron and gives off the electron, it adds 1 to
the atomic number but leaves the mass number
the same so a new element is formed
Gamma- just a gamma ray, pure electromagnetic
radiation (energy)
3. Alpha
4.Gamma
5 238 U -> 234 Th + 4 He
92
90
2
1.
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Radiation can be detected with Geiger
counters and scintillation counters.
◦ Geiger counters detect ionizing radiation.
◦ Scintillation counters register the
intensity of radiation by detecting light.
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It is impossible to predict when a specific
nucleus in a sample of radioactive material
will undergo decay.
The rate of overall decay is constant so
that it is possible to predict when a given
fraction of a sample will have decayed.
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Half-life is a term used to describe
the time it takes for half of a given
amount of a radioactive isotope to
decay.
◦ Half-life varies greatly depending on
the isotope
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Radioactive decay has provided scientists with a
technique for determining the age of fossils,
geological formations and human artifacts.
◦ Four isotopes are commonly used for dating
objects
 Carbon-14
 Uranium-238
 Rubidium-87
 Potassium-40
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Carbon-14 Dating
◦ All organisms take in carbon during their lifetime.
◦ When organisms die they stop taking in carbon.
 Most carbon that organisms take in is stable (Carbon-12
or Carbon-13).
 About one atom in a million is Carbon-14.
 While the organism is alive the amount of Carbon-14 in
its tissues remains constant.
 After the organism dies no more Carbon-14 is taken
in and the amount begins to decline at a
predictable pace. (half-life of C-14=5730 years)
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The half-life of Carbon-14 is 5730 years.
◦ Objects greater than 60,000 years old cannot be
dated using this method because the amount of
Carbon-14 that remains is too small to be
detected.
 Objects greater than 60,000 years old are
dated using:
 Uranium-238 (t½ = 4.5 billion years)
 Rubidium-87 (t½ = 48 billion years)
 Potassium-40 (t½ = 1.25 billion years)