Transcript Radioactive Decay

ACADs (08-006) Covered
1.1.4.2
3.3.1.1
3.3.1.7
4.9.1
4.9.7
Keywords
Radioactivity, radioactive decay, half-life, nuclide, alpha, beta,
positron.
Description
Supporting Material
OBJECTIVES
• Define the following terms associated with
radioactive decay:
–
–
–
–
radioactivity
radiation
radioactive decay
half-life
• State the difference between radioactivity and
radiation.
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OBJECTIVES
• Using the Chart of the Nuclides and given a
stable nuclide, determine the following:
– Element Name
– Atomic Number (A)
– Atomic Mass (Z)
– Isotopic Mass
– Atom Percent Abundance (%)
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OBJECTIVES
• Using the Chart of the Nuclides and given a
man-made radioactive nuclide, determine the
following:
– Element Name
– Atomic Number (A)
– Atomic Mass (Z)
– Half-Life
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OBJECTIVES
• Describe the following types of decay in terms
of the requirements for and mode of
occurrence, the resulting products, and
emissions:
– Alpha
– Beta
– Positron
– Electron capture
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PRESENTATION
RADIOACTIVE DECAY TERMS
• Radioactivity is defined as “that ability of an
unstable nucleus to spontaneously emit
particles and/or energy to achieve a more
stable state.”
• Radiation is defined as “energy or particles
propagated through space.”
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RADIOACTIVE DECAY TERMS
• Radioactive decay is defined as “that process
in which an unstable nucleus spontaneously
emits particles and/or energy to achieve a
more stable state.”
• Half Life (t1/2), is defined as “the time required
for one-half of the nuclei of a given radioactive
material to undergo radioactive decay.” Half
Life is unique to each nuclide and is expressed
in seconds, minutes, hours, days, or years.
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RADIOACTIVITY v.s. RADIATION
Radioactivity
The spontaneous
nuclear transformation
that usually results in
the formation of a
different nuclide.
Radiation
Energy or particles
propagated through
space.
Be sure you know the difference
between these two. They are not the
same!!
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RADIOACTIVE DECAY
• As mass numbers of nuclei become larger,
the neutron to proton ratio becomes larger
for the stable nuclei.
• Non-stable nuclei may have an excess or
deficiency of neutrons and undergo various
decay processes such as beta (- or +),
alpha (), neutron (n), or proton (p) decay.
• The result of these decay processes
provides a more stable configuration.
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RADIOACTIVE DECAY
CHART OF THE NUCLIDES
Chart of the Nuclides
The Vertical Column of Numbers lists
the Atomic Number or “Z Number”
for each associated row. It describes
how many protons are in that row
Z
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Chart of the Nuclides
The Horizontal Row of Numbers lists
the “N Number” for each associated
column. It describes how many
neutrons are in that column.
N
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Chart of the Nuclides
Each box in the chart contains information
about that particular nuclide.
Let’s look at some examples.
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Chart of the Nuclides
Chemical
Element
H
1.00794
Hydrogen
a .333,.150
- Symbol
- Atomic Weight (Carbon -12 Scale)
- Element Name
- Thermal Neutron Absorption
Cross-Section in Barns Followed by
Resonance Integral, in Barns
These are the heavily bordered
Squares at the end of each row.
Atomic weight
It contains the chemical symbol
Thermal neutron
and properties of the element
absorption cross-section
as found in nature.
These properties include:
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Stable Nuclides
- Symbol, Mass Number
Atom Percent Abundance Thermal Neutron Capture Cross-Sections in
Barns Leading to (Isomeric + Ground State),
Followed by Resonance Integrals Leading to
(Isomeric + Ground State).
Isotopic Mass (Carbon - 12 Scale) -
This box contains
the following
information:
Chemical symbol with
Thermal neutron
atomic mass number.
absorption cross section
A stable nuclide
Isotopic abundance (%)
is naturally
Isotopic mass of
stable and found
neutral atom on C12
in nature.
scale
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Long-Lived, Naturally Occurring Radioactive
Nuclides
Naturally Occurring or Otherwise
Available but Radioactive
Symbol, Mass Number -
Modes of Decay in Order of Prominence with
Energy of Radiation in MeV for Alpha and
Beta; keV for Gammas.
La 138
0.090
1.05e11 a
5+
, -.25
 1435.8, 788.7
 ~57,4E2
E 1.04 137.90711
- Atom Percent Abundance
- Half-Life
- Beta Disintegration Energy Followed by
Isotopic Mass
Thermal Neutron Capture Cross-Section,
Followed by Resonance Integral.
The black
rectangle indicates
that the isotope
is radioactive and
found in nature.
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Squares with both black
rectangles and gray
represent naturally
occurring isotopes with a
very long half life.
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Long-Lived, Naturally Occurring Radioactive
Nuclides (more)
Naturally Occuring or Otherwise
Available but Radioactive
Symbol, Mass Number -
Modes of Decay in Order of Prominence with
Energy of Radiation in MeV for Alpha and
Beta; keV for Gammas.
La 138
0.090
1.05e11 a
5+
, -.25
 1435.8, 788.7
 ~57,4E2
E 1.04 137.90711
- Spin and Parity
- Atom Percent Abundance
- Half-Life
- Beta Disintegration Energy Followed by
Isotopic Mass
Thermal Neutron Capture Cross-Section,
Followed by Resonance Integral.
Isotopic
abundance (%)
Decay modes
and decay
energies in MeV
for ,; keV for .
Chemical symbol with
atomic mass number.
Half-Life
Isotopic mass of
neutral atom on C12
scale
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Man-Made Radionuclides
Artificially
Radioactive
S38
2.84 h
Modes of Decay with Energy of Radiation in
MeV for Alpha and Beta; keV for Gammas.
- Symbol, Mass Number
- Half-Life
- .99, ...
 1941.9 ...
E 2.94
- Beta Disintegration Energy in MeV.
Chemical symbol with
atomic mass number.
Decay modes in MeV for
,; keV for .
Half-Life
Emax of Beta Energy
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LINE OF STABILITY
Note that there is a
line of stable atoms
(gray boxes) that run
diagonally through the
entire Chart of the
Nuclides.
This is known as the
“Line of Stability”. It is
where all radioactive
isotopes will eventually
come to rest after one
or more decay events.
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ACADs (08-006) Covered
3.3.1.7
4.91.
Keywords
Description
Supporting Material
TYPES OF RADIOACTIVE DECAY
• There are many types of Radioactive
Decay. We will discuss the following:
– Alpha particle emission
– Beta emission (both - and +);
– Gamma emission
– Electron capture
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ALPHA EMISSION DECAY
• A large, loosely packed nuclei will decay by
alpha emission. An alpha particle () is
released from its nucleus.
• An alpha particle () is a Helium (He) nucleus
(a Helium atom minus its two electrons).
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ALPHA DECAY
In Alpha decay 2 neutrons and 2 protons are emitted
forming an  particle.

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ALPHA EMISSION DECAY
• The Helium nucleus has two (2) protons, and
two (2) neutrons.
• When released from the original nucleus, the
new nucleus will have an Atomic Number
two less than its original and an Atomic mass
of four less than its original.
• Let’s look at a couple of graphic
demonstrations of this type of decay on the
Chart of the Nuclides.
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A
L
P
H
A
D
E
C
A
Y
Old
Isotope
New
Isotope
N -2
N -1
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EXAMPLE
Americium 242 emits an  and transforms into Neptunium 238
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BETA MINUS DECAY
• In a beta minus (-) decay, a nuclei emits a
negative charge from the nucleus.
• A - is identical in charge and mass of an
electron.
• In - decay, a neutron is converted to a proton,
causing the nuclide’s Atomic Number to
increase by one (1), but the Atomic Mass to
stay the same.
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BETA MINUS DECAY
In Beta minus decay a neutron changes to a proton with
the emission of a -.
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BETA MINUS DECAY
• - decay is the primary emission mode of
radioactive nuclides that are born below the
Line of Stability.
• Let’s look at a couple of graphic
demonstrations of this type of decay on the
Chart of the Nuclides.
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New
Isotope
D
E
C
A
Y
Old
Isotope
N -2
N -1
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EXAMPLE OF

DECAY
Cesium 137 emits a - and transforms into Barium 137
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POSITRON (+) DECAY
In Positron decay, a proton changes to a neutron with the
emission of a + .
Besides the
emission of a +, the
Atomic Number (A
number) of the
nucleus goes down
by 1 and the Atomic
Mass (Z number)
stays the same.
+
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ELECTRON CAPTURE ()
In Electron Capture an electron is captured by the nucleus,
changing a proton to a neutron with the emission of a
characteristic X-Ray and a +.
The end results
are the same
as a + decay
discussed
previously. The
A number goes
down by 1 and
the Z number
stays the
same.
X-ray
+
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EXAMPLE OF
+
 AND
 DECAY
Lanthanum 136 captures an electron or emits a + and
transforms into Barium 137
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+ C
or A
P
E
T
L
U
E
R
C
E
T
R D
O E
N C
A
Y
Old
Isotope
New
Isotope

N -2
N -1
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N +1
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SUMMARY
• Summarize Objectives with students.
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