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Nuclear Notes:
Structure
and
Radioactivity
Online @ redwood.org/stewart
I. Structure of the Atom
Recognize
Me?
Draw
Me!
II. Periodic Table
Atomic # vs. Atomic Mass
A. Atomic No. - number of protons in the nucleus
B. Atomic mass - the sum of the mass of protons, neutrons, and
electrons.
1. no. of neutrons = atomic mass - atomic no.
2. no. of neutrons is not always the same!
isotopes - atoms of the same element (same number of protons)
that have different number of neutrons
III. Radioactivity
a.k.a. radiation
The emission of particles due to the breakdown of atomic nuclei
A. The activity of unstable isotopes (radioisotopes). Isotopes
and large atoms are unstable and will break apart.
B. Nucleus is decomposing, defined as losing
mass/particles, and/or energy
C. Decomposition continues until enough mass has been
lost making the atom stable again. New, lighter atoms are
formed, releasing radiation in the process.
Therefore
Unstable = radioactive
IV. Types of Radiation
These 3 types of radiation are all naturally-occurring.
A. Alpha () particle (Helium atom):
1. charge of +2
2. mass of 4
3. The atomic # of the
decaying atom decreases
by 2 and the mass
decreases by 4
4. Effective shielding materials
include paper and dead skin


Symbol


Sum of mass
numbers (p + n)
and sum of atomic
numbers (p)
is the SAME on
both sides of
equation.
B. Beta (  ) particle (electron):
1. negatively charged: charge of -1 [otherwise known as an electron (e-)]
2. no measurable mass
3. this type of decay/radiation occurs when one neutron is converted to a
proton, thus increasing the atomic number by 1.
4. The atomic # of the decaying atom increases by 1and the mass does not
change. Effective shielding materials include plastic, glass and aluminum
Symbol


Sum of mass
numbers (p + n) and
sum of atomic
numbers (p)
is the SAME on both
sides of equation.




C.
Gamma ( ) radiation:
1. high energy photon
2. powerful and dangerous
can penetrate 3-4 cm of lead
4. virtually all nuclear reactions have this (including naturally and nonnaturally occurring reactions)
5. no measurable mass, no charge no change in mass
6The atomic number and mass of the decaying atom do not change. Effective
shielding materials include thick lead and concrete
Symbol



Sum of mass numbers
(p + n) and sum of
atomic numbers (p)
is the SAME on both
sides of equation.
Where does the
gamma radiation
come from? Mass is
converted into
energy (more on
this later).
Radiation Summary Slide
V. Nuclear Fission
A. The nuclear reaction the world currently uses to generate any
and all usable nuclear energy--not naturally occurring.
B. Fission: the splitting of a large atom into smaller fragments
(particles and/or smaller atoms)
C. A large atom is struck by a single neutron. Smaller atoms are
created. Energy and neutrons are released
D. The most common large atom used:
Uranium (U) - 235 *** atomic number 92
Sum of mass
numbers (p +
Ques? How many neutrons does U-235 have?
n) and sum of
atomic
Answer: 235 - 92 = 143
numbers (p)
is the SAME
on both sides
of equation.

QuickTime™ and a
H.263 decompressor
are needed to see this picture.
VI. Nuclear Fusion
A. Fusion: the combining of 2 smaller atoms into a
larger atom--not naturally occurring on earth.
B. Only possible with isotopes of Hydrogen.
Trit

He
Neutron
Nuclear Energy Summary Diagram
VII. Where does the kinetic energy
in a nuclear reaction come from?
• The mass of protons
and neutrons varies
depending on what
atom they are in.
The mass of protons
and neutrons before a
nuclear reaction is
GREATER than after
the reaction.
Fusion
Fission
VII. Where does the kinetic energy
in a nuclear reaction come from?
• The mass is TRANSFORMED into kinetic
energy according to Einstein’s famous
equation:
• E = mc2 -- mass IS energy!
• Energy equals mass times the speed of light
squared. The speed of light is 300,000
kilometers per second, so even a very small
mass produces a LOT of energy
!
VIII. Energy Evolved
A. FISSION: 1 gram of U-235 evolves 2x107 Cal/g
(20 million Cal/g)*
* which equals the heat from 30 tons of TNT
1 gram of Uranium = 20,000,000 Cal
Versus
1 gram of oil = 9.8 Cal
B. The energy released in nuclear FUSION is about 7
times greater than the energy released in the fission of
Uranium. 10 grams of Deuterium which can be extracted from 500
liters of water could produce enough fuel for the lifetime electricity
needs of an average person in an industrialized country.
VII. Advantages and Disadvantages of Using Nuclear Fuel
A.
B.
Advantages:
•
Fuels are plentiful.
•
If shielded properly, it is inherently safe since any
malfunction results in a rapid shutdown.
•
No atmospheric pollution leading to acid rain or global
warming.
•
Small amounts of mass yield high amounts of energy.
Disadvantages:
•
What are some disadvantages of using Nuclear Fuel to
generate electricity?