Transcript Chapter

Chemistry: A Molecular Approach, 2nd Ed.
Nivaldo Tro
Chapter 19
Radioactivity
and Nuclear
Chemistry
Roy Kennedy
Massachusetts Bay Community College
Wellesley Hills, MA
Copyright  2011 Pearson Education, Inc.
Nuclear Medicine
• Changes in the structure of the nucleus are
•
used in many ways in medicine
Nuclear radiation can be used to visualize or
test structures in your body to see if they are
operating properly
e.g. labeling atoms so their intake and output can
be monitored
• Nuclear radiation can also be used to treat
diseases because the radiation is ionizing,
allowing it to attack unhealthy tissue
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The Discovery of Radioactivity
• Antoine-Henri Becquerel
designed an experiment to
determine if phosphorescent
minerals also gave off X-rays
phosphorescence is the long-lived
emission of light by atoms or
molecules that sometimes occurs
after they absorb light
X-rays are detected by their ability
to penetrate matter and expose a
photographic plate
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The Discovery of Radioactivity
• Becquerel discovered that certain minerals were
•
constantly producing energy rays that could
penetrate matter
Becquerel determined that
1. all the minerals that produced these rays contained
uranium
2. the rays were produced even though the mineral was not
exposed to outside energy
• He called them uranic rays because they were
emitted from minerals that contained uranium
 like X-rays
 but not related to phosphorescence
• Energy apparently being produced without
energy input??
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The Curies
• Marie Curie broke down these
minerals and used an electroscope to
detect where the uranic rays were
coming from
• She discovered the rays were
emitted from specific elements
• She also discovered new elements
by detecting their rays
 radium named for its green
phosphorescence
 polonium named for her homeland
• Because these rays were no longer
just a property of uranium, she
renamed it radioactivity
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Electroscope
When charged, the metal
foils spread apart due to
like charge repulsion
When exposed to
ionizing radiation, the
radiation knocks
electrons off the
air molecules, which
jump onto the foils
and discharge them,
allowing them to
drop down
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Other Properties of Radioactivity
• Radioactive rays can ionize matter
cause uncharged matter to become charged
basis of Geiger Counter and electroscope
• Radioactive rays have high energy
• Radioactive rays can penetrate matter
• Radioactive rays cause phosphorescent
chemicals to glow
basis of scintillation counter
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What Is Radioactivity?
• Radioactivity is the release of tiny, high•
energy particles or gamma rays from an
atom
Particles are ejected from the nucleus
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Types of Radioactive Decay
• Rutherford discovered three types of rays
 alpha (a) rays
have a charge of +2 c.u. and a mass of 4 amu
what we now know to be helium nucleus
 beta (b) rays
have a charge of −1 c.u. and negligible mass
electron-like
 gamma (g) rays
form of light energy (not a particle like a and b)
• In addition, some unstable nuclei emit positrons
 like a positively charged electron
• Some unstable nuclei will undergo electron
capture
 a low energy electron is pulled into the nucleus
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Rutherford’s Experiment
++++++++++++
g
b
a
--------------
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Penetrating Ability of Radioactive Rays
a
g
b
0.01 mm
1 mm
100 mm
Pieces of Lead
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Facts About the Nucleus
• Very small volume compared to volume of
•
•
•
the atom
Essentially entire mass of atom
Very dense
Composed of protons and neutrons that are
tightly held together
the particles that make up the nucleus are called
nucleons
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Facts About the Nucleus
• Every atom of an element has the same number
of protons
atomic number (Z)
• Atoms of the same elements can have different
numbers of neutrons
isotopes
different atomic masses
• Isotopes are identified by their mass number (A)
mass number = number of protons + neutrons
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Facts About the Nucleus
• The number of neutrons is calculated by
subtracting the atomic number from the
mass number
• The nucleus of an isotope is called a
nuclide
less than 10% of the known nuclides are nonradioactive, most are radionuclides
• Each nuclide is identified by a symbol
Element – Mass Number = X – A
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Radioactivity
• Radioactive nuclei spontaneously decompose into
smaller nuclei
 radioactive decay
 we say that radioactive nuclei are unstable
 decomposing involves the nuclide emitting a particle
and/or energy
• The parent nuclide is the nucleus that is
•
•
undergoing radioactive decay
The daughter nuclide is the new nucleus that is
made
All nuclides with 84 or more protons are radioactive
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Important Atomic Symbols
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Transmutation
• Rutherford discovered that during the radioactive
process, atoms of one element are changed into
atoms of a different element – transmutation
 showing that statement 3 of Dalton’s Atomic Theory is not
valid all the time, only for chemical reactions
• For one element to change into another, the
number of protons in the nucleus must change!
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Chemical Processes vs.
Nuclear Processes
• Chemical reactions involve changes in the
electronic structure of the atom
atoms gain, lose, or share electrons
no change in the nuclei occurs
• Nuclear reactions involve changes in the
structure of the nucleus
when the number of protons in the nucleus
changes, the atom becomes a different element
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Nuclear Equations
• We describe nuclear processes with nuclear
•
•
equations
Use the symbol of the nuclide to represent the
nucleus
Atomic numbers and mass numbers are conserved
 use this fact to predict the daughter nuclide if you know
parent and emitted particle
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Alpha Emission
• An a particle contains 2 protons
and 2 neutrons
helium nucleus
• Most ionizing, but least
•
penetrating of the types of
radioactivity
Loss of an alpha particle means
atomic number decreases by 2
mass number decreases by 4
222
88
Ra  He 
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2
20
218
86
Rn
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Beta Emission
• A b particle is like an electron
moving much faster
produced from the nucleus
• About 10 times more penetrating than a, but
•
only about half the ionizing ability
When an atom loses a b particle its
atomic number increases by 1
mass number remains the same
• In beta decay, a neutron changes into a proton
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Gamma Emission
• Gamma (g) rays are high energy photons of
•
•
light
No loss of particles from the nucleus
No change in the composition of the nucleus
 same atomic number and mass number
• Least ionizing, but most penetrating
• Generally occurs after the nucleus undergoes
some other type of decay and the remaining
particles rearrange
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Positron Emission
• Positron has a charge of +1 c.u. and
negligible mass
anti-electron
• Similar to beta particles in their ionizing and
•
penetrating ability
When an atom loses a positron from the
nucleus, its
mass number remains the same
atomic number decreases by 1
• Positrons result from a proton changing into
a neutron
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Electron Capture
• Occurs when an inner orbital electron is pulled
•
into the nucleus
No particle emission, but atom changes
same result as positron emission
• Proton combines with the electron to make a
neutron
mass number stays the same
atomic number decreases by one
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Particle Changes
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What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?
11 p+
9 n0
?
+
= proton
= neutron
Alpha emission giving a daughter nuclide with
nine protons and seven neutrons
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What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?,
Continued
?
9 p+
12 n0
+
= proton
= neutron
= electron
Beta emission giving a daughter nuclide with
10 protons and 11 neutrons
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What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?,
Continued
5 p+
4 n0
?
+
= proton
= neutron
= positron
Positron emission giving a daughter nuclide with
four protons and five neutrons
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Nuclear Equations
• In the nuclear equation, mass numbers
•
and atomic numbers are conserved
We can use this fact to determine the
identity of a daughter nuclide if we know
the parent and mode of decay
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Example 19.2b: Write the nuclear
equation for positron emission from K–40
1. Write the nuclide symbols for both the starting
radionuclide and the particle
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Examle 19.2b: Write the nuclear
equation for positron emission from K–40
2. Set up the equation
•
•
emitted particles are products
captured particles are reactants
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Example 19.2b: Write the nuclear
equation for positron emission from K–40
3. Determine the mass number and atomic
number of the missing nuclide
•
mass and atomic numbers are conserved
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Example 19.2b: Write the nuclear
equation for positron emission from K–40
4. Identify and determine the symbol of the
element from the atomic number
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Practice – Write a nuclear equation for
each of the following
alpha emission from U–238
beta emission from Ne–24
positron emission from N–13
electron capture by Be–7
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What Causes Nuclei to Decompose?
• The particles in the nucleus are held together
by a very strong attractive force only found in
the nucleus called the strong force
acts only over very short distances
• The neutrons play an important role in
stabilizing the nucleus, as they add to the
strong force, but don’t repel each other like the
protons do
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N/Z Ratio
• The ratio of neutrons : protons is an important
•
•
measure of the stability of the nucleus
If the N/Z ratio is too high, neutrons are
converted to protons via b decay
If the N/Z ratio is too low, protons are
converted to neutrons via positron emission or
electron capture
or via a decay – though not as efficiently
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Valley of Stability
for Z = 1  20,
stable N/Z ≈ 1
for Z = 20  40,
stable N/Z approaches 1.25
for Z = 40  80,
stable N/Z approaches 1.5
for Z > 83,
there are no stable nuclei
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Example 19.3b: Predict the kind of radioactive
decay that Mg−22 undergoes
• Mg–22
 Z = 12
 N = 22 – 12 = 10
• N/Z = 10/12 = 0.83
• From Z = 1  20, stable
•
nuclei have N/Z ≈ 1
Because Mg–22 N/Z is
low, it should convert p+
into n0, therefore it will
undergo positron
emission or electron
capture
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Practice – Predict whether Kr–85 is stable or
radioactive. If radioactive, predict the mode of
radioactive decay and the daughter nuclide.
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Practice – Predict whether Kr–85 is stable or
radioactive. If radioactive, predict the mode of
radioactive decay and the daughter nuclide.
Kr–85 has Z = 36 and N = (85 − 36) = 49
Because most stable isotopes with Z between 20 and 40 have
N/Z ratios between 1 and 1.25, we expect Kr–85 to be
radioactive
Because the N/Z ratio of Kr–85 is greater than 1.25, it has
too many neutrons and will undergo b decay to reduce them
(Kr–85 is a byproduct of nuclear fission and was released into the atmosphere
when atom bombs were tested in the 1940’s to 1960’s)
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Magic Numbers
• Besides the N/Z ratio, the actual numbers of protons and
•
•
•
neutrons affects stability
Most stable nuclei have even numbers of protons and
neutrons
Only a few have odd numbers of protons and neutrons
If the total number of nucleons adds to a magic number,
the nucleus is more stable
 same principle as stability of the
noble gas electron configuration
 most stable when N or Z = 2, 8,
20, 28, 50, 82; or N = 126
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Decay Series
• In nature, often one radioactive nuclide
changes into another radioactive nuclide
 i.e. the daughter nuclide is also radioactive
• All of the radioactive nuclides that are
•
produced one after the other until a stable
nuclide is made is called a decay series
To determine the stable nuclide at the end of
the series without writing it all out
1. count the number of a and b decays
2. from the mass no. subtract 4 for each a decay
3. from the atomic no. subtract 2 for each a decay
and add 1 for each b
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U-238
Decay Series
a
b
b
a
a
a
a
b
a
b
a
b
b
a
or
a
b
a
b
b
a
b
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or other
combinations
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Detecting Radioactivity
To detect something, you need to identify what it does
• Radioactive rays can expose light-protected
photographic film
• We may use photographic film to detect the
presence of radioactive rays – film badge
dosimeters
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Detecting Radioactivity
• Radioactive rays cause air to become ionized
• An electroscope detects radiation by its ability
to penetrate the flask and ionize the air inside
• A Geiger-Müller counter works by counting
electrons generated when Ar gas atoms are
ionized by radioactive rays
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Detecting Radioactivity
• Radioactive rays cause certain chemicals to
•
give off a flash of light when they strike the
chemical
A scintillation counter is able to count the
number of flashes per minute
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Natural Radioactivity
• There are small amounts of radioactive
•
•
minerals in the air, ground, and water
Even in the food you eat!
The radiation you are exposed to from natural
sources is called background radiation
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Rate of Radioactive Decay
• It was discovered that the rate of change in the
amount of radioactivity was constant, and
different for each radioactive “isotope”
change in radioactivity measured with Geiger counter
counts per minute
• Each radionuclide had a particular length of time
it required to lose half its radioactivity
a constant half-life
we know that processes with a constant half-life follow
first order kinetic rate laws
• The rate of radioactive change was not affected
by temperature
meaning radioactivity is not a chemical reaction!
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Kinetics of Radioactive Decay
• Rate = kN
N = number of radioactive nuclei
• t1/2 = 0.693/k
• the shorter the half-life, the more nuclei decay
every second – we say the sample is hotter
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Half-Lives of Various Nuclides
Half-Life
Type of
Decay
Th–232
1.4 x 1010 yr
alpha
U–238
4.5 x 109 yr
alpha
C–14
5730 yr
beta
Rn–220
55.6 sec
alpha
Th–219
1.05 x 10–6 sec
alpha
Nuclide
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Half-Life
Half of the radioactive atoms decay each half-life
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Pattern for Radioactive Decay
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Example19.4: If you have a 1.35 mg sample of Pu–236,
calculate the mass that will remain after 5.00 years
Given:
Find:
Conceptual
Plan:
Relationships:
mass Pu–236 = 1.35 mg, t = 5.00 yr, t1/2 = 2.86 yr
mass remaining, mg
t1/2
k
+
m 0, t
mt
Solve:
Check: units are correct, the magnitude makes because since it is
less than ½ the original mass for longer than 1 half-life
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Practice—Radon–222 is a gas that is suspected of
causing lung cancer as it leaks into houses. It is
produced by uranium decay. Assuming no loss or gain
from leakage, if there is 10.24 g of Rn–222 in the house
today, how much will there be in 5.4 weeks?
( Rn–222 half-life is 3.8 Days)
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Practice – If there is 10.24 g of Rn–222 in the house
today, how much will there be in 5.4 weeks?
Given:
Find:
Conceptual
Plan:
Relationships:
mass Rn–222 = 10.24 g, t = 5.4 wks, t1/2 = 3.8 d
mass remaining, g
t1/2
k
+
m 0, t
mt
Solve:
Check: units are correct, the magnitude makes sense because the
length of time is 10 half-lives
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Radiometric Dating
• The change in the amount of radioactivity of a
•
particular radionuclide is predictable and not
affected by environmental factors
By measuring and comparing the amount of a
parent radioactive isotope and its stable
daughter we can determine the age of the
object
by using the half-life and the previous equations
• Mineral (geological) dating
compare the amount of U-238 to Pb-206 in volcanic
rocks and meteorites
dates the Earth to between 4.0 and 4.5 billion yrs. old
compare amount of K-40 to Ar-40
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Radiocarbon Dating
• All things that are alive or were once alive
•
contain carbon
Three isotopes of carbon exist in nature, one of
which, C–14, is radioactive
C–14 radioactive with half-life = 5730 yrs
• We would normally expect a radioisotope with
this relatively short half-life to have disappeared
long ago, but atmospheric chemistry keeps
producing C–14 at nearly the same rate it
decays
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Radiocarbon Dating
• While still living, C–14/C–12 is constant because
the organism replenishes its supply of carbon
CO2 in air ultimate source of all C in organism
• Once the organism dies the C–14/C–12 ratio
•
•
decreases
By measuring the C–14/C–12 ratio in a once
living artifact and comparing it to the C–14/C–12
ratio in a living organism, we can tell how long
ago the organism was alive
The limit for this technique is 50,000 years old
about 9 half-lives, after which radioactivity from C–14
will be below the background radiation
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Radiocarbon Dating
% C-14 (compared to living
organism)
Object’s Age (in years)
100%
0
90%
870
80%
1850
60%
4220
50%
5730
40%
7580
25%
11,500
10%
19,000
5%
24,800
1%
38,100
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Example 19.5: An ancient skull gives 4.50 dis/min∙gC. If a
living organism gives 15.3 dis/min∙gC, how old is the skull?
Given: ratet1/2 = 4.50 dis/min∙gC, ratet1/2 = 15.3 dis/min∙gC
Find: time, yr
Conceptual
Plan:
Relationships:
t1/2
k
+ rate0, ratet
t
Solve:
Check: units are correct, the magnitude makes sense
because it is less than 2 half-lives
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Practice – Archeologists have dated a civilization to
15,600 yrs ago. If a living sample gives 20.0 counts per
minute per gram C, what would be the number of counts
per minute per gram C for a rice grain found at the site?
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Practice – What would be the number of counts per
minute per gram for a rice grain found at the site?
Given: t = 15,600 yr, rate0 = 20.0 counts/min∙gC
Find: ratet, counts/min∙gC
Conceptual
Plan:
Relationships:
t1/2
k
+
rate0, t
ratet
Solve:
Check: units are correct, the magnitude makes sense because
it is between 10 and 25% of the original activity
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Nonradioactive Nuclear Changes
• A few nuclei are so unstable that if
•
•
their nucleus is hit just right by a
neutron, the large nucleus splits
into two smaller nuclei — this is
called fission
Small nuclei can be accelerated to
such a degree that they overcome
their charge repulsion and smash
together to make a larger nucleus this is called fusion
Both fission and fusion release
enormous amounts of energy
Lise Meitner
 fusion releases more energy per gram
than fission
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Fission Chain Reaction
• A chain reaction occurs when a reactant in the
process is also a product of the process
in the fission process it is the neutrons
so you only need a small amount of neutrons to start
the chain
• Many of the neutrons produced in fission are
either ejected from the uranium before they hit
another U-235 or are absorbed by the
surrounding U-238
• Minimum amount of fissionable isotope needed
to sustain the chain reaction is called the
critical mass
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Fissionable Material
• Fissionable isotopes include U–235, Pu–239,
•
and Pu–240
Natural uranium is less than 1% U–235
rest mostly U–238
not enough U–235 to sustain chain reaction
• To produce fissionable uranium, the natural
uranium must be enriched in U–235
to about 7% for “weapons grade”
to about 3% for reactor grade
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Nuclear Power
• Nuclear reactors use fission to generate
electricity
about 20% of U.S. electricity
uses the fission of U–235 to produce heat
• The heat boils water, turning it to steam
• The steam turns a turbine, generating
electricity
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Nuclear Power Plants vs.
Coal-Burning Power Plants
• Use about 2 million kg
• Use about 50 kg of
•
fuel to generate
enough electricity for 1
million people
No air pollution
•
•
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of fuel to generate
enough electricity for 1
million people
Produce NO2 and SOx
that add to acid rain
Produce CO2 that
adds to the
greenhouse effect
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Nuclear Power Plants - Core
• The fissionable material is stored in long tubes,
called fuel rods, arranged in a matrix
subcritical
• Between the fuel rods are control rods made
of neutron-absorbing material
B and/or Cd
neutrons needed to sustain the chain reaction
• The rods are placed in a material to slow down
the ejected neutrons, called a moderator
allows chain reaction to occur below critical mass
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Pressurized Light Water Reactor
• Design used in United States (GE,
•
•
•
Westinghouse)
Water is both the coolant and moderator
Water in core kept under pressure to keep it
from boiling
Fuel is enriched uranium
subcritical
• Containment dome of concrete
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Containment
Building
PLWR
Turbine
Condenser
Boiler
Core
Cold
Water
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PLWR - Core
The control rods
are made of
neutron absorbing
material. This
allows the rate of
Control
neutron flow
Rods
through the
reactor to be
controlled. Because
the neutrons are
required to
continue the chain
reaction, the
control rods
control the rate of
nuclear fission
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Hot
Water
Fuel
Rods
Cold
Water
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Concerns about Nuclear Power
• Core melt-down
 water loss from core, heat melts core
 China Syndrome
 Chernobyl
• Waste disposal
 waste highly radioactive
 reprocessing, underground storage?
 Federal High Level Radioactive Waste
Storage Facility at Yucca Mountain, Nevada
• Transporting waste
• How do we deal with nuclear power
plants that are no longer safe to
operate?
 Yankee Rowe in Massachusetts
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Where Does the Energy from
Fission Come from?
• During nuclear fission, some of the mass of the
nucleus is converted into energy
E = mc2
• Each mole of U–235 that fissions produces
about 1.7 x 1013 J of energy
a very exothermic chemical reaction produces 106 J
per mole
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Mass Defect and
Binding Energy
• When a nucleus forms, some of the mass of the
•
•
separate nucleons is converted into energy
The difference in mass between the separate
nucleons and the combined nucleus is called the
mass defect
The energy that is released when the nucleus
forms is called the binding energy
 1 MeV = 1.602 x 10−13 J
 1 amu of mass defect = 931.5 MeV
 the greater the binding energy per nucleon, the more
stable the nucleus is
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Example19.7: Calculate the mass defect and nuclear binding
energy per nucleon (in MeV) for C–16, a radioactive isotope of
carbon with a mass of 16.014701 amu
Given: mass C-16 = 16.01470 amu, mass p+ = 1.00783 amu,
mass n0 = 1.00866 amu
Find: mass defect in amu, binding energy per nucleon in MeV
Conceptual
Plan:
mp+, mn0, mC-16
mass
defect
binding energy
Relationships:
Solve:
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Practice – Calculate the binding energy per
nucleon in Fe–56
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Practice – Calculate the binding energy per nucleon
in Fe–56 (mass 55.93494 amu)
Given: mass Fe-56 = 55.93494 amu, mass p+ = 1.00783 amu,
mass n0 = 1.00866 amu
Find: binding energy per nucleon in MeV
mass
Conceptual m , m , m
binding energy
p+
n0
C-16
defect
Plan:
Relationships:
Solve:
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Nuclear Fusion
• Fusion is the combining of light nuclei to make a
•
•
heavier, more stable nuclide
The Sun uses the fusion of hydrogen isotopes to
make helium as a power source
Requires high input of energy to initiate the
process
 because need to overcome repulsion of positive nuclei
• Produces 10x the energy per gram as fission
• No radioactive byproducts
• Unfortunately, the only currently working
application is the H-bomb
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Fusion
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Tokamak Fusion Reactor
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Making New Elements:
Artificial Transmutation
• High energy particles can be smashed into
target nuclei, resulting in the production of new
nuclei
• The particles may be radiation from another
radionuclide, or charged particles that are
accelerated
 Rutherford made O–17 bombarding N–14 with alpha
rays from radium
 Cf–244 is made by bombarding U–238 with C–12 in
a particle accelerator
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Artificial Transmutation
• Bombardment of one nucleus with another
causing new atoms to be made
can also bombard with neutrons
• Reaction done in a particle accelerator
linear
cyclotron
Tc-97 is made by bombarding Mo-96 with
deuterium, releasing a neutron
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Linear Accelerator
+- +
- +- +
- +- +
- +- +
- +- +
- +- +
- +- +
- +- +
- +- +
- +- +
- +- +
- ++
+
+
source
Nuclear Chemsity
target
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Cyclotron
target
source
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Practice – Predict the other daughter nuclide
and write a nuclear equation for each of the
following
bombarding Ni–60 with a proton to make Co–57
bombarding N–14 with a neutron to make C–12
bombarding Cf–250 with B–11 producing 4 neutrons
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Practice – Predict the other daughter nuclide
and write a nuclear equation for each of the
following
bombarding Ni–60 with a proton to make Co–57
bombarding N–14 with a neutron to make C–12
bombarding Cf–250 with B–11 producing 4 neutrons
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Biological Effects of Radiation
• Radiation has high energy, energy enough to
knock electrons from molecules and break
bonds
ionizing radiation
• Energy transferred to cells can damage
biological molecules and cause malfunction of
the cell
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Acute Effects of Radiation
• High levels of radiation over a short period of
time kill large numbers of cells
from a nuclear blast or exposed reactor core
• Causes weakened immune system and lower
ability to absorb nutrients from food
may result in death, usually from infection
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Chronic Effects
• Low doses of radiation over a period of time
show an increased risk for the development of
cancer
radiation damages DNA that may not get repaired
properly
• Low doses over time may damage
•
reproductive organs, which may lead to
sterilization
Damage to reproductive cells may lead to
genetic defects in offspring
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Measuring Radiation Exposure
• The curie (Ci) is an exposure of 3.7 x 1010 events per
second
 no matter the kind of radiation
• The gray (Gy) measures the amount of energy absorbed
by body tissue from radiation
 1 Gy = 1 J/kg body tissue
• The rad also measures the amount of energy absorbed by
body tissue from radiation
 1 rad = 0.01 Gy
• A correction factor is used to account for a number of
factors that affect the result of the exposure – this
biological effectiveness factor is the RBE, and the result is
the dose in rems
 rads x RBE = rems
 rem = roentgen equivalent man
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Factors that Determine the
Biological Effects of Radiation
1. The more energy the radiation has, the larger its effect
can be
2. The better the ionizing radiation penetrates human
tissue, the deeper effect it can have
 Gamma >> Beta > Alpha
3. The more ionizing the radiation, the larger the effect of
the radiation
 Alpha > Beta > Gamma
4. The radioactive half-life of the radionuclide
5. The biological half-life of the element
6. The physical state of the radioactive material
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Biological Effects of Radiation
• The amount of danger to humans of
radiation is measured in the unit rems
Dose
(rems)
20-100
100-400
500+
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Probable Outcome
decreased white blood cell count;
possible increased cancer risk
radiation sickness;
increased cancer risk
death
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Medical Uses of Radioisotopes,
Diagnosis
• Radiotracers
certain organs absorb most or all of a particular
element
you can measure the amount absorbed by using
tagged isotopes of the element and a Geiger
counter
tagged = radioisotope that can then be detected
and measured
use radioisotope with a short half-life
use radioisotope that is low ionizing
beta or gamma
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Bone Scans
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Medical Uses of Radioisotopes,
Diagnosis
• PET scan
positron emission tomography
F–18 tagged glucose
F–18 is a positron emitter
brain scan and function
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Medical Uses of Radioisotopes,
Treatment – Radiotherapy
• Cancer treatment
 cancer cells more sensitive to radiation than healthy
cells – use radiation to kill cancer cells without doing
significant damage
 brachytherapy
 place radioisotope directly at site of cancer
 teletherapy
 use gamma radiation from Co–60 outside to penetrate inside
 IMRT
 radiopharmaceutical therapy
 use radioisotopes that concentrate in one area of the body
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Gamma Ray Treatment
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Nonmedical Uses of
Radioactive Isotopes
• Smoke detectors
 Am–241
 smoke blocks ionized air, breaks
circuit
• Insect control
 sterilize males
• Food preservation
• Radioactive tracers
 follow progress of a “tagged”
atom in a reaction
• Chemical analysis
 neutron activation analysis
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Nonmedical Uses of
Radioactive Isotopes
• Authenticating art object
 many older pigments and ceramics were made
from minerals with small amounts of radioisotopes
• Crime scene investigation
• Measure thickness or condition of industrial
materials
 corrosion
 track flow through process
 gauges in high temp processes
 weld defects in pipelines
 road thickness
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Nonmedical Uses of
Radioactive Isotopes
• Agribusiness
 develop disease-resistant crops
 trace fertilizer use
• Treat computer disks to enhance data integrity
• Nonstick pan coatings
 initiates polymerization
• Photocopiers to help keep paper from jamming
• Sterilize cosmetics, hair products and contact lens
solutions and other personal hygiene products
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