Chapter 17
Radioactivity and Nuclear Changes
Why do I have to know this stuff?
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We could all be vaporized.
Or…nuclear energy could be our salvation.
How old is that fossil?
Can we treat that tumor?
Radon (a bigger problem elsewhere)
Food preservation (refrigerated, is it safe after 3
days or 3 weeks?)
Is grandma losing her mind?
Positron emission tomography
Age: 20 -- 80 Normal -- 80 with Alzheimer’s
Postmortem Coronal Sections
Normal
Alzheimer’s
PET images courtesy of the Alzheimer's Disease Education and Referral Center/National Institute on Aging; Postmortem images
courtesy of Edward C. Klatt, Florida State University College of Medicine
There are important differences between chemical and
nuclear reactions; let’s begin with this chemical reaction.
CCl4 + H  CCl3H + Cl
Chemical Reaction—let’s do it by Lewis Dots
Note: no atoms lost, just rearranged.
Now here’s a nuclear reaction.
CCl4  NCl4+ + 1 eCarbon turned to Nitrogen. Can it do that?
Nuclear Reactions
New elements often
formed
Particles in the nucleus are
involved
Chemical Reactions
Elements stay the same
Only electrons are involved
Huge energy available
Normal amounts of energy
Not affected by
temperature, pressure, etc.
Affected by surroundings
The number of nucleons
remains the same
The number of atoms remains
the same
Sum of atomic numbers
(positive charge) remains
the same.
Number of electrons remains
the same
Becquerel’s Experiment
Antoine Henri Becquerel
Comptes Rendus 122, 420 (1896)
Nobel: 1903 with P. & M. Curie
*Mr. B was studying phosphorescent light.
*Was it the same as ordinary light?
*Would it expose photographic film in the same way?
*Today, we know it will…but Mr. B’s source was rocks.
*He placed certain “ordinary” non-phosphorescent
Image: Wikipedia
rocks….and they exposed the film, too! This
was true even if the film was shielded from normal light.
Serendipity means lucky.
The greatest results often come just when we aren't
looking for them. In fact, looking for some specific
result can blind you to more important things.
Most scientists struggle with this problem, especially
today because science has become a means to an end.
Nuclear Reactions Convert Small
Amounts of Mass to Energy
E=
2
mc
Chocolate bar: 35 g = 0.035 kg
Nuclear Energy: (0.035 kg)(3 x 108 m/s)2 = 3 x 1015 Joule
Chemical Energy: 200 food cal = 200,000 cal = 800,000 Joule
Nuclear energy 4 billion times greater! But
it is not so easy to convert chocolate to energy
especially if you want to do it quickly.
Why atomic weapons are so powerful
It is possible to convert a fairly small portion of some isotopes
of some elements (uranium, plutonium, hydrogen) into energy.
Even though the portion of matter converted is small,
the “bang” is pretty large because….
the conversion process is very quick. Energy changes
that happen quickly imply high power.
A populace that is burning millions of candy bars can
equal the energy of a nuclear bomb, but not the power.
Also, the A-bomb is small, concentrated energy, whereas
all the people to burn those candy bars would be spread out.
Atomic weapons & results—friend or foe?
“Runt 1”, a very large
nuclear weapon
It is possible for such weapons
to produce craters 250 feet deep,
more than one mile wide.
Castle Romeo Test Shot
Is it possible for them never to be used again?
From the Gallery of U.S. Nuclear Tests
http://www.fas.org/nuke/hew/Usa/Tests/index.html
Meet the Nucleons.
(kind of a repeat)
Name
Alpha, 
Penetrates
several cm air
Symbol
Beta, 
paper
Gamma, 
1/4” lead
0
1 e
0
0
neutron
armor
positron
like electron
What is it?
helium
nucleus, +2
charge
electron
4
2 He
1
0n
0
1 p
very energetic
photon
neutron(**)
or
0
1 e
one form of
antimatter
The symbols are designed to help us track
nuclear reactions.
mass / amu
ch arg e ConvenientSymbol
All symbols have this meaning.
Upper left: mass in multiples of hydrogen mass
Lower left: charge
Main symbol: an atomic symbol or n for neutron, etc.
There are only 100 or so elements, but many
have multiple isotopes, some are radioactive.
“stable”and “unstable”
may be inverted
on this figure. Someone
want to look that up?
Figure 5.3 (stable & unstable isotopes)
All those isotopes are why the mass numbers for an
atom are not simple integers.
average mass of carbon = 12.01
the 12 isotope is very common, and
only small portions of the fatter
isotopes are found.
the 13 isotope is useful for identifying
compounds in nuclear magnetic
resonance.
the 14 isotope is useful for
radioactive dating of ancient
objects.
Rules for nuclear reactions
The total mass does not change*
The total charge does not change
*Except for the tiny amount converted to pure
energy, as discussed already.
Work some of the examples in the
notes—write them on ELMO
Types of nuclear processes are referred to by
the ray or particle they produce.
Nuclei can eject protons or helium nuclei & get lighter (alpha decay).
They can swallow a neutron & spit out the electron to get heavier (beta decay).
Whenever the # of protons changes, the atom type has changed.
Figure 5.6 Uranium Decay Path
Where does a 900-pound gorilla sit?
When does radioactive decay occur?
Decay events—e.g. electrons detected
for beta decay—most probable at first
As radioactive molecules become
depleted, detected events decrease.
Half-life
Half-life Problems
Practical nuclear reactions
Fusion example (sunlight, future perfect energy source?)
4 H
 He  2 e  2 γ  2 ν
1
1
4
2
0
1
0
0
0
0
4 hydrogens  1 alpha + 2 positrons + 2 gammas + 2 neutrinos + ENERGY
Fission example (atomic bombs, power plants)
235U
+ 1n 
134Xe
+ 100Sr + 2 1n + energy
http://www.lbl.gov/abc/Basic.html
LSU Peptide-based Alzheimer Inhibitors
K
L
V
F
F
MCP 1
AMY-1 x = 1, y = 6
AMY-2 x = 6, y = 1
AMY-3 x = 1, y = 1
K
L
V
F
F
MCP 2
Mediators Developed by Professor Robert Hammer & Professor Mark McLaughlin
Stop here?