Ch. 25- Nuclear Chemistry (originally ch. 18 from old textbook)

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Ch. 25- Nuclear Chemistry (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

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
Hulks powers began when nuclear scientist Dr.
Bruce Banner was accidentally bombarded with
gamma rays from a "gamma bomb" he had invented.
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Chemical reaction vs. Nuclear reaction
Nuclear chemistry the chemistry of radioactive
substances study of the atomic nucleus,
including fission and fusion and their products

• Chemical reactions
• Atoms attain stable isotopes by losing or
  sharing electrons
• Reactions affected by changes in temperature,
  pressure, or the presence of catalysts

Nuclear reactions The nuclei of unstable
isotopes gain stability by undergoing
changes The changes are accompanied by emission
of large amounts of energy
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Atomic Review

• Atomic number
• Every atom of an element has the same atomic
  number because the p defines the element.

of p

• Mass number (or atomic mass)
• The n may vary without changing the element.

sum of p n
X

• Atomic notation

Mass
Atomic
Ex magnesium atom with 13 n
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Practice

• Fill in the blanks

Name Symbol p n
Hydrogen-1
Helium-5
Carbon-13
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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 gt electrostatic gt weak gt 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.

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Natural Radioactivity

• Discovered in 1895 by Antoine Henri Becquerel,
  who observed that a uranium salt produced an
  image on photographic filmthought the film had
  to be exposed to sunlight, but the plates fogged
  in a drawer.
• 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.

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Radioactivity
25.1

• 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.

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Types of Radiation
25.1

• The three main types of nuclear radiation are
  alpha radiation, beta radiation, and gamma
  radiation.

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Types of Radioactive Decay
Type Consists of Stopped by Interesting Fact



alpha a He nucleus 2 p 2 n Paper or skin If ingested, is harmful to lungs
beta b High energy e- Clothing, glasses, or thin sheet of Al Causes damage to sensitive tissues like eyes
gamma g Photon (particle of light) Has essentially no mass (m lt 5.81 x 10-72 gits complicated!) A few feet of dirt or concrete, or 6 of Pb Causes severe damage to body tissues
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Alpha decay
Example
236
U
92
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Alpha decay
Example
236
U
92
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Beta decay

• Ex

137
Ba
56
1
p
1
(One of Css neutrons converts to a proton and
electron.)
Beta decay animation http//ie.lbl.gov/education/
glossary/AnimatedDecays/Beta-Decay.html
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(No Transcript)
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Gamma ray emission

• Ex Pu (energized) ? Pu (stable)

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Types of Radiation
25.1

• Gamma Radiation
• A high-energy photon emitted by a radioisotope
  is called a gamma ray. The high-energy photons
  are electromagnetic radiation.

Radium
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Types of Radiation
25.1
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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.

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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.

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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

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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.

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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.

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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.

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Nuclear Stability and Decay
25.2

• 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.
• Positron emission is a byproduct of a type of
  radioactive decay known as beta plus decay. In
  the process of beta plus decay, an unstable
  balance of neutrons and protons in the nucleus of
  an atom triggers the conversion of an excess
  proton into a neutron.

Wisegeek.com
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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.

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Transmutation Reactions

• The first artificial transmutation reaction
  involved bombarding nitrogen gas with alpha
  particles.

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Transmutation Reactions

• 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.
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Disintegration Series

• Heavy atoms (greater than Bismuth, 83)
  naturally decay to smaller atoms along a
  consistent path, or series, of decays.

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/urani
um.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 C-14 which
  happens in the upper atmosphere.
• Plants consume CO2 during photosynthesis and
  animals eat the plants, so they contain the same
  C-14C-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-14C-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/visualgeolog
y/geology101/lab6time.htm http//www.dc.peachnet.
edu/pgore/geology/geo102/radio.htm http//supers
tringtheory.com/cosmo/cosmo1.html
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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.

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Half Life

• Ex
• Phosphorus-32 radioactively decays to form
  Sulfur-32
• Half life 32P 14 days

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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.
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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.

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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.

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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

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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

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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.

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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.

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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.

• 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/n
uclear-bomb3.htm
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• 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 Emc2

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Nuclear Fission
25.3

• 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.

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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
plutonium-239) captures them to continue the
chain reaction.
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Harnessing Fission A nuclear power plant

• Check out http//science.howstuffworks.com/nuclea
  r-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.

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Nuclear Waste
25.3

• 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.

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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 .

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Nuclear Reactor Operation

• Hazards
• Radioactive waste from normal operations.
• Reactor coolant has tritium 1H3 which is
  radioactive with a half-life of 12.3 years.
• Used fuel cells are radioactive and have
  half-lifes in the millions of years.
• 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

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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 10,000,000C.
• Produces shock waves and a, b, g, x-rays, and UV
  radiation.

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A Fission Chain Reaction
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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.
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Detecting Radiation
25.4
A film badge consists of several layers of
photographic film covered with black lightproof
paper, all encased in a plastic or metal holder.

• A Geiger counter uses a gas-filled metal tube to
  detect radiation.

A scintillation counter uses a phosphor-coated
surface to detect radiation.
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Biological Effects of Radiation

• Acute
• High level radiation (gamma ray xray) 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 Xrays
• Sr-90 isotopes are present in fallout from
  atmospheric testing of nuclear weapons.
• Contaminated foods can increase incidence of
  leukemia and bone cancers.

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Using Radiation
25.4

• 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.

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Using Radiation
25.4

• This scanned image of a thyroid gland shows
  where radioactive iodine-131 has been absorbed

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25.4 Section Quiz.

• 1. Ionizing radiation can remove _______ from
  atoms.
• a) protons
• b) neutrons
• c) positrons
• d) electrons.

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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

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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

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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

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Practice problems
1. Using the examples above, write the reaction
of bismuth-214 emitting an alpha particle
2. Write the reaction of silicon-27 emitting a
beta particle
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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)
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Study Guide

• 25.1Becquerel, Curieradioactivity,
  radioisotopesalpha, beta, gamma particles/decay
• 25.2neutron-to-proton ratio determines the type
  of decay that occurshalf-lifetransmutation,
  transuranium elements
• 25.3fission, nuclear reactorfusion,
  sun/hydrogen bomb
• 25.4 health uses/detection
• Presentation information! homework problems lab

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Research Presentationswhat 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, MRIs, dyes,)
• How is solar radiation nuclear?
• Is solar power an answer to our limited supply of
  coal? Why or why not?