Unit 4:
Applications of Nuclear Chemistry
Including Changes in the Nucleus
Changes in the Nucleus
• Nuclear Reaction- rxn that affects the nucleus
of an atom.
– Changes the composition of an atom’s nucleus
• 3 kind of radiation:
1.
2.
3.
Alpha particles 2+ charge
Beta particles 1- charge
Gamma rays have no charge
• Radioactivity- the spontaneous emission of
radiation from an atom’s nucleus.
Nuclear Stability
• If: protons have a positive charge, nucleus
is made of protons and neutrons, like
charges repel; how does a nucleus stay
together?
• Strong Nuclear Force- an
attractive force STRONGER than
the electric repulsion force btwn
protons. Only exists btwn
particles (protons) extremely
close together.
– The presence of neutrons adds a
net attractive force in the nucleus
Types of Radioactive Decay
α
4
He
2
• Alpha radiation- has 2
protons and 2 neutrons
(same as a helium-4
nucleus).
– Do not have much penetrating
power, can be stopped by
paper or skin. Does not pose
a health problem.
β
• Beta particle- mass=0 but has a charge -1.
Essentially an electron.
– Can penetrate paper and skin. Does present a
health hazard.
γ
• Gamma rays- extremely high energy ray or
light.
– High penetrating power. Very dangerous and
hazardous to your health.
Radioactive Decay
• Radioactive Decay- when an atom emits any type
of radiation.
– Results in a new nucleus. The original nucleus decays
(breaks apart) to form a new, smaller/lighter nucleus.
Nuclear Equation- rxn that affects the
nucleus of an atom.
“In any radioactive decay, the sum of the mass #s
and the atomic #s are the same before and after
the reaction.” (on both sides of the arrow)
Try solving:
Applications of
Nuclear Chemistry
Radioisotopes
• Radioisotopes- an
isotope of an element
which is unstable
(radioactive).
Half-Life
• All radioactive isotopes decay at different rates.
• Half-Life- t½ , is the time required for half the atoms
of a radioactive nuclide to decay.
– More stable nuclides decay slowly. Less stable nuclides
have shorter half-lives and decay much more quickly.
Half-life practice problems
• Solve:
– Nitrogen-13 has a half-life of 10 minutes. IF there are 2.00g
of nitrogen-13 at the start, how many grams will exist after
3 half-lives?
– How long will it take 3.8 x 1024 atoms of 10047Ag to
disintegrate to 2.93 x 1023 atoms if the half life of 10047Ag is
24.6 seconds?
– Radioactive copper, 6429Cu, is found in quantities exceeding
pollution standards in the sediments of a reservoir in a
routine check on Monday. The standard allows up to 14
ppm/cubic meter of sediment. On Monday, 59ppm/cubic
meter were measured. The half life of 6429Cu is 12.7
hours. When will the pollution level return to 14ppm?
Nuclear Bombardment Reactions
• We can make stable nuclei by:
– Nuclear Bombardment Rxns- an atom is
bombarded with a stream of particles like alpha
particles.
– When the nucleus is hit, the particles and the
nucleus combine to form a new, unstable, nucleus.
Atom Smashing!
Fermi National Accelerator Laboratory, Illinois
cyclotron
Stanford Linear Accelerator Center, California.
• Can also bombard
with neutrons…
– 1934, Enrico Fermi
figured out that we
can make radioactive
isotopes by smashing
nuclei with neutrons.
Biological Effects of Radiation
• Units of Radiation:
– SI unit: becquerel (Bq)
– more common: the curie (Ci)- only measures
amount of radiation
– Most often used: the rem (roentgen equivalent for man) –
measures amount of radiation & the sensitivity of
the body
• < 150 rem: not fatal but can cause serious damage
• 150 – 1000 rem: Damaging and can be fatal
• > 1000 rem: FATAL!
Measuring Doses & Detecting
Radiation
Dose Amount
• Dosimeter: small badge or
pen warn on the person.
• Like a mini Geiger counter.
• Used to monitor personal
radiation exposure.
• The film is developed after
use, the darker the film the
more exposure experienced.
Radiation Amount
• Geiger Counter: most
common instrument used
for detecting radiation.
– As radiation passes through
it’s window, it ionizes gas in
the cylinder. Ions strike a
charged cylinder and wire
which created an electric
pulse…. Which clicks and is
read on the counter.
Beneficial Uses of Radioisotopes
1. Radiotracers: used to follow a specific
substance as it moves through a natural
system. Ex- your body.
2. Cancer treatment: Fast growing cancer cells
are more susceptible to radiation than
healthy cells. The hope is, cancer cells will be
damaged and die while healthy cells survive
treatment.
3. Food Preservation: can prevent spoiling of
food.
Harnessing the Nucleus:
Fission vs. Fusion
• Besides nuclear decay and bombardment,
there are 2 other types of nuclear reactions.
1. Nuclear Fission
&
2. Nuclear Fusion
Nuclear Fission
• Enrico Fermi bombarded uranium-238
with neutron (s) which eventually
becomes Neptunium- 239 (a heavier element).
• 1938 Otto Hahn & Fritz Strassman
– Tried to replicate Fermi’s experiment but
they also got Barium (a lighter element).
– Couldn’t figure out why. Wrote letter to
Meitner.
• Lise Meitner
– Thought that the nucleus must become
unstable and BREAK APART to form the
lighter atom.
Nuclear fission cont.
• Meitner was RIGHT! but Hahn got the
Nobel prize.
• Nuclear Fission- a large nucleus
is split into 2 smaller nuclei of
approximately equal mass.
Energy & “Missing” Mass
• There is so much nuclear energy in a very
small amount of mass.
– 4.5g of U-235 = 1 persons energy use for 1 year.
– Compared to 15 tons of coal.
• Where does the energy come from?- the
“missing” mass is matter that has been
converted into energy via Einstein’s E=MC2.
Chain RXNs and The Atomic Bomb
• Because, in a fission rxn, neutrons are released as the U
atom breaks apart, they can go and bombard other U
atoms and cause them to break apart.
• Chain Reaction- a continuous series of fission rxns.
The atomic bomb relies on a runaway chain rxn.
http://www.youtube.com/watch?v=qT4mSoZsbzM
http://www.youtube.com/watch?v=RqyBzXYZPoM
Nuclear Reactors
• Nuclear power plants
use the fission process
to heat water into
steam, that drives a
generator. Turning
nuclear reactions into
electricity.
Three Mile Island, Pa
• Lost water, due to
operator error, and the
rising heat could cause
a “meltdown”.
• Water was restored and
a disaster was averted.
Chernobyl, Russia
• Used Graphite to absorb
neutrons, graphite ignited
and burned out of control.
Burned for days, destroying
the reactor and releasing
huge amounts of radiation.
• Winds carried the radiation
into Europe… many people
developed cancers,
malformed children, etc.
Nuclear Waste Disposal
• Radioactive fission products build-up
on fuel rods. Eventually the fuel
rods have to be replaced.
• Currently, waste stored at site. Best
solution burial but no country has an
underground site.
• Yucca Mountain- was designed to be
the U.S.’s underground storage site.
Nuclear Fusion
• Nuclear Fusion- 2 small
nuclei join to form a large
nucleus.
– Releases a considerable
amount of energy.
• Down side- difficult to produce
and hard to control!
Type of nuclear rxn that takes place
on the sun.
The Hydrogen Bomb!
• http://www.youtube.com/watch?v=NNcQX03
3V_M
• Releases much more energy than an atomic
bomb.
• Triggered by a small atomic blast.
• Only tested, never used in a conflict.
Fusion Research
• Gram for Gram, fusion rxns releases more
energy than fission rxns.
• Controlled fusions are difficult and require
temps of 40 million K or more. (difficult!- no
material can withstand that kind of temps.)
Cold Fusion??
• 1989- Pons & Fleishman @ the
University of Utah.
• Claimed to achieve cold fusion
by the electrolysis of heavy
water (D2O).
• Didn’t work out as claimed.