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Nuclear Chemistry
Antoine Henri Becquerel
(1852-1908)
• February 1896. Antoine Henri Becquerel, a French scientist,
was conducting an experiment which started with the exposure
of a uranium-bearing crystal to sunlight. Once the crystal had
sat in the sunshine for a while, he placed it on a photographic
plate. As he had anticipated, the crystal produced its image on
the plate. Becquerel theorized that the absorbed energy of the
sun was being released by the uranium in the form of x-rays.
• Further testing of this theory had to be put off for a few days
because the sky had clouded up and the sun had disappeared.
For the next couple of days he left his sample of uranium in a
closed drawer along with the photographic plate.
• When the weather had cleared, he returned to the drawer to
retrieve his gear. He was surprised to find that the crystal had left
a clear, strong image on the photographic plate.
• How could this be? There was no source of energy to produce
the image! What Becquerel had discovered was that a piece of
mineral which contained uranium could produce it's image on a
photographic plate in the absence of light. What he had
discovered was radioactivity! He attributed this phenomenon to
spontaneous emission by the uranium.
Pierre Curie (1859-1906)
Marie Curie (1867-1934)
• The husband and wife team of Pierre and Marie Curie became
interested in Becquereal's discovery. While experimenting with
their own uranium-containing ore, they came up with the term
"radioactivity" to describe the spontaneous emissions that they
studied. This word is still used today to describe this special
characteristic of some elements.(radioisotopes).
• While comparing the activity of pure uranium to a uranium ore
sample, they found that the ore was significantly more
radioactive than the pure material. They concluded that the ore
contained additional radioactive components besides the
uranium. This observation led to the discovery of two new
radioactive elements which they named polonium and radium.
Did you know this??
• In 1903, Becquerel and the Curies together received the Nobel
Prize in physics. This award was for their discovery of
radioactivity and their other contributions in this area.
• Marie Curie received a second Nobel Prize in 1911 for the
discovery of polonium and radium. She was the first person to
win two Nobel Prizes.
• Did you know that the Curie's had a word named after them?
The curie is a basic unit of measurement for describing
radioactivity.
Types of Radiation
• Alpha particles:
α
• Positively charged …essentially the nucleus of a helium atom
• 2 neutrons and 2 protons
• They travel short distances, have large mass
• Beta particles:
β-
• Negatively charged….electrons emitted when a neutron decays to
form a proton and emits the beta particle
• Gamma radiation:
γ
• High energy radiation…more energy than x-rays!
• Released by nucleus along with beta and alpha decay
Penetrating Power
• Alpha radiation can be stopped by a sheet of paper; beta can
be stopped by a sheet of plastic; gamma is stopped by several
inches of lead or several feet of concrete!
Natural Transmutation
 Transmutation = change of nucleus of an atom of an element
to another element (must involve a change in the number of
protons!)
Natural transmutation = the change of naturally radioactive
elements by emission of a radioactive particle
 Isotopes of elements with atomic numbers less than 20
whose neutron: proton ratio is NOT 1:1 are likely to
undergo spontaneous nuclear “decay” (i.e. loss of a
radioactive particle) (for example…. carbon-12 is stable,
carbon-14 is radioactive)
All isotopes of elements with atomic numbers > 82 are
radioactive (“unstable”)
Beta Decay
• Converts a neutron to a proton and an
electron
19 protons
23 neutrons
20 protons
22neutrons
Positron Decay
• Converts a proton to a neutron and a
positron (anti-matter of electrons)
Balancing Nuclear Equations
• In order to balance nuclear transmutation
reactions, the number of protons and total mass
must remain the same on both sides of a nuclear
equation.
Artificial Transmutation
• Artificial transmutation = isotopes that are NOT naturally
radioactive can be transmutated by “bombardment” with
nuclear particles.
Half-Life
• amount of time required for one-half of the
isotope to undergo radioactive decay
• The half-life of a radioisotope CANNOT be
changed!!
• # of half-lives amount remaining
0
1
1
1/2
2
1/4
3
1/8
Half-Lives can vary….
How many days must elapse for I-131 to undergo 3 half-lives?
How many half-lives will Sr-90 undergo in 112 years?
Nuclear Energy
• All nuclear energy is derived from the conversion
of small amounts of mass to energy.
• Einstein’s relativity equation E = mc2 explains the relationship
between matter and energy
(c = 3.00 x 108 m/s …it is the speed of light)
• When the mass of nuclear reactants (before) is compared to
the products (after), a small amount of mass is
unaccounted…this is called the mass defect and is the mass
that is converted to energy
Nuclear Fission
• All existing nuclear
power plants use
nuclear fission as the
source of energy
• Fission involves the
splitting apart of large
nuclei into smaller nuclei
with the release of large
amounts of energy
• A commonly used
reaction involves the
capture of a neutron by
a U-235 nucleus and its
splitting apart into Ba141 and Kr-92 plus 3
neutrons
Fission
Pros
Cons
• Releases more energy
than conventional fuels
• No greenhouse gases
• Viable source of energy
(we can do it!)
• U-235 accounts for only
3% of the world’s
uranium
• Non-renewable resource
• Highly radioactive waste
products (difficult to
dispose)
Nuclear Fusion
• Fusion involves the joining
of small nuclei to release
large amounts of energy
• One of the most common
reactions involves the
joining of H-2 (deuterium)
and H-3 (tritium)atoms to
form He-4 and a neutron
• Fusion powers our sun!!
Fusion
pros
• Much more energy than
fission
• Abundant fuel (H-2 and
H-3) in sea water
• Safe, non-toxic, stable
waste products
cons
• Requires extremely high
pressures and
temperatures to
overcome repulsion by
nuclei
Nuclear Accidents
• March 1979
• Three Mile Island, Pa
• Partial meltdown
released radiation
• No immediate deaths
• April 1986
• Chernobyl, Ukraine
• Worst nuclear
disaster in history,
released more
radiation, 31 deaths
Risks of Exposure to Radiation
How does radiation cause
health effects?
• alpha, beta and gamma radiation are forms of ionizing radiation,
which has enough energy to strip away electrons from atoms
(creating ions) or to break some chemical bonds
• living tissue in the human body can be damaged by ionizing
radiation …the body attempts to repair the damage, but
sometimes the damage cannot be repaired or it is too severe or
widespread
• mistakes made in the natural repair process can lead to cancerous
cells
• because children are growing more rapidly (and their cells are
dividing more rapidly), they are more sensitive to radiation effects
• radiation can also cause damage to DNA, leading to mutation in
offspring
How much radiation is needed
to cause health effects?
Exposure
(rem)
Health Effect
5-10
changes in blood
chemistry
50
nausea
55
fatigue
70
vomiting
75
hair loss
90
diarrhea
100
hemorrhage
400
possible death
1,000
destruction of intestinal
lining
Time to Onset
(without treatment)
hours
2-3 weeks
within 2 months
internal bleeding
and death
2,000
1-2 weeks
damage to central
nervous system
loss of consciousness;
minutes
and death
hours to days
Some radioactive elements are
more dangerous than others
• organs in the body use an element cannot distinguish
between radioactive and non-radioactive isotopes
• radioactive iodine concentrates in the thyroid, because the
thyroid needs iodine to function normally
• calcium, strontium-90 and radium-226 have similar chemical
properties. …so strontium and radium in the body tend to
collect in calcium-rich areas, such as bones and teeth. They
contribute to bone cancer
• radioisotopes with long half-lives emit radiation slowly, while
those with short half-lives emit radiation more quickly
Calculate your exposure…
• http://www.ans.org/pi/resources/dosechart/
Benefits of Radioisotopes
Medical Uses:
• Iodine-131
• because the thyroid uses iodine,
radioactive iodine can be used to detect
and treat thyroid disorders
• Tc-99
• most commonly used radioactive tracer
• used to track blood flow in heart and brain
• (tumor detection)
• Co-60
• used as a source of gamma
radiation targeted to cancer
cells.
• proper dosage can destroy
cancer cells and preserve
healthy cells
Benefits of Radioisotopes
• Tracers
• used to follow pathways of chemical reactions
• Phosphorus-32
• traces fertilizer uptake in plants
• Carbon-14
• traces carbon in organic reactions
• Hydrogen-3 (tritium)
• traces hydrogen in chemical reactions
Benefits of Radioisotopes
• Dating
• determines the age of objects
• Carbon-14:
• percent of carbon 14 present in
all living things is constant
• when an organism dies, carbon14 is no longer replenished
• using ratio of carbon-14 to
carbon 12, the age of a fossil can
be determined
• Uranium -238
• used to determine the age of
rocks (“geologic formations”)
Miscellaneous Benefits
• Americium-241
• used in smoke detectors!
• ionizes air, smoke disrupts the ionization, causing alarm to sound
• Radiation is used to kill bacteria in fresh fruits, vegetables and
meats!