Transcript ch 25 power point 08-09

Ch. 25- Nuclear Chemistry
Diablo Canyon
Nuclear Power Plant
San Luis Obispo, CA
(192 miles south of
Cupertino)
Marvel Comics’ “The
Incredible Hulk” was
created in 1962 by Stan Lee
and artist Jack Kirby. The
Hulk’s powers began when
nuclear scientist Dr. Bruce
Banner was accidentally
bombarded with gamma
rays from a "gamma bomb"
he had invented.
(originally ch. 18 from old textbook)
25.1 Nuclear
Radiation
25.2 Nuclear
Transformations
25.3 Fission and
Fusion of Atomic
Nuclei
25.4 Radiation in Your
Life
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1
Atomic Review
• Atomic number = # of p+
– Every atom of an element has the same atomic
number because the # p defines the element.
• Mass number (or atomic mass) = sum of p+ & n
The # n may vary without changing the element.
• Atomic notation: Mass #
Atomic #
X
Symbol
25
Ex: magnesium atom with 13 n = Mg
12
2
Practice
Fill in the blanks:
Name
Hydrogen-1
Helium-5
Carbon-13
Symbol
1
H
1
5
He
2
13
C
6
#p
#n
1
0
2
3
6
7
3
Four Forces in the Nucleus
Repulsive:
1. Electrostatic: between p+
(like charges repel)
+
+
Attractive:
2. “Strong force”: between p+
3. “Weak force”: between p+ and n
4. Gravity: between all particles
Strong > electrostatic > weak > gravity
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25.1 Nuclear Radiation
Marie Curie was a Polish
scientist whose research led to
many discoveries about
radiation and radioactive
elements. In 1934 she died
from leukemia caused by her
long-term exposure to
radiation. You will learn about
the various types of radiation
and their effects.
Natural Radioactivity
* Discovered in 1895 by Antoine Henri Becquerel, who
observed that a uranium salt produced an image on
photographic film.
* The term radioactivity was coined in 1898 by Marie Curie, a
Polish physicist, who was doing research with her husband
Pierre. (They did much of the initial work on radioactivity,
and eventually died of radiation-related illnesses.)
Radioactivity: spontaneous emission of particles and/or
energy from the nucleus of an atom
Radioactive decay: process in which a radioactive atom
disintegrates into a different element
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Radioactivity
How does an unstable nucleus release energy?
• Marie Curie (1867-1934) and Pierre Curie
(1859-1906) were able to show that rays
emitted by uranium atoms caused fogging
in photographic plates.
–Marie Curie named the process by which
materials give off such rays
radioactivity.
–The penetrating rays and particles
emitted by a radioactive source are
called radiation.
25.1
Radioactivity
Nuclear reactions differ from chemical
reactions in a number of important ways.
• In chemical reactions, atoms tend to attain
stable electron configurations by losing or
sharing electrons.
• In nuclear reactions, the nuclei of unstable
isotopes, called radioisotopes, gain stability
by undergoing changes.
• An unstable nucleus releases energy by
emitting radiation during the process of
radioactive decay.
25.1
Types of Radiation
The three main types of nuclear radiation are alpha
radiation, beta radiation, and gamma radiation.
Types of Radioactive Decay
Type
alpha
a
beta
Consists of
Stopped by Interesting Fact
He nucleus:
2p&2n
Paper or
skin
If ingested, is
harmful to lungs
High energy e-
Clothing,
glasses, or
thin sheet
of Al
Causes damage
to sensitive
tissues like eyes
A few feet
of dirt or
concrete,
or 6” of Pb
Causes severe
damage to body
tissues
b
gamma Photon (particle of
light)
g
* Has essentially no
mass (m < 5.81 x 10-72
g…its complicated!)
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Alpha decay
Example:
240
Pu
94
236
U
92
+
4
2
He
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Alpha decay
Example:
240
Pu
94
236
U
92
+
4
2
He
12
Beta decay
• Ex:
137
Cs
55
1
n
0
137
0
Ba
+
56
-1
1
0
p
1
+
-1
(One of Cs’s neutrons converts to a proton and electron.)
e
e
Beta decay animation: http://ie.lbl.gov/education/glossary/AnimatedDecays/Beta-Decay.html 13
14
Gamma ray emission
• Ex: Pu* (energized) → Pu (stable)
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25.1
Types of Radiation
Gamma Radiation
A high-energy photon emitted by a radioisotope is called
a gamma ray. The high-energy photons are
electromagnetic radiation.
25.1
Types of Radiation
25.1 Section Quiz.
1. Certain elements are radioactive because their
atoms have
a) more neutrons than electrons.
b) an unstable nucleus.
c) a large nucleus.
d) more neutrons than protons.
25.1 Section Quiz.
2. An unstable nucleus releases energy by
a) emitting radiation.
b) thermal vibrations.
c) a chemical reaction.
d) giving off heat.
25.1 Section Quiz.
3. Which property does NOT describe an alpha
particle?
a) 2+ charge
b) a relatively large mass
c) a negative charge
d) low penetrating power
25.1 Section Quiz.
4. When a radioactive nucleus releases a high-speed
electron, the process can be described as
a) oxidation.
b) alpha emission.
c) beta emission.
d) gamma radiation.
25.2 Nuclear Transformations
Radon-222 is a
radioactive isotope
that is present
naturally in the soil in
some areas. It has a
constant rate of decay.
You will learn about
decay rates of
radioactive substances.
Nuclear Stability and Decay
What determines the type of decay a
radioisotope undergoes?
– The nuclear force is an attractive force that acts between all
nuclear particles that are extremely close together, such as
protons and neutrons in a nucleus
– At these short distances, the nuclear force dominates over
electromagnetic repulsions and hold the nucleus together.
– More than 1,500 different nuclei are known. Of those, only 264
are stable and do not decay or change with time. These nuclei
are in a region called the band of stability.
Nuclear Stability and Decay
25.2
Nuclear Stability and Decay
• The neutron-to-proton
ratio determines the
type of decay that
occurs.
• A positron is a particle
with the mass of an
electron but a positive
charge. During positron
emission, a proton
changes to a neutron.
Unstable Atoms
* Stable, naturally occurring isotopes
• If # of neutrons is too
high or too low, the
nucleus becomes
unstable and emits
energy.
1
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*Transmutation
• Conversion of one element into another that is the result of
radioactive decay.
Artificial transmutation:
• First accomplished by Rutherford in 1919, even though
alchemists tried for hundreds of years.
• Transmutation of lead into gold was achieved by Glenn
Seaborg, who succeeded in transmuting a small quantity of
lead in 1980. He also first isolated plutonium for the atomic
bomb and discovered/”created” many elements. (NY Times,
Feb 1999)
• There is an earlier report (1972) in which Soviet physicists at a
nuclear research facility in Siberia accidentally discovered a
reaction for turning lead into gold when they found the lead
shielding of an experimental reactor had changed to gold.
• Accomplished with particle accelerators
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Transmutation Reactions
What are two ways that transmutation can occur?
The conversion of an atom of one element to an atom of
another element is called transmutation.
– Transmutation can occur by radioactive decay. Transmutation
can also occur when particles bombard the nucleus of an atom.
Transmutation Reactions
The first artificial transmutation reaction involved
bombarding nitrogen gas with alpha particles.
Transmutation Reactions
25.2
The elements in the periodic table with atomic numbers
above 92, the atomic number of uranium, are called the
transuranium elements.
– All transuranium elements undergo transmutation.
– None of the transuranium elements occur in nature, and all of them are
radioactive.
Transuranium elements
are synthesized in nuclear
reactors and nuclear
accelerators.
*Disintegration Series
• “Heavy” atoms (greater than Bismuth, #83) naturally decay to
smaller atoms along a consistent path, or series, of decays.
Atomic Number & Symbol
Mass Number
Radioactive U-238 → Th-234 + a
Th-234 → Pa-234 + b
Pa-234 → U-234 + b
U-234 → Th-230 + a
Th-230 → Ra-226 + a
Ra-226 → Rn-222 + a
Rn-222 → Po-218 + a
Po-218 → Pb-214 + a
Pb-214 → Bi-214 + b
Bi-214 → Po-214 + b
Po-214 → Pb-210 + a
Pb-210 → Bi-210 + b
Bi-210 → Po-210 + b
Po-210 → Stable Pb-206 + a
Source: http://www.frontiernet.net/~jlkeefer/uranium.html
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*Radiocarbon (C-14) dating
• Discovered at University of Chicago in 1949 by Dr.
W.F. Libby and his colleagues.
Basic assumptions:
• CO2 in the atmosphere contains about 0.00000000010% C-14;
this level is held constant through the decay of N-14 to form C14 which happens in the upper atmosphere.
• Plants consume CO2 during photosynthesis and animals eat the
plants, so they contain the same C-14:C-12 ratio as long as
they are alive.
• When an organism dies, the amount of C-12 does not change,
but the C-14 content diminishes as it decays. The half-life of
C-14 is 5668 years.
• By comparing the C-14:C-12 ratio in an artifact to the same
ratio in living plants, the age of the artifact can be estimated.
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• The accuracy of the method has been validated by comparison
testing of artifacts with independently known ages, such as those of
ancient Egypt and old redwood trees.
Limitations:
• C-14 dating has a limit of about 70,000 years. Beyond that, the %
of C-14 remaining is too small to accurately calculate the age.
• However, other radiometric dating methods exist, including:
Rb-87 : Strontium 87 (half-life of 48.8 billion years)
Th-232 : Pb-208 (half-life of 14.0 billion years)
U-238 : Pb-206 (half-life of 4.5 billion years)
K-40 : Ar-40 (half-life of 1.3 billion years)
• The formation of our solar system (and thus the Earth) has been
estimated at 4.5 - 5.0 billion years.
• It is also estimated that our universe is between 15-20 billion years
old.
Sources:
http://www.geology.sdsu.edu/visualgeology/geology101/lab6time.htm
http://www.dc.peachnet.edu/~pgore/geology/geo102/radio.htm
http://superstringtheory.com/cosmo/cosmo1.html
Half-Life
A half-life (t1/2) is the time required for
one-half of the nuclei of a radioisotope
sample to decay to products.
After each half-life, half
of the existing
radioactive atoms have
decayed into atoms of
a new element.
Half Life
Ex:
• Phosphorus-32 radioactively decays to form
Sulfur-32
• Half life
32P
= 14 days
35
Half-Life
The ratio of Carbon-14 to stable carbon
in the remains of an organism changes
in a predictable way that enables the
archaeologist to obtain an estimate of
its age.
25.2 Section Quiz.
1. During nuclear decay, if the atomic number
decreases by one but the mass number is
unchanged, the radiation emitted is
a) a positron.
b) an alpha particle.
c) a neutron.
d) a proton.
25.2 Section Quiz.
2. When potassium-40 (atomic number 19)
decays into calcium-40 (atomic number 20),
the process can be described as
a) positron emission.
b) alpha emission.
c) beta emission.
d) electron capture.
25.2 Section Quiz.
3. If there were 128 grams of radioactive
material initially, what mass remains after
four half-lives?
a) 4 grams
b) 32 grams
c) 16 grams
d) 8 grams
25.2 Section Quiz.
4. When transmutation occurs, the ________
always changes.
a) number of electrons
b) mass number
c) atomic number
d) number of neutrons
25.2 Section Quiz
5. Transmutation occurs by radioactive decay
and also by
a) extreme heating.
b) chemical reaction.
c) high intensity electrical discharge.
d) particle bombardment of the nucleus.
25.3 Fission and Fusion of Atomic Nuclei
The sun is not actually
burning. If the energy given
off by the sun were the
product of a combustion
reaction, the sun would
have burned out
approximately 2000 years
after it was formed, long
before today. You will learn
how energy is produced in
the sun.
25.3
Nuclear Fission
What happens in a nuclear chain reaction?
When the nuclei of certain isotopes are bombarded with
neutrons, they undergo fission, the splitting of a nucleus into
smaller fragments.
In a chain reaction, some of the neutrons produced react with
other fissionable atoms, producing more neutrons which react
with still more fissionable atoms.
Nuclear Fission
• Fission: process in which the nucleus of a large, radioactive
atom splits into 2 or more smaller nuclei
– Caused by a collision with an energetic neutron.
139 Ba + 94 Kr + 3 1n + energy
1 n + 235 U
56
36
0
0
92
• *A neutron is absorbed by a U-235 nucleus. The nucleus is
now less stable than before. It then splits into 2 parts and
energy is released. Several neutrons are also produced; they
may go on to strike the nuclei of other atoms causing further
fissions in a process called supercriticality.
Fission animation: http://www.howstuffworks.com/nuclear-bomb3.htm
44
• *The process of neutron capture and nucleus splitting
happens very quickly (takes about 1 x 10-12 seconds).
• An incredible amount of energy is released:
– As heat and gamma radiation
– Because the product atoms and neutrons weigh
less than the original U-235 atom; the “missing
mass“ has been converted to energy by E=mc2
45
Mass-Energy Relationship
• Einstein's theory of relativity states that energy and
mass are related by the speed of light (c) squared.
E = mc2
• Can be used to calculate the energy liberated when
the “missing mass” (between reactants & products) is
known.
• * The energy that can be released from 2 kg of highly
enriched U-235 (as used in a nuclear bomb) is
roughly equal to the combustion of a million gallons
of gasoline. 2 kg of U-235 is smaller than a baseball;
a million gallons of gasoline would fill approximately
220 tanker trucks.
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Nuclear Fission
A Nuclear Power Plant
Neutron absorption is a
process that decreases the
number of slow-moving
neutrons. Control rods, made
of a material such a cadmium,
are used to absorb neutrons.
Neutron moderation is a
process that slows down
neutrons so the reactor fuel
(uranium-235 or plutonium239) captures them to
continue the chain reaction.
*Harnessing Fission: A nuclear power plant
Check out: http://science.howstuffworks.com/nuclear-power1.htm
• Nuclear power plants utilize the energy released in a controlled fission
reaction in the core to heat water in one pipe.
• The heat then vaporizes water in another pipe.
• The steam drives a turbine and generates electricity.
• The steam is in a
closed circuit that is
never exposed any
radiation.
•The speed of the
fission chain reaction is
regulated using carbon
control rods which can
absorb extra neutrons.
25.3
Nuclear Waste
Why are spent fuel rods from a nuclear reaction
stored in water?
– Water cools the spent rods, and also acts as a radiation
shield to reduce the radiation levels.
*Nuclear Power
• The United States currently imports over 58%
of its oil supply. There is a need to develop
alternative energy sources, such as nuclear,
wind, geothermal, solar, …
• By 2020 it is expected to be 67%.
• At present about 20% of the electrical energy
used in the U.S. is generated from power
plants using uranium. In France the
percentage is 75% .
50
*Nuclear Reactor Operation
Hazards
1. Radioactive waste from normal operations.
2. Reactor coolant has tritium 1H3 which is radioactive with a
half-life of 12.3 years.
3. Used fuel cells are radioactive and have half-lifes in the
millions of years.
4. Miscellaneous equipment can be contaminated with radioactive
material.
Accidents: loss of coolant, coolant flow, or pressure, control rod
drive mechanism failure
• Fuel cell meltdown then liquid uranium pools into a
supercritical mass then explosion then radioactive waste is
ejected around the planet
51
The Atomic Bomb
• Uses an unregulated fission reaction in a very
fast chain reaction that releases a tremendous
amount of energy.
*Critical mass: the minimum amount of
radioactive, fissionable material needed to
create a sustainable fission chain reaction
* Site of fission reaches temperatures believed to
be about 10,000,000°C.
• Produces shock waves and a, b, g, x-rays, and
UV radiation.
52
*A Fission Chain Reaction
*The classic “mushroom cloud” is a result of dust and
debris lifted into the air as a result of the detonation.
*US Army aerial photograph from 80 km away, taken about 1
hour after detonation over Nagasaki, Japan, August 9, 1945.
Nuclear Fusion
Fusion: process in which 2 nuclei of small elements are united to
form one heavier nucleus
•
* Requires temperatures on the order of tens of millions of
degrees for initiation.
•
* The mass difference between the small atoms and the
heavier product atom is liberated in the form of energy.
•
Responsible for the tremendous energy output of stars (like
our sun) and the devastating power of the hydrogen bomb.
3H
1
+ 2H
1
4 He + 1 n + energy
2
0
55
*Stars & the Hydrogen Bomb
• The first thermonuclear bomb was exploded in 1952 in the
Marshall islands by the United States; the second was
exploded by Russia (then the USSR) in 1953.
• “H bombs” utilize a fission bomb to ignite a fusion reaction.
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Nuclear Fusion
Fusion occurs when nuclei combine to produce a
nucleus of greater mass. In solar fusion, hydrogen nuclei
(protons) fuse to make helium nuclei and two positrons.
•Fusion reactions, in which small nuclei combine, release much more
energy than fission reactions, in which large nuclei split.
•The use of controlled fusion as an energy source on Earth is appealing.
•The potential fuels are inexpensive and readily available.
•The problems with fusion lie in achieving the high temperatures
necessary to start the reaction and in containing the reaction once it has
started.
25.3 Section Quiz.
1. One of the control mechanisms for a
sustainable nuclear chain reactor involves
slowing down the released neutrons so they
may be captured by other nuclei. This is done
using
a) moderators.
b) shielding.
c) absorbers.
d) control rods.
25.3 Section Quiz.
2. Spent fuel rods are stored in
a) lead-lined containers.
b) deep pools of water.
c) thick concrete bunkers.
d) cadmium or graphite containers.
25.3 Section Quiz.
3. Choose the correct words for the spaces. In
solar fusion, _______ nuclei fuse to form
_______ nuclei.
a) helium, hydrogen
b) hydrogen-1, hydrogen-2
c) hydrogen, helium
d) hydrogen-1, hydrogen-3
25.4 Radiation in Your Life
In a smoke detector, radiation
from the Americum nuclei
ionizes the nitrogen and oxygen
in smoke-free air, allowing a
current to flow. When smoke
particles get in the way, a drop
in current is detected by an
electronic circuit, causing it to
sound an alarm. You will learn
about some of the other
practical uses of radiation.
*Measurement of Radioactivity
Ionizing radiation:
•
•
When radiation from radioactive sources strikes an
atom or a molecule, one or more electrons are
knocked off and an ion is created.
Measured with a Geiger counter, a film badge or a
scintillation counter.
Units:
•
Curie: measures radioactivity emitted by a
radionuclide.
•
Roentgen or rad: measures exposure to gamma
rays or X-rays
•
Rem: accounts for degree of biological effect caused
by the type of radiation exposure.
62
Detecting Radiation
What are three devices used to detect radiation?
• Ionizing radiation is radiation with enough energy to
knock electrons off some atoms of the bombarded
substance to produce ions.
– Devices such as Geiger counters, scintillation counters, and film
badges are commonly used to detect radiation.
Radiation can produce ions,
which can then be detected,
or it can expose a
photographic plate and
produce images.
25.4
Detecting Radiation
A film badge consists of
several layers of photographic
A Geiger counter uses a gasfilm covered with black
filled metal tube to detect
lightproof paper, all encased in a
radiation.
plastic or metal holder.
A scintillation counter
uses a phosphor-coated
surface to detect
radiation.
*Biological Effects of Radiation
Acute:
• High level radiation (gamma ray & x–ray) can cause death.
• Damage is centered in nuclei of cells; cells undergoing rapid cell division are
most susceptible.
• Gamma rays from a Co-60 source are often used to treat cancer (since
cancer cells multiply rapidly).
Long term:
• Can weaken organism and lead to onset of malignant tumors, even after
fairly long time delays.
• Largest source: X–rays
• Sr-90 isotopes are present in fallout from atmospheric testing of nuclear
weapons.
• Contaminated foods can increase incidence of leukemia and bone cancers.
65
25.4
Using Radiation
How are radioisotopes used in medicine?
• Neutron activation analysis is a procedure used to
detect trace amounts of elements in samples.
• Neutron activation analysis is used by museums to detect
art forgeries, and by crime laboratories to analyze
gunpowder residues.
• Radioisotopes can be used to diagnose medical problems
and, in some cases, to treat diseases.
25.4
Using Radiation
This scanned image of a thyroid gland shows where
radioactive iodine-131 has been absorbed
25.4 Section Quiz.
1. Ionizing radiation can remove _______ from
atoms.
a) protons
b) neutrons
c) positrons
d) electrons.
25.4 Section Quiz.
2. Which of the following is NOT a device used
to detect radiation?
a) geiger counter
b) scintillation counter
c) film badge
d) radioisotope
25.4 Section Quiz.
3. Choose the correct words for the space. When
a tumor is treated by radiation, more cancer
cells than normal cells are killed because cancer
cells ____________ than normal cells.
a) are more susceptible to damage because they grow
faster
b) absorb more radiation because they are larger
c) grow slower
d) are smaller
25.4 Section Quiz.
4. How do scientists detect thyroid problems?
a) with teletherapy
b) by neutron activation analysis
c) using an iodine-131 tracer
d) using a radioisotope sealed in a gold tube
Practice problems
1. Using the examples above, write the reaction of
bismuth-214 emitting an alpha particle
214
83
Bi Tl  He
210
81
4
2
2. Write the reaction of silicon-27 emitting a
beta particle
27
14
Si P e
27
15
0
1
72
for Sample Problem 25.1
Time
amount
0 hours
1.0 mg
2.6 hours
0.5 mg
5.2 hours
0.25 mg
7.8 hours
0.125 mg
10.4 hours
0.0625 mg (6.25x10-5 g)
73
Study Guide:
• 25.1
Becquerel, Curie
radioactivity, radioisotopes
alpha, beta, gamma particles/decay
• 25.2
neutron-to-proton ratio determines the type of decay
that occurs
half-life
transmutation, transuranium elements
• 25.3
fission, nuclear reactor
fusion, sun/hydrogen bomb
• 25.4 health uses/detection
• Presentation information!; homework problems; lab 74
Research Presentations—what do you want to know?
• What is chemotherapy? What is radiation therapy?
• What other types of things involve fission and fusion?
• What type of radiation is good? Bad? (such as food
irradiation, MRI’s, dyes,…)
• How is solar radiation nuclear?
• Is solar power an answer to our limited supply of
coal? Why or why not?
75